By Bob Goemans
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The 'LIVING' Marine Aquarium Manual

Basic and Advanced Husbandry for the 'Modern' Marine Aquarium

by Bob Goemans

Chapter 5 - Lighting Equipment

Light, from that big shiny globe in the daytime sky, nourishes much of what we see in our everyday life.

When it comes to our aquariums, the topic of light itself and the equipment utilized to generate and control it is one of the more debatable subjects that surround the hobby! And since light is important for the proper maintenance of much of the flora and fauna we hobbyists prefer to sustain, beginning such an endeavor with the correct quality and quantity of light to accomplish one's goal is extremely important. Keep in mind; it's far more cost-effective to do it right the first time than replace an inadequate light unit! And where reef aquaria are concerned, poor quality and/or incorrect light quantity can possibility lead to losing some photosynthetic animals.

To accomplish the goal of this chapter, it's my opinion the logical way to begin is with an understanding of light itself, then work our way into how light is 'engineered' for our uses and then proceed to the equipment that's the most widely available and used in today's hobby. Then finally, in this chapters 'summation,' look at some viewpoints on the general subject matter now that key words have been defined and look at some suggested combinations of equipment for various aquarium goals. Just keep in mind this chapter is considered a 'snapshot' of the multitude of aspects pertaining to lighting equipment and usages, not a defined stance on the usage of particular lighting equipment for certain aquarium systems, as that is up to the reader/user to define.

To begin, when it comes to lighting anything, whether it's the home, place of business, and/or the fish or reef aquarium there are two very important key words — INTENSITY (PAR) and SPECTRUM (Kelvin). Both should be completely understood before investing in lighting equipment. In addition I've added some other terminology and data that may help those new to the hobby to make more informed choices.

Without a doubt this whole subject needs to have some more 'light' shed on it! Forgive the pun, I couldn't resist.

(Please keep in mind all underlined word(s) are linkable files – just click on them and be taken to its content/photo. Also, all shown photos are clickable, which often allows a larger file to be seen.)


Various books noting light needs of some aquatic animals in terms such as 'bright light for so many hours per day' are helpful, but far from adequate. That's because too many variables exist in closed systems to accurately or easily judge the intensity of the light reaching its target, e.g., the quality/clarity of the water the lightwaves need to penetrate or the type or age of its lamps, etc., to give anything but a somewhat educated guess. But for all practical purposes, it's better than pure guesswork! (When reaching Chapter 16 and 17, will actually give the recommended PAR value for many of the photosynthetic animals discussed, along with an explanation of their water movement needs!)

Since humans cannot duplicate natural sunlight or the weather conditions that occur in the wild, I can understand hobbyist concerns as to proper intensity/spectrum and the correct photoperiod. And when it comes to reef aquariums, some of the animals we strive to keep in these type systems are in some ways similar to algae (desired and unwanted), as both need light energy to prosper. As for those invertebrates/corals that require light energy, they contain living alga cells called 'zooxanthellae' inside their tissue. These cells are a vital part of the animals' food chain and need the right amount of light (intensity), color (spectrum), and photoperiod (length of time lit) to manufacturer the nutritional needs that help to keep their hosts alive. If its zooxanthellae die, the host soon follows.

Keep in mind that in fish-only aquariums we usually only want enough quality light to view the fishes; with wide/broad spectrum fluorescent lamps possibly still a good choice. Yet in the reef aquarium where many of its invertebrates were accustomed to sunlight, both spectrum and intensity are critical factors to their long-term success. And knowing what wavelength of the visual spectrum and its intensity level is required to trigger photosynthesis is a good part of the key in maintaining them. This is why it's a must to design a lighting system around these requirements.

Judging Light Intensity

There are basically two measurements frequently available to help judge light intensity, Lumens/Lux, and PAR, with a third, PUR, sometimes available for the more experienced aquarist.


The Sun on a clear day can exceed 100,000 Lumens/Lux on one square meter of ocean surface.

Yet for aquarium purposes this terminology is misleading since it's geared to what the human eye perceives, which is more sensitive to mid range colors in the visible spectrum, e.g., green and yellow. Kelvin and PAR are 'really' the important values!

For what's its worth, most of the corals we strive to maintain come from a depth of about 20 feet, and said areas have a lumen/lux intensity of about 5,000 - 15,000 in excellent clarity of water and at the peak sunny time of the day (about 2pm).

Nonetheless, if of interest, you can measure it with what is called a Luxmeter. These meters are fairly inexpensive and sometimes waterproof, which makes them quite useful if one wants to know how much light is reaching a submerged organism in the aquarium. Simply hold the meter next to the animal and read the value of the transmitted light.

FYI - for providing some 'light' to brighten dark household areas, e.g., kitchen countertop areas, clothes closets, book shelves, where Kelvin and PAR are not important factors, then Lumen ratings can be somewhat helpful.


Photosynthetically Active Radiation (PAR) measures light intensity over the visible spectrum (400 - 700 nm), which is somewhat different from lumens/lux that reports the intensity of those wavelengths to which the human eye is most sensitive (largely the green wavelengths). It can be said that PAR is keyed to photosynthetic response whereas lumens is keyed to human eye response. Therefore, the greater the PAR the more useable light penetration there is into the aquarium, resulting in improved photosynthesis processes. It's measured in units called micro-Einsteins per square meter per second (µE). PAR on a clear sunny day it can exceed 2000 µE on one square meter of ocean surface. For aquarium use, the Apogee MQ-200 Quantum Meter is a good tool for measuring PAR

Yet keep in mind even if a lamp/fixture provides a high PAR level, it may still contain inadequate intensity of the blue and red wavelengths, which are needed by photosynthetic animals for their growth. Therefore, no matter what type lamp(s) your desired fixture may be fitted with, always, and I must repeat, before purchasing it, always view a spectrograph of what that fixture produces in the way of visible light! Remember, most photosynthetic animals do not utilize the full spectral range/visible spectrum that PAR encompasses, but simply respond best to PUR wavelengths (See Below)


The difference between PAR and Photo Usable Radiation (PUR) is the first relates to overall intensity, whereas the second measures the intensity of the wavelengths that simulate photosynthesis, 400 - 550 nm (blue) and 620 - 700 nm (red). Therefore, if a PUR factor, as percentage of the PAR rating is supplied by the lamp manufacturer, it will denote what portions of the available intensity are useable to excite the photosynthesis processes in zooxanthellae and plants. Consider it a usable yardstick as to the lamp's capability to simulate photosynthesis, e.g., 75% of available PAR is in the PUR ranges. Yet exactly what PAR/PUR percentages certain species require, is still open to much speculation.


This key word in the lighting world is defined by Webster's Dictionary as a series of colors formed when a beam of white light is dispersed (as by passing through a prism) so the component waves are arranged in order of their wavelength from red continuing through orange, yellow, green, blue, indigo, and violet.

The Sun, a star located at the center of our solar system emits a broad 'spectrum' of energy waves, some of which we can see and some which the human eye cannot. The light the human eye perceives is known as the 'Visual Spectrum' and is only a small portion of the total electro-magnetic radiation/spectrum (EMR) discharged by the Sun.

When we see a rainbow we are witnessing a breakdown of the colors that comprise the visual portion of the spectrum, e.g., violet, indigo, blue, green, yellow, and red. The violet/indigo/blue portion of this 'visible' light begins at a wavelength of 400 nanometers (nm). (Light wavelengths are measured in 'nanometers, with 1 nm equivalent to one-thousand-millionth of a meter.) They then change to green at about 475 nanometers, then to yellow at about 580 nanometers, which is the brightest portion of the visual spectrum. At 625 nanometers yellow changes to red, which continues to be visible until it reaches about 700 nanometers.

Beyond this range, the spectrum consists of infrared wavelengths and is invisible to the human eye. Below the 400 nanometer range the spectrum is also invisible to our eye and it's this portion of the spectrum that contains the cosmic, gamma, x-rays and ultra-violet wavelengths. The human eye perceives the blue and red wavelengths of the visible spectrum as the darkest areas of this light source; however, they are the wavelengths that trigger photosynthesis!

If we were to engineer a lamp to give off a certain color, e.g., yellow, it would be brighter than any of the other visible colors given the same amount of energy. Therefore it's a lot less expensive to light places such as parking lots, ball fields, and streets with 'yellow' light. Yet, lamps such as these have no value for photosynthetic invertebrates as they lack or have insufficient amounts of the spectrums needed to trigger photosynthesis.

Often, a graph/chart called a Spectral Power Distribution Curve Chart/spectrograph is encountered showing the spectrum generated by a lamp, which depicts a series of peaks and valleys over the visible spectrum range – ultraviolet to red. This is helpful, as it gives one an idea of the amount of light that is generated at each wavelength and what to expect as to the appearance of the light, e.g., lamps with peaks in intensity at the shorter wavelengths will look bluer and those at the longer wavelength will look more reddish. Lamps called 'Full Spectrum' tend to have a spectrum that closely matches that of natural daylight, which has a very broad peak in the middle of the visible spectrum/graph. The manufacturer of these lamps use a very expensive piece of equipment called a spectroradiometer to supply this measurement/graph.

As possibly an interesting side note, the interpretation of what color our eye sees depends somewhat on the color light the object is viewed by, how long we look at it, what color objects it's associated with, and possibly what color object we just saw previously or what we may want to see. Because of that some standards of judging the color rendered by lamps is needed, and there are a few different methods you may find 'enlightening.'

C.I.E. Color Triangle

The International Commission on Illumination's Color Triangle is a three-sided graph that has its perimeters represented by the different colors of the visual spectrum. As the coordinates inside this triangle move towards its central area the colors blend until they become white at the exact center. By specifying the coordinates inside the C.I.E. Color Triangle an engineer can mathematically locate a color or blend of colors that a lamp can be designed to reproduce. Then using known materials that when heated to a certain temperature, radiate those desired colors.

Color Temperature - Chromaticity/Kelvin

When a piece of metal is heated its color changes as it gets hotter. The progression of color, matched to its temperature (measured in Kelvin's), can be plotted on the C.I.E. Color Triangle to further define 'color.' If there is anything about this subject matter that should be remembered its that lamps emitting a color temperature of less than 5500K (Kelvin) are not beneficial for reef aquariums. They are simply too low in the blue wavelength. Actually, 5500K is a noontime temperature and should be considered the absolute minimum color temperature for any lamp used to light a reef aquarium. Higher color temperature lamps, such as 10,000 to 20,000K are better suited to supplying the needs of photosynthetic animals and provide a more visually pleasing environment to the human eye.

Color Rendering Index

The previous two methods of charting a color do not take into consideration how natural or unnatural objects will look to the 'human' eye when illuminated by certain lamps. Therefore this international index, rated from zero to 100 was devised. However, there are so many variables in this system of measurement its only mention here so that should you see a high index number on a lamp, you consider it only a 'general' indicator of the lamps ability to provide a natural looking environment.

In reality there are many lamps that provide a natural appearance 'and' also provide the other qualities reef keeper's need, e.g., spectrum (Kelvin) and intensity (PAR). To find these lamps you need to contact the manufacturer (if not supplied with the lamp) and request a Spectral Power Distribution Curve Chart (depicted above in the topic 'Spectrum' for a 5500 Daylight Fluorescent) as to its peaks and valleys for the various wavelengths over the visible spectrum range that the lamps of interest provide. More about this further along in this chapter.


Wattage is basically how much electrical power a lamp uses. How much light a lamp produces per watt depends upon the lamps technology. Some lamps are more advanced than others and are therefore more efficient at converting electrical energy into light energy. A typical fluorescent tube is about four times brighter than the same wattage incandescent lamp. A metal halide lamp is about twice as bright as an equal wattage fluorescent tube

Wattage may be the simplest way to specify how much light to use, but it is far from an accurate method. Just keep in mind it's a rule of thumb and does not take into account lamp efficiency/efficacy, type of reflector, type of lamp or exactly what is being lit and/or sometimes the depth of the water the light has to penetrate to reach the target organism.

Glitter Lines

For those of us who dive or own a swimming pool, you've no doubt seen those dancing bright ribbons of light on the bottom of a lagoon or pool on a sunny day. Called 'Glitter Lines,' these magnified light rays are caused by refraction of the lightwaves passing through surface waves/ripples. These lines of intense light are thought to act like a magnifying lens and concentrate/focus light and possibly provide pluses of light energy thereby aiding photosynthesis in some invertebrates. In the aquarium, incandescent lamps, e.g., metal halides, with their intense point of light are very good at producing glitter lines. LED lamps are also capable of generating glitter lines. Fluorescent lamps simply spread the light over the length of its tube surface and are usually not intense enough to produce glitter lines.

Ultraviolet (UV) Light

Ultraviolet Radiation (UV) wavelengths begin at about 200 nm and go to 400 nm, and this range is divided into three categories; A: 300 to 400 nm, B: 280 to 320, and C: 200 to 280. The 'C' range is filtered out by the ozone layer that surrounds the Earth. The 'B' range is very dangerous to the zooxanthellae in our photosynthetic animals and can be filtered out by glass. The 'A' range can still be hazardous to many corals, especially those that do not contain zooxanthellae. It is not filtered out by glass, but can be reduced by various types of plastic material. In fact, some of the shallow water coral animals have their own built-in UV filtering cells. With the wide variety of animal possibilities in our aquariums it usually decrees that we limit UV penetration into the aquarium at nothing lower than 350 nm, preferably 385 nm for the general reef aquarium environment, and especially so if constructing a low light aquarium where all animals come from deep water, i.e., a depth greater than about 30 feet (10 m).

As for the clear plastic lens covering the bottom of some lighting fixtures, it may only serve to protect the lamp(s) and you from electrical shock and moisture. Yet, some may filter out some of the more harmful UV wavelengths and also act like as an insulator to keep some of the heat from the lamps from somewhat warming the aquarium water.

There is also no reason to totally filter out all UV light. Some corals, especially shallow water animals, have what is referred to as S-320, a UV protecting compound. This compound is named for the A range 320 nanometer absorbency peak. These and other UV protection compounds give some animals the ability to fluoresce. This can be seen in some invertebrates as a green, white or purple fluorescence. Invertebrates living beyond the range of UV light penetrations tend to have little or no protection against cellular damage. Many of these invertebrates are orange, red, or yellow in color, e.g., red brain coral, gorgonians, Tuberastrea, and Dendronepthya to name but a few. Therefore, these animals should be protected from any UV transmissions.

Moreover, the 380 nanometer wavelength can inhibit calcification in stony coral and shorter wavelengths can damage genetic materials and depress photosynthesis. As noted above, ask for a Spectral Power Distribution Curve Chart pertaining to the lamp of your choice because the well being of your animals may depend upon the data supplied by this reference source. Also, if purchasing a light fixture complete with a plastic lens cover, ask the lighting product company just how much transmittance/admittance the filtering material allows. If it removes all UV below 385 nm, that material is generally considered acceptable.

In fact, Plexiglas 'G' filters out 100% of UV below about 360 nm, and still filters out 50% or more of UV in the 360 - 380 nm range. Apparently, museums are the biggest customers for this material because they use it to construct cases that protect various forms of artwork from UV.

Black Light

Some aquarists have considered using a form of light called 'Black Light,' which is a spectrum in the ultraviolet range. The thought there is that their fish will fluoresce and be more colorful, however, that will not occur.

As previously explained in 'Spectrum' above, when we see a rainbow we are witnessing a breakdown of the colors that comprise the visual portion of the spectrum, e.g., violet, indigo, blue, green, yellow, and red. The combined spectrums of this visible light is what is called 'White' light, as it is a blend of all its individual colors. When white light falls on an object containing different colors, those colors are absorbing their related color spectrums and that is why red looks red, and yellow looks yellow, etc. If the object is white, its simply reflecting back all the colors of the spectrum – hence white is the color seen.

Beyond this range, the spectrum consists of infrared wavelengths and is invisible to the human eye. As noted above, below the 400 nanometer range the spectrum is also invisible to our eye and it's this portion of the spectrum that contains the cosmic, gamma, x-rays and ultra-violet wavelengths. And since 'Black Light' is below the visible spectrum, it cannot be seen by the human eye, nor does it contain any of the color wavelengths to be reflected back to our eyes, so everything will look quite drab (gray or black). And besides, the visible spectrum regulates the biological clock in animals and plants. Therefore Black Light does not serve any useful purpose in aquaria, and it can cause damage to your eyes.


Decades ago I gave thought to lighting several aquariums in my home with a skylight. The more I looked into the possibility, the less appealing it became. Besides questioning the quality and quantity of the light passing through skylight material, there was the expense of installing the skylight and seasonal temperature problems related to such an un-insulated area. After looking at all possibilities it was my opinion it simply became 'far' more cost-effective to stay with lighting systems and pay my electric bill every month!

Then, in the early 90's I had the opportunity to meet the owner of a company known as 'The SunPipe Company.' These 'pipes' were actually tubes of light-weight flexible aluminum material that came in two diameters, 13 inches (32.5 cm) or 21 inches (52.5 cm). They were internally mirrored, and it was claimed could provide over 1500 watts of light on sunny days, 200 to 900 watts of light on cloudy days with no adverse effect on heating or cooling. And once installed through the roof, it was no different from a skylight, except for the tremendous increase in light. There were also options such as the SunScoop and Light Regulator. The SunScoop, mounted on the top outside of the tube end, collected light from various angles and reflected it downward and was said to increase light by 170%. The Light Regulator acted like a light switch and simply would "turn off" the light by closing an internal door.

The product reignited my skylight thoughts and considered installing three of them over the 320-gallon tidal/reef system I had at that time. But unrelated problems prevented me from doing so, but my employer at that time liked them well enough to install two in an enclosed room with no windows. They were useful to the point that no lighting system had to be switched on every time the room was entered during the day, yet for studying the blueprints stored there, ceiling light fixtures where still used. Bottom line, they rendered light that was equal to what could be produced by fluorescent lamps of similar spectrum/intensity. That, if anything, would make them useful for a fish-only system during daylight hours on anything but rainy days. Yet supplemental nighttime lighting would still be needed if desired, as would probably be the situation with any form of skylight.

Unfortunately in some ways, products such as these did not catch-on for use in the aquarium hobby/industry, but nevertheless, I came away from this experience with the thought that products like these could be used in local pet shops during much of the daytime to help reduce general lighting costs. In fact, products such as these are still available.

Aquarium Lamps

A very long time ago the hobbyist had a choice between a simple incandescent lamp and a simple incandescent lamp! Then came the fluorescent lamp and choices widened. Now there's metal halide, mercury vapor, high-pressure sodium, a wider selection of fluorescent lamps, and LED lamps. To further complicate this whole situation, what works for one aquarist may not be exactly what another aquarist needs. Since there's nothing like doing it right the first time, and 'lamps' are the focal point where lighting parameters are concerned, lets first take a look at two of the more common forms of aquarium lamps – fluorescent and metal halide lamps. Then proceed to others of interest, such as the newest form of aquarium lighting, Light Emitting Diodes (LED's).


The fluorescent lamp generates light by sending an electrical arc through its tubular-shaped enclosure that in turn excites various phosphors that line its interior tube surfaces. When the phosphors fluoresce they emit light, which depending upon the blend of phosphors, result in particular wavelengths/color of light (spectrum). Before the tube is sealed, air is evacuated and usually replaced with argon, an inert gas and a drop of mercury. All readymade fluorescent fixtures have a ballast, now mostly an electronic ballast that steps-up household voltage to the point where it can vaporize the mercury, which then in turn generates enough electrons to excite the phosphors lining its interior lamp surfaces. There are many different tube lengths, diameters and endpin arrangements, so attention to this aspect is needed when selecting replacements. This is a far more electrical efficient process than what is found in conventional incandescent lamps, and with less heat generated. Their glass enclosure also eliminates harmful UV light from escaping; yet some UV A & B may still be emitted. But keep in mind, those germicidal fluorescent lamps used in UV sterilizers have no interior coating, therefore most of their UV is emitted, which is a good thing as their purpose is the kill small organisms passing close to their surface.

As fluorescent lamps age, their electrode begins to wear and fewer electrons are produced. Also, its mercury content becomes diminished by certain chemical reactions and its phosphors begin to deteriorate. In fact, many can lose as much as 40% of their intensity in their first year of use. And when these actions progress far enough the end of the tube will usually darken. Even though lamps may still appear to work when beginning to darken at their ends, they should be replaced with new lamps, especially when used for aquariums containing animals needing quality spectrum and intensity.

The diameter of these tubular (T) lamps is determined by dividing its following number by 8.

The common T12 fluorescent lamp is 1.5 inch (3.75 cm) thick or 12 – eights of an inch in diameter, and became quite popular with aquarists in North America during the late 80's and 90's, and in some situations are still used as they are less expensive than new thinner designs. There were and continues to be available three types: regular output/wattage (RO), high output (HO), and very high output (VHO). In the 90's, before electronic ballasts became popular, heavy and hot running separate tar impregnated ballasts were required, and the regular wattage lamps required the 430 mA ballast. The HO and VHO lamps, which provided higher light intensity than the regular wattage lamps required special ballasts, with the HO lamps needing the 800 milliamp (mA) ballast and VHO a 1500 mA ballast.

And depending upon system goals, T12 lamps such as the G.E. Chroma 50 and Chroma 75 RO lamps that are used in different commercial activities, are still quite useful for some aquarium uses. The spectrum in the C50 is late morning, and the C75 about mid afternoon, which makes these lamps quite useful over fish-only aquariums where great intensity is not required. In fact, they are very inexpensive when compared to similar spectrum lamps made especially for aquarium purposes!

Because certain spectrums are important to reef keepers, I should briefly touch on the 'Growlux' lamp. - For years, aquarists thought that if the Growlux fluorescent worked for their houseplants, it should do equally well for the plants and animals in their aquarium. They were right about its use in freshwater aquariums, as the lamp provides excellent spectrum for true plants and also enhances the colors of most fish. Even in seawater aquariums, the Growlux lamp can provide adequate viewing conditions. Yet, it was designed to give the houseplant what it needs, a much higher red band wavelength. That is why the lamp has a reddish tint when lit. I've used and will continue to recommend the use of Growlux lamps on freshwater aquariums, as they do a great job. But different lighting requirements are in order for marine aquariums. Keep in mind many of the corals that interest the marine aquarist have existed in the oceans for many thousands of years at a depth that does not receive the red portion of the visible spectrum. Nevertheless, these lamps would suffice for an algae turf scrubber/macroalgae refugium.

Today, the industry has mostly shifted away from using the T12, with smaller diameter tubes such as T8 (eight eights of an inch/2.5 cm), and the T6 (six eights of an inch) and T5 (five eights of an inch) lamps filling many aquarium needs. Add to this small electronic ballasts that can handle multiple and varying size output tubes, and aquarium fixtures have diminished in size, yet have grown in efficiency and light output.

Another addition to the aquarium industry has been the Power Compact Fluorescent Lamps (PCL) or sometimes simply referred to as the 'compacts' by aquarists. These small diameter lamps (T5) use smooth or spiral shaped U-shaped tubes that can doubled the light rendering 'area' making them ideal for small aquaria, especially where photosynthetic corals are being maintained. With low profile hoods, more energy efficient operation, and lengths varying from 7 inches (17.5 cm) to 34 inches (85 cm) that vary in intensity from 9W to 96W, they have been widely accepted by hobbyists. Moreover, in combinations of different intensity and spectrum they can also result in more quality light and less heat radiation than most other type lamps, yet their cost is still somewhat pricey. Endpin arrangements are now available in either Japanese or Panasonic, i.e., square pin arrangement or the European straight pin arrangement, which is comparable to the Philips brand. Of course there are also those with an end that can screw into an incandescent lamp socket, such as the type now being used to light some areas in homes or small commercial spaces, such as closets.

As mentioned above the choices for fluorescent lamps have grown with slimmer T8, T6, and T5 lamps providing for more light intensity with less energy consumed. And when combined with electronic ballasts, tend to have less spectrum shift during their lifetime than the previous T12 lamps. And if constructing one's own lighting hood, be sure to select the proper electronic ballast, as an incorrect choice may under or overdrive the lamp reducing its lifespan and/or spectrum. Check with lamp manufacturers for their recommendations.

T6 (and T5) lamps can actually replace T12 and T8 lamps in fixtures because they have the same bi-pin end (G13 base). Furthermore, they use the same ballasts and are found in common tube lengths, e.g., 24, 36 and 48 inches, and are available in RO and VHO forms. They have a slightly thicker glass making them more durable, operate at slightly lower temperatures and are even available in a 'curved' form that will fit the bow-shaped aquarium! They are presently being seen as the replacement for the T8, which has been very popular in Europe and gained much popularity in North America.

As for T5 lamps, all use the mini bi-pin end and are not interchangeable with other forms of lamp equipment. These and T8 lamps come in RO and HO forms, with the T5 maintaining a more superior light output over time than the T8 and the T12, possibly due its lower mercury content than these two other type lamps. T5HO lamps are available in 2, 3, 4, and 5 foot lengths having 24W, 39W, 54W and 80W capabilities. There is also the circular 55W lamp that is commonly used in various household areas. They also need special ballasts; therefore those used for T12 and T8 replacements will need new ballasts. Again, if constructing your own light hood, contact the manufacturer for their advice as to ballast needs.

Where fluorescent lamps and metal halides are combined in one fixture the T5 may be better suited than other type fluorescent lamps as they normally operate at a higher temperature, about 95°F/35°C, than do other forms of fluorescents such as the T12 and T8's which have a preferred operating temperature of about 77°F/25°C. Therefore, in confined enclosures where airflow is little or nonexistent, T5's might be a better choice when combined with metal halides as their performance and lifecycle may not be overly impacted as much as would T12 and T8 lamps.

And the choices continue, as there is now what are called Super T8's. When combined with special high-energy electronic ballasts they can reduce energy consumption by about 20% over that of regular T8's and produce more light/lumens per watt. They do cost more, and whether or not cost-effective in the long run is still unresolved, at least as far as I know.

Another popular fluorescent lamp coming in various sizes and wattages is the Actinic Lamp, which solely delivers a spectrum in the heavily blue range of 420 - 480 nm. This lamp is used to supplement other lamps on the aquarium that may be insufficient in this range or to provide a sunrise or sunset photoperiod by having them turn on prior to the systems main lamps and stay on for a short time after the main lamps shutdown.

Furthermore, some aquarium lamps are advertised as multi-spectrum, wide-spectrum, broad-spectrum, etc. Yet, the only way to tell the quality of the spectrum will be to look at the lamps individual 'Spectral Power Distribution Curve Chart,' as it illustrates where the lamp's wavelengths peak along the visual spectrum. Kelvin temperature/rating is the important aspect here. If the dealer/distributor cannot supply this information, try the manufacturer. If unsuccessful, look elsewhere for another brand lamp! In fact, this is true for all types of aquarium lamps.

For those making their own fluorescent fixtures, keep in mind lamp intensity can be greatly increased by simply lining the top half of the light hood with reflective heat resistant material, e.g., aluminum foil or mirror-like Mylar. Even white paint will help. In fact, there are some fluorescent lamps having internal reflectors built into the upper 180-degree surface of each lamp. This does add some cost to the lamp, but can result in 40% greater intensity in their downward projected light.

For those using fluorescent lamps of any kind, you may find the following lamp replacement schedule helpful: regular wattage - every 12 - 16 months; HO - every 10 to 14 months; and, VHO - every 6 - 10 months. And for your safety and that of lengthening tube life somewhat, HO and VHO lamps should be equipped with waterproof end caps. I also recommend writing on the tube with a permanent marker the date the tube was installed.

There's no doubt fluorescent lamps will continue to see improvements in the coming years and remain in many situations a perfectly acceptable way to light some aquariums. Yet, the cost associated with HO, VHO, special ballast's, end caps, and their replacement schedule can make them more expensive in the long run than metal halides.

Metal Halide

Metal halides (MH), including mercury vapor and high-pressure sodium lamps, are considered High Intensity Discharge (HID) lamps. They use a small tube-shaped bulb, called the 'arc tube,' to generate light. This tube contains a metal, e.g., sodium for sodium halide lamps, mercury for mercury halide lamps or metallic halides for metal halide lamps that when vaporized by an electrical arc passing through them render an intense light having the spectral qualities generated from that form of 'metal.' That differs from incandescent lamps that simply heat a filament.

Mercury and sodium HID lamps generally produce an intense bright light by peaking in the green/yellow range, i.e., 550 - 600 nanometer range. Due to their low cost these lamps have been mainly used for lighting areas such as parking lots, streets, landscaped areas, gymnasiums, etc., where 'bright light' is needed. Where most aquarists are concerned, sodium and mercury lamps render an unnatural washed-out color of target organisms and aquarium aquascaping. Additionally, they produce a lot of heat for the light produced and some unwanted A and B range ultraviolet radiation (UV). They may be good for freshwater aquariums, but not marine aquariums.

Aquarists have found metal halides far more capable of producing broader spectral needs, including the blue and red wavelengths needed for photosynthesis. As this style lamp popularity increased, manufacturers have engineered an array of different metallic mixtures to satisfy a wide range of needs, especially those of marine hobbyists. This has resulted in a dizzying array of claimed spectral choices/qualities, which in turn has led to an increase in conjecture amongst aquarium hobbyists and lighting professionals as to their claims/results. And with no two lamps perfectly alike, even those in the same batch (something like snowflakes in a snowstorm), claimed specifications per lamp model should only be considered a good 'yardstick' for said defined lamp model. Furthermore, with an array of installation possibilities, especially if one is constructing their own lighting hood, the resultant spectral wavelengths leaving a lighting fixture can vary even further. The quality of their reflective enclosure is also something to keep in mind, as mirror-like surfaces reflect much of the upward traveling light back downward.

To somewhat further complicate this style lamp selection, the physical size and shape of some MH lamps has changed. It was that all had their light emitting arc tube further protected by a larger surrounding glass enclosure. Now, the arc tube itself, without the larger outer surrounding glass globe is being marketed as single or double-ended High Quartz Iodide (HQI) lamps. Without the secondary glass enclosure, its quite important these style lamps be protected from splash and be installed in a lighting hood that has a sheet of glass between them and aquarium water. Furthermore, the glass will protect organisms in the aquarium from possibly incurring UV damage. In fact, those were the reasons for the secondary enclosure, i.e., to somewhat protect from splash and undesirable UV wavelengths! But production costs with this style lamp could be trimmed and lighting hoods of less height utilized, and when combined, reduce final product cost. All in all, these are excellent quality lamps and if used properly, can provide first-rate results. Be sure to read the topic below on Ballasts, as there are some very defined aspects to their selection when it comes to powering this style lamp.

Overall, aquarium MH lamps are available in wattage's from 100W to 1000W and have useful color temperatures in the range of 5500K to 20,000K. The 5500K lamp is equal the color of sunlight at the noon hour, and the 6500K is equal to a mid-afternoon color temperature. Keep in mind lower Kelvin lamps can also be supplemented with separate actinic-like fluorescent lamps as mentioned above. The 10,000K and 20,000K are equal to late afternoon temperatures. Since blue and white light generates the best coral growth, the 6500K lamps is a better choice than 5500K lamps for reef aquariums, with those in the 10,000K – 16,000K range my favorite. Yet keep in mind when looking directly at a 10,000K lamp they render a very intense white light to the human eye, however aquarium animals sense its higher blue content. The 20,000K lamps also produce excellent results with photosynthetic animals, yet the aquarium environment looks overly blue to the human eye when compared to 10,000K lamps.

Another factor to take into consideration is the heat produced by these style lamps. If mounted in a light hood, exhaust fan(s) need to be installed so outside air is drawn 'through' the enclosure during operation. Air drawn in is better than air pushed into the hood, as lamp temperatures stay more even throughout the length of the hood. Lamp distance above the surface of the aquarium water depends on whether they are enclosed in a cooled hood, or simply hanging above the aquarium in an open pendant-type fixture. When 'enclosed' with cooling airflow, the lamp(s) can be placed to within a few inches (7.5 cm) of the water surface. In hanging fixtures, 12 to 18 inches (30 - 40 cm) above the aquarium may be necessary depending upon wattage and amount of radiated heat.

But do keep in mind, the quantity of light decreases by one-forth every time the distance from the lamp/source doubles. Therefore, the further away the light source, the less quality light is reaching the organisms in the aquarium. Therefore, thought must be given to that distance, especially with pendant fixtures. In some situations, the aquarium will need a chiller because of the amount of radiated heat from these sources of light.

Wattage/PAR selection depends upon the depth of one's aquarium and what invertebrate species is being maintained. If using wattage as a selection factor, on the average the under 20 inch (50 cm) high reef aquarium can utilize 175W lamps. The 20 to 30 inch (50 - 75 cm) high aquarium may want to utilize 250 to 400W lamps. And anything over 30 inches high, 400W lamps may be the better choice, but again this all depends upon the need of photosynthetic animals being maintained. Furthermore, lamps should be spaced about 10 to 18 inches apart, and depending upon the type/brand used, replaced every 12 - 18 months. Again, consider their wattage as a good yardstick, with PAR a far better selection factor.

Another 'wattage' rule-of-thumb used when it comes to intensity is the following;

  • For the average reef aquarium - 4 watts/gallon for aquariums under 20 inches high, 6 watts/gallon for reef aquariums between 20 to 30 inches high, and 8 watts/gallon for reef aquariums 30 to 36 inches high.
  • For lighting the fish-only aquarium - about 2 - 4 watts/gallon depending upon depth.

One further discussion topic concerning MH lamps is the little bump, or nipple that occurs on the arc tube. This is where the gas is injected into it, and then sealed. Some aquarists say that depending upon the position of the lamp, i.e., the nipple facing upwards or downward, a different color spectrum is noticed. All in all, it has been found there is far too may variables to take into consideration, such as lamp age, type/brand/wattage, operating temperature, etc., to state one way or the other that its position has an effect on resulting spectrum.


Aquarium 'moonlights,' e.g., LED (Light Emitting Diode) or fluorescent 'actinic' lamps that emit a blue spectrum near 484 nanometers actually duplicate the spectrum/light coming from the moon. Equipping one's aquarium with 'moonlights' brings the overall lighting timeframe (24/7) in tune with the wild where all shallow water animals experience the changes in light intensity. Not only does the utilization of this form of lighting reduce animal stress for both fishes and invertebrates, it also provides a more pleasing environment for nightly hobbyist viewing!

As to LED equipped moonlights (see below for a discussion on LED lamps), my first experience with them came in the late 90's/early 2000's. While consulting with BrightLights Technologies at that time, which was the first company that I know of to bring these lamps to the aquarium marketplace, I was among the very first to utilize these lamps on aquariums. In fact, can remember some very late nights sitting in front of my 125-gallon reef aquarium watching animal activity not seen during the daytime. Also remember trying several different 'polite' ways to make occasional guests realize it was time to go home, as my moonlights came on about 10:30 at night and their questions about activity in the now 'moonlit' aquarium sometimes seemed endless!

When it comes to selecting lunar/moonlights, LED lamps or an actinic fluorescent lamp fixture can be utilized to create the moonlit timeframe. As to LED lighting technology, it generates very little heat, e.g., probably only slightly above the temperature of your normally maintained tropical aquarium, and the lamps should last at least 50,000 hours without any significant decrease in spectrum or intensity. And past information on these lamps had them lasting up to 150,000 hours with only minimal reductions in their spectrum and intensity! In fact, I'm still using the LED 'review' preproduction moonlight model called 'MoonBeam' for 10 hours daily that was sent to me over 15 years ago! Of course, actinic fluorescents can't make that statement, but I've used them on some past aquariums also quite successfully in my opinion.

LED moonlights also provide one visual benefit fluorescent lamps do not and that is pin-point focus of its light energy which results in glitter lines on the substrate during the moonlit timeframe, as seen in the wild. Fluorescent lamps are designed, because of their length to spread out its intensity/spectrum thereby distributing its light over a wider area, therefore do not render a more focused light shaft capable of producing glitter lines.

If there is one thing about the moonlight timeframe that should be kept in mind, it should not in my opinion be used every day of the month. The actual lunar cycle is 15 days of moonlight and 15 days of darkness. Therefore, moonlights in your aquarium should only be operational for half of the month if wishing to actually replicate that in the wild.

Light Emitting Diode (LED)

These are basically tiny solid-state light bulbs, which are made-up of diode chips made from semiconductor materials. They are then encased in plastic or silicone lenses making the lamp itself shockproof, both mechanically and electrically, and also impervious to most environmental conditions such as moisture. When electrical current is passed through the semiconductor material, the movement of electrons through the element causes it to give off light. In fact, a greater percentage of electrical current goes to generating light than in other types of lamps, and different semiconductors provide different colors.

And maybe that's as technical as I should get as I'm far from an expert in this matter, as the technology surrounding this device has advanced greatly since aquarists saw the first blue 'moonlight' discussed above. Nevertheless, some lighting companies foresaw very low energy, long lasting LED fixtures for aquariums as the lighting wave of the future. But the path has been difficult and even though these little lamps can last 50,000 to well over 100,000 hours and consume 80 - 90 percent less energy than regular lamps, useable color rendition and intensity for overall aquarium usage has taken a lot of R&D, besides $!

Its well known that LED's are extremely bright when looking directly at the lamps, making them great for sign applications and requirements like traffic lights, television screens, flashlights, or various lighting effects on some autos. Yet focusing the light rendered onto a surface at a reasonable depth and at adequate intensity and spectrums for viewing and animal photosynthesis has been a difficult path. But now with far improved technology, LED light fixtures are beginning to replace fluorescent and MH equipped lighting fixtures. In fact, light output of LED's, measured in lumens per watt, has now exceeded that of fluorescent and metal halide lamps, e.g.,

Fluorescent - 45 - 100 lm/W

Metal Halide - 100 - 110 lm/W

LED - >150 lm/W

Yet keep in mind 'lumens' is a parameter, as explained earlier in this chapter, that serves no useful purpose in aquaria as its geared to what the human eye perceives, which is more sensitive to mid range colors in the visible spectrum, i.e., green and yellow. Nevertheless, overall it's an indicator that technology continues to move ahead.

Probably the first entry into the overall needs of aquarium lighting was the Solaris lighting fixture from PFO Lighting Inc. in 2007. These fixtures, which blended light from white and blue LED lamps in a useable parameter, became available in lengths from 12 inches (30 cm) to 72 inches (180 cm), and were only about 8.5 inches (21.25 cm) wide with a height of about 3.75 inches (9.4 cm). They were also capable of 'dialing' in a color of light ranging from 6500K to 20,000K, and there was also a built-in timer to control sunrise, sunset, daylight hours, cloud cover, and also its 'moonlights,' which could produce a 28 day moon cycle if desired! And since heat, such as what MH's produce, was not a major factor with LED lamps, it appeared that some aquariums equipped with LED lighting hoods might not need a chiller! Unfortunately legal problems prevented the company from flourishing even though their fixture was greeted with much enthusiasm/compliments.

All in all, the aquarium LED future is upon us, and various brands/models are readily available! And competition will increase for your lighting dollars, which is a good thing for all hobbyists as it helps to increase their efficiency and bring down their cost. However, selecting a fixture that will suit the needs of 'your' aquarium can be confusing for many reasons, e.g., specifications are not clearly understood or made available by some fixture manufacturers, therefore making it a somewhat expensive gamble that the selected unit 'will' adequately fulfill the requirements of the animals in your aquarium!

So what are those 'specifications' or attributes the shopper should be aware of? Probably the first should be the light requirements of the animals in their aquarium as to their PAR requirements, which includes the red and blue wavelength that are vial for photosynthesis. Bear in mind lumens conversion to PAR is not possible without knowing the exact spectrum of light being emitted, which is a complicated task only suited for lighting engineers. And since there are animals that require a certain amount of light (spectrum and intensity) to remain healthy, they can be fitted into groups and a more useful 'PAR' range assigned that will most likely meet their light requirements.

Therefore, these are among the questions to ask oneself if shopping for a LED fixture: Are there shallow water/fringing reef stony corals that require intense light to remain healthy/colorful, such as a PAR value of about 400 - 800+? Are there soft and stony corals/other animals liking medium light, such as a PAR value in the range of 100 - 400? Are there low light corals, such as mushrooms that prefer a PAR value of about 50 - 100? Once that is resolved, the aquarium depth of these animals should be noted since LED lamps will deliver a cone-shaped shaft of light to specific depths, which can be related to specific PAR values (a graph/chart depicting this shaft of light and its PAR values at different depths should be provided by the manufacturer - hopefully), which in turn can give the possible buyer a good idea of just what value of light (PAR) the fixture will render and to what depths 'and' just how wide that area of coverage will be at different depths.

Then, animals needing those levels of PAR can be placed in the aquarium within those depths and width/footprint areas. And because these LED fixtures do not radiate heat (infrared) or UV and have protective lens coverings, they can be mounted very close to the aquarium's water surface somewhat bringing that 'cone' of delivered light deeper into the bulk water of the aquarium.

Once intensity/spectrum and coverage of the light delivered is ascertained, and if the budget allows, look for fixtures equipped with microprocessor controlled circuitry and LCD illuminated controller panels that can possibly program moonrise, moonset, phases of the moon, color/quality of the delivered light so its also able to suit individual human eye preferences, cloud simulation, and automatic dimming or intensity increases (sunset/sunrise intensity periods), as they add to the overall viewing pleasure and no doubt health of the aquarium's inhabitants. Finally, be sure the delivered light is also pleasing to the human eye, as some combinations of different colored LED lamps in low end/low price models do not result in what can be called a satisfactory visual affect.

And yes, there's more to it of course, as there are different wattage LED lamps (generally 1 - 3 watt lamps, with higher wattage 5 watt lamps now available in some units), different color producing lamps (blue, white, green, cyan, red and ultraviolet and no doubt more to come), assemblies where the end user can change out lamps (thereby tune the overall color of the delivered light/replace worn out lamps), different methods to alleviate the heat produced (passive or active heat sinks that affect longevity of the lamps), different blends of the color lamps themselves (yet mostly white and blue are used in today's fixtures, yet some top of the line models also have red and yellow), and different types of lens coverings/reflective surfaces to focus the light rendered and protect from moisture, etc. And there's also screw-in LED bulbs that can serve as a replacement lamp for mogul-based MH lamps. There's also LED lights that look exactly like a long fluorescent lamp tube, yet have a string of connected LED lamps inside the glass tube, with each tube containing its own ballast! And they plug into common fluorescent end fittings!

And to possibly complicate selection somewhat, or meet specific lighting goals in certain areas of the aquarium, there are LED lamped spotlights and/or strip lights besides the all-encompassing overall fixture/hood. Each has variants that should be researched prior to purchase depending upon one's lighting goals/needs.


LED's use about 85% less electricity than do other forms of lighting equipment!

LED lamps far outlast fluorescent or metal halide lamps - with 50,000 hours about the norm, verses only 3000 hours for fluorescent or metal halide lamps! Lamp replacement alone is a tremendous cost savings!

LED's produce far less heat than metal halides!

LED's produce far more light for far less applied energy --- 100 watt LED = 300 - 400 watt metal halide!

All LED light is directed downwards into an inverted 'cone/funnel' shaped area, as none is wasted as with fluorescent or metal halide lamps which disperse a good portion of their light sideways and upwards! (Most LED lamps disperse light at 90 degrees, yet as of 2015, 120 degree lamps are becoming available, providing a wider degree of light in the aquarium.)

LED technology has progressed so fast that built-in fixture computers make programing various blends of light colors, various intensities (PAR) for various hours of operation extremely simple!


No matter what type lamp your aquarium fixture may be fitted with, 'ALWAYS' before purchasing it, understand your 'Kelvin' lighting needs, then ask to view the fixture's PAR depth charts. All quality brand lamp/fixture manufactures should supply spectra-graphs and PAR charts. If not, look elsewhere!


Did you know - LED fixtures not containing seals of safety approval from reputable testing authorities are generally not covered by one's home insurance should they catch fire, nor would the damage it caused!

There's no longer any doubt that LED's can meet the needs of the animals in the aquarium and are far more economical than fluorescents and/or metal halides in the long run! Do your research on this form of lighting and if at all possible actually see the unit in operation before selection is made.

Halogen Lamps

With new forms of lighting technology or even updated old technologies, the march towards new lamps and equipment continues, as it should. And it seems like there's not a week that goes by without someone or some company applying some form of technology to aquarium use. In fact, the use of Halogen lamps, which are used both in home lighting track systems and/or businesses such as jewelry stores to highlight the items for sale, is one that recently caught my eye. Their internal reflector is capable of focusing a beam of light a considerable distance, thereby 'highlighting' the items being targeted. Yet, their color rendition is poor, mostly a yellowish color, yet understand even that is undergoing improvement. And even though useable in some limited situations, possibly in small aquaria to emphasize a particular item, their use is extremely limited. Overall they should be considered as having potential for future applications, but as of now something few hobbyists will employ.


The ballast determines how much energy the lamp receives, thereby regulating its efficiency and longevity. Where aquarium light fixture ballasts are concerned, a good saying would be, 'you've come a long way baby.' A decade or two ago only brick-like tar ballasts accompanied most aquarium light fixtures. They were heavy, ran hot, and they themselves consumed much energy. In fact, some of the larger ballasts I had on my old reef systems were so big they could have made good boat anchors at some point in their existence! And in those days, only certain ballasts would correctly power certain lamps, therefore some research had to be accomplished before lamps and ballasts were combined, as aquarists in those days constructed most of their own lighting systems. Today, most ready made light systems, whether fluorescent, MH, or LED incorporate small, cool running electronic ballasts, doing away with much of the need to make separate component choices.

Nevertheless, these 'bricks' still are used in some areas, so thought it wise to make a few comments about them. - Keep in mind they get hot, very hot in some applications, therefore they should be located in an area having good air exchange, as some have internal heat switches and can shut themselves off if they get too hot. Putting them inside a cabinet or in a position where they do not get good air circulation may cause the internal thermal switch to shutdown the entire lighting unit, and it may be a longtime before it cools sufficiently to restart the system! Consider elevating them on a couple of cement bricks/wooden boards or placing the ballast on the floor where there is some air circulation. Heat will then rise up and away from the ballast. If possible make sure the ballast is located far away from the high humidity area generally found under the aquarium to prevent their metal covers from rusting.

Where fluorescent fixtures are concerned, most now come with electronic ballasts and besides the above-mentioned benefits they also provide a somewhat greater efficiency/efficacy than do the old fashion tar bricks. In addition, single ballast units can drive a multiple lamp fixture, and if the aquarist decides to upgrade the fixture from Regular Output (RO) lamps to Hi Output (HO) or Very High Output (VHO) lamps, some can sense the need of the different style/wattage lamps and adjust power output accordingly without itself being upgraded. Some are also very capable at 'dimming' these lamps at chosen timeframes. By allowing a ramp-up or ramp-down timeframe, a sunrise or sunset photoperiod can be achieved. This mimics nature in the wild; a goal of many hobbyists, and in some situations enhances the spawning capability of some species. Keep in mind the totally on/off lighting photoperiod is stressful to aquarium inhabitants. You may want to visit for more information.

Electronic ballasts are also becoming available that automatically select the correct input voltage, thereby accepting any line voltage between 120 – 277V. Therefore, they can be utilized in a wide range of areas throughout the world without concern as to their input voltage. This should reduce the manufacturer's cost, as one style ballast or lighting hood can be produced and shipped globally, which should have a positive affect lowering their retail cost.

All in all, if the goal is to construct one's own fluorescent light fixture, its wise to contact the manufacturer of the preferred lamps and get the needed data as to the correct ballast to power them. Yet, in my opinion, it no longer seems necessary to construct one's own fluorescent lighting fixture, as there are so many different and well-engineered pre-assembled fluorescent light hoods available.

And if constructing a metal halide lighting hood be aware the choices for lamp ballasts is far more daunting as the supply of lamps themselves is growing, and appear to have very specific power needs that if not supplied adequately will cause the lamp to render a poor spectrum and/or negatively effect its lifespan (usually both). As an example, it has been found that Asian produced lamps will not operate correctly on the electronic ballasts designed for European produced metal halide lamps. Furthermore, ballasts are being produced by some aquarium companies with a 'HQI' designation to power lamps coming primarily from Germany, e.g., the double ended 150W and 250W, and the 400W single end lamps. Keep in mind 'HQI' is a Trademark of the OSRAM GmbH Company in Germany and these so-called HQI rated ballasts from 'other' manufacturers have shown in some cases to be nothing more than standard ANSI ballasts and not 'specifically' design for these German lamps. Whether or not actually suitable remains debatable for the experts to resolve, but a lesson no less for the hobbyist, as one should carefully research the needed ballast to power the chosen lamp.

Finally, where compatibility between lamps and ballasts are concerned, do not simply accept what is seen in advertisements and/or on their labeling. Let me leave you with these words of wisdom when it comes to selecting ballasts to power particular wattage and style metal halide lamps - Research, Research, and more Research! And a good place to begin this research is on the following website; Visit Website, which is constructed by the American aquarist Sanjay Joshi, and which provides the specifications and properties of various metal halides and ballasts along with answers to other lighting equipment questions.

Lighting Points of Interest (POI)

Over the past decades I've collected what could be called 'points of interest' when it comes to the subject of 'light.' They cover a wide area of lighting aspects and have numbered them, then related most to situations that may develop in aquaria. Hopefully, you'll find some helpful when choosing a lamp or fixture, or at a minimum, at least interesting. Just keep in mind many of them are quite dated!

1. The photometric unit used to measure the total brightness the human eye sees from a light source is called the 'lumen.' Each lumen is equal to approximately 10 footcandles. (One footcandle is the light seen by the eye from one foot away from a single candle.) Bear in mind this is not the energy received by the target organism.

2. One lumen falling perpendicularly on the surface of one square meter is called 'lux.'

3. The light energy from the Sun falling on one square meter of ocean surface at noon on a clear day can exceed 100,000 lux.

4. Light is absorbed by seawater therefore limiting how much intensity and spectrum will be available at a given depth.

5. Within the first few meters of seawater the ultra-violet and red wavelengths are absorbed. In the next five to ten meters the brighter color's, i.e., orange, yellow and green are absorbed. Only blue remains to penetrate down to about 100 meters.

6. Lumens from a given light source decrease in proportion to the square of the distance between the source and its destination. This simply means the quantity of light or lumens decreases by one-forth every time the distance from the lamp/source doubles.

7. A glass or plastic aquarium cover between the light source and its destination can reduce/alter both intensity and spectrum.

8. Water surface movement reduces light transmission.

9. The types of material/color of light reflectors, e.g., the interior of the light hood, will have a bearing on the total amount of light to reach its destination. Mirrored surfaces are the best at reflecting light.

10. Dissolved Organic Carbon (DOC) scatters light waves, thereby reducing intensity. Excessive use of additives can also skew light transmission, possibly changing it more to a spectrum (red) preferred by algae.

11. Some fluorescent lamps lose approximately 40% of their intensity during the first year of their life span.

12. The average photoperiod in nature is sixteen hours of light and eight hours of darkness. The most intense period of light is between 10am to 2pm.

13. Efficient photosynthesis is dependent upon three factors: light intensity, CO2 concentration, and temperature (Moe 1989).

14. Intensity above 'light saturation' in some phytoplankton causes membrane damage and the subsequent release of intracellular material produced during photosynthesis (Fogg et al. 1965, Hellebust 1965).

15. Most of the photosynthetic organisms collected for our aquariums come from a depth of 20 to 40 feet. At this depth light intensity, depending upon various daytime conditions, ranges from 5000 to 15,000 lumens.

16. Most photosynthetic organisms have shown a remarkable ability to adapt to gradual changes in both spectrum and intensity.

17. Photosynthetic organisms, i.e., mainly corals and anemones, have a single-cell alga called 'zooxanthellae' living inside their flesh. These alga cells are a vital part of the animal's food chain. In fact, there is a symbiotic relationship where via photosynthesis these cells utilize some of the animal's waste products and in return provide a food source for its host.

18. Zooxanthellae may require more intensity than the macro or microalgae found in the aquarium or nature because zooxanthellae are imbedded in animal tissue.

19. The 420 nanometer wavelength closely aligns with the blue chlorophyll absorption peak utilized in photosynthesis.

20. Lamps such as the Philips Actinic 03 or any lamp mainly high in the blue 420 nanometer range cannot be rated in lumens.

21. Some invertebrate are able to signify UV irritation by closing tightly, usually referred to as coral burning, and/or emitting strings of mucus, swelling, or ejection of mesenterial filaments.

22. Photosynthetically Active Radiation (PAR) measures light intensity over the visible spectrum (400 - 700 nm), which is somewhat different from lux that reports the intensity of those wavelengths to which the human eye is most sensitive (largely the green wavelengths). PAR is reported in units called microEinsteins per square meter per second (μE/m2(sec).

23. Wherever there is life, there is light, even at the deepest portions of the ocean. However, the human eye cannot perceive it.

Lets now take most of the above purposely-numbered Points Of Interest (POI) and relate them to appropriate situations.

  • POI 4 and 5 - mention was made of seawater's ability to filter out various wavelengths (colors of the visible spectrum) and greatly reduce its intensity at lower depths. Normal wattage fluorescent lamps (RO), which generate weak light transmissions, can provide little more than an intensity found in 'very' shallow areas. High Output (HO), Very High Output (VHO) fluorescent lamps and metal halides are better suited for ninety percent of our photosynthetic organisms at aquarium depths greater than 12 inches. Keep in mind LED lamps are now surpassing the output of both fluorescent and metal halide lamps!
  • POI 15 - it was pointed out that most of the coral specimens we strive to keep in our reef aquariums come from a depth in the wild of about 20 to 40 feet. At this depth the intensity of light can range from 5,000 to 15,000 lumens during the most optimum time of day. Therefore this is the average intensity we should strive to attain at the depth of the photosynthetic corals in our aquariums, not just at the surface of the aquarium.

    Taking this POI into consideration, in the late 80's I tried to develop a way of figuring out just how much light would be needed for my 320 reef system, and decided it was necessary to begin with an average, i.e., 10,000 lumens, at the surface of the aquarium. To do that it was necessary to multiply the length of the aquarium by the width. My old 320 gallon reef system was 96 inches (240 cm) long by 30 inches (75) wide, or contained 2,880 square surface inches, or close to 1.9 meters. The 2,880 numbers were multiplied by 6.5, the number of lumens falling upon one square inch of surface area of one square meter 'at' intensity of 10,000 lumens. The result was 18,720 lumens. This meant I would have to produce a total of 18,720 lumens to have intensity equal to 10,000 lumens over the physical surface area of the aquarium.

    Depending upon the efficacy rating of the selected lamps, which is their ability to convert electricity to light, the necessary wattage could then be figured out to accomplish the total of lumens over a given area. Bear in mind this only represents a possibility of whether or not the overall '10,000 lumen' goal can be achieved by RO, HO, VHO fluorescent lamps or metal halides.

    Efficiency (efficacy), the lamps initial lumens divided by the lamp's wattage, are now multiplied by 0.5, a standard used to take into account the losses mentioned in POI #7, 8, 9, 10 and 11 (Spotte 1979). At that timeframe an average 175 watt metal halide lamp had an efficacy rating of 86. Multiply 86 by the loss factor (refraction coefficient) of 0.5 and the result is 43. Now take the 18,720 lumens number and divide it by 43 for the number of watts needed to produce the desired lumens. The wattage required is 435 watts. That would require three, 175W metal halide lamps to meet a surface rating of 10,000 lumens. Keep in mind that this is at the surface only and this personal 'equation' is only presented here because it seemed to adequately meet my aquarium lighting needs.

    That was then and currently would suggest staying with PAR ratings, and look back at the discussion for what PAR levels were thought to be of value for different coral species in the above LED discussion.
  • POI #6 - mention was made that intensity decreases in proportion to the square of the distance between the animal to be illuminated and the light source. Even in an average depth aquarium, i.e., 18 inches, light intensity is going to fall off rapidly as it reaches into its lower levels. Since my 320 gallon aquarium was two feet deep it seemed I would need to quadruple the 18,720 lumen rating at the surface of the water to acquire approximately 10,000 lumens at its mid-point of depth. That meant a total of 74,880 lumens at the surface utilizing 1741 watts or about six watts per gallon. This simply meant the use of regular and HO fluorescent lamps were eliminated. That either left VHO fluorescent lamps, metal halides, or a combination of both.

    Taking into consideration POI # 6 and 16, and my ability to pay the electric bill, I decided upon four, 175 watt 5500K metal halides rated at 15,000 lumens each, mounted about 4 inches (10 cm) above the waters surface and four VHO Actinic 03 fluorescent lamps. Therefore, considering the lamp height above the water surface along with 700 watts of metal halide and 560 watts of Actinic 03 I felt confident I would be attaining more than adequate intensity in a well-managed system for most photosynthetic organisms. Keep in mind Actinic 03's are not rated by lumens and that is why I didn't include them in the above lumen total. It is more proper to look at their wattage rating. Wattage is energy and energy relates to intensity even if the human eye cannot perceive it.
  • POI #16 - the reason why many of us are successful at keeping many of the photosynthetic animals, however bear in mind it's the sudden and radical changes in intensity that often negatively effect the organism.
  • POI #12 - the photoperiod in nature is briefly described. As for nature's intense four-hour period, most intensity levels over aquariums are substandard in the quantity of its intense light. Therefore recommend five to eight hours of intense light depending upon the individual equipment/environment. The time of day for the intense lighting period can be reserved for the viewing hours.

    There should also be a sunrise and sunset period when only minimum lighting; usually actinic-type lamps/LED lamps are on so as to prevent shock to the animals when the main system lamps turn on/off. It could be a sequence such as: actinic fluorescent/LED lamps come on at 10am, metal halides come on at 3pm and go out at 10pm, and the actinic/LED lamps go out at 11pm. A nice added touch might be a slightly less intense 'moonlight' period of time where just prior to the evening fluorescent actinic/LED lamps going out, the 'moonlight(s)' comes on and stay on until daybreak.
  • POI #14 - a too intense light can cause oxygen poisoning. When deepwater invertebrate or even collected specimens left in poorly lighted conditions are subjected to too intense light, zooxanthellae can produce excess oxygen and poison the animal. First placing most newly acquired specimens low in the aquarium and gradually raising them over the coming weeks to their final position in the aquarium can avoid this.
  • POI #20 - lamps that render a dim light such as Actinic lamps have very low lumen ratings since the lumen rating is a measurement of what the human eye perceives. Therefore, using the wattage of these type lamps, as in the watts/gallon method, is the proper way to assess the value of these type lamps. Keep in mind photosynthesis occurs at the two dimmest wavelengths, at least to the human eye, of the visible spectrum, i.e., blue and red.
  • POI #21 - do not maintain deepwater specimens under UV emitting lamps. If not sure about the lamps' wavelengths contact the manufacturer. If necessary, shield/filter emitted light with forms of Plexiglas that will filter out all UV under 385nm. If this is not possible move the specimen to a lower level in the aquarium. Remember, color of the animal is not always an indicator of the animals' ability to withstand UV. Leather coral, e.g., Sarcophyton sp., have a brown pigment primarily from their zooxanthellae and can tolerate high levels of UV.

Lighting Summation

When it comes to lighting one's aquarium, spectrum and intensity must be its focal points. If either is insufficient, one's goals may not be met, and worse, some organisms may be lost and your investment in time and money wasted. And in quantifying these two factors, there's a widening array of technical data and claims to decipher, along with what seems like a never-ending supply of new lamps and fixtures to choose from. Because of that, a complete 'book' could be written on this subject alone, then not be up-to-date when finally published months later!

Nevertheless, it should suffice here to say if the goal is a fish-only aquarium, where in most occasions only enough quality light is needed to view the fishes, wide/broad spectrum fluorescent lamps might be a good choice. Nevertheless, LED lamps are not only sufficient; they are quickly replacing fluorescent lamps in the marketplace! Where reef aquariums are concerned, some invertebrate selections require bright light; therefore both spectrum and intensity are critical factors for long-term success. Fluorescent and MH lamps can still, as of 2014, still meet Kelvin and PAR requirements, but LED's are quickly overtaking them as the lamp of choice. Yet, as to which type lamps, their wattage/PAR/PUR ratings, and how many are needed, that's where discussing your needs with a local shop owner and/or being a member of a local aquarium society is invaluable, as someone with previous experience is worth far more than what can be read on labels or in advertisements.

Furthermore, this chapter can be considered a 'primer' for those entering the aquarium hobby, not a detailed assessment of aquarium lighting equipment. If you desire far more technical information, visit Sanjay's website mentioned above or an article written by Carl Strohmeyer titled 'Aquarium Lighting' at Click Here. Both sites are 'excellent' and should vastly broaden your knowledge on aquarium lighting!

And with the very wide selection of complete lighting fixtures available, some having internal cooling fans, high quality reflectors, electronic ballast(s) especially designed for the lamps in use, and in some cases several moonlights depending upon their length, it would be a far better choice than constructing your own lighting fixture. And one thing further about labels, purchasing products/equipment with the Underwriters Laboratory (UL) seal indicates it has passed stringent electrical safety testing, which can be really important to your safety, and those in your aquarium!

In closing, no matter what your choice of lamps or combination of lamps, always keep my lighting equation in mind:

Spectrum (Kelvin) + Intensity (PAR) = Success!


Lets now move to Chapter 6 and discuss and view some of the various construction materials and maintenance products that encompass getting the desired system up and running!