Reef Lighting By Luke


Reef Lighting:
The majority of corals, that the aquarist has access to, need light. If this one (seemingly) simple parameter is not met, these corals will wither away. Hopefully nobody wants to kill these animals (or at least put down $50 to do it). Those who are successful in this hobby have figured out reef lighting.
The first step to understanding lighting over a reef... is to understand all the terms that come with it. I will include the Webster’s dictionary definition then a more basic one (if necessary)
Lumen: “2: a unit of luminous flux equal to the light on a unit surface all points of which are at a unit distance from a uniform point source of one candle.” (Webster’s)
Alternate Definition: Measurement of light output. (The more lumens the more light.)
Lux: “a unit of illumination equal to one lumen per square meter” (Webster’s) (10.76 Lux in a lumen (Reef Aquarium Vol. 1))
Alternate Definition: Measurement of light output. (Again the more lux the more light.)
Kelvin: Webster’s does not define Kelvin (in terms of light but rather temp which is important to the light scale [see below]).
Alternate Definition: Measurement of light color. This measurement is one of the most important terms to understand. The Kelvin color scale ranges from 0°K on up. 0°K represents absolute zero. You are probably asking why temperature (the Kelvin scale) has anything to do with light? The Color scale is derived from a “theoretical ‘complete radiator’” (the Reef Aquarium Vol. 1). The idea is to record the color an object gets at different temps. Think of a nail being heated by an intense flame: first it glows red, then as it gets hotter it begins to glow yellow, then white, then blue. This is where the color scale comes from. But rather than a nail, this theoretical object is used instead. Thus the scale goes from red (in the low temps) to blue in the high temps. Certain Kelvin temps go through water better than others, certain temps react with corals better, certain ones grow algae better. Understanding what temps to use will greatly increase your success as a hobbyist. Here are some examples of Kelvin temps quoted from the Reef Aquarium Vol. 1:
“Approximate colour Temperature, Kelvin
Candle Flame: 1800
Incandescent bulb: 2500 to 3050
Fluorescent Lamps:
Warm White: 3000
Cool White: 4100
Daylight: 6500
Sunlight at noon: 5500
Overcast Sky: 7000
Clear Blue Sky: 10,000 to 30,000”
Nanometer: One billionth of a meter.
Alternate Definition: A measurement of wavelength. (this relates to color) All light is made up of electromagnetic waves. These waves act just like waves in the ocean. Or better yet sound waves. Different lengths produce different things. For sound it equates to pitch, for electromagnetic waves it relates to the type of wave (i.e. radio wave, x-ray, gamma ray, visible light). Visible light falls between roughly 400nm and 700nm. Above 750 or so is infrared, below 400 is UV. Nanometers refer to color within the 400-750. This is how nm can be applied to the aquarium industry. Often lights will show a spectrum analysis on the packaging showing various spikes at different nm.
Watt: “a unit of power equal to the work done at the rate of one joule per second” (Webster’s)
Alternate Definition: The amount of energy used to run a light. Contrary to popular belief this does not dictate the output of light in lumens. For instance a standard output 40 watt fluorescent puts out between 2,000 and 3,000 lumens (Natural Reef Aquariums), whereas a 175 watt Metal Halide puts out 15,000 lumens (Natural Reef Aquariums). If you do the math, 175watts of NO Fluorescent light equates to 8,750 to 13,125 lumens. Even the best Normal output fluorescent cannot create as much light as a metal halide of equal wattage.
Ballast: A device used to supply enough energy to “fire” fluorescent lamps and high intensity lamps. Once the lamp has fired the ballast supplies the correct energy to the lamp. Ballasts are not interchangeable between lamp types and often between wattages. Discuss this with who you buy it from.
Electronic ballast: Same as above but it uses electronics to run cooler and with less energy. These ballasts can often run multiple wattages (check with your retailer). They also maintain the spectrum of the lamp longer as well as the life of the lamp. The catch is they are twice as expensive (but well worth it)
The second step is figuring out what type of light you want:
This choice can be affected by the fauna you wish to keep along with your budget. There are many types of lights to choose from. These include but are not limited to: Fluorescent (Normal Output, High Output, Very High Output, Power Compacts), Metal Halide, High Pressure Sodium, Mercury Vapor and others. The two most available are fluorescent and MH. This should not limit you to the others, it just means there is less info out there to help you.
Normal Output: Come in sizes ranging from 18” (there are smaller ones too) on up (in one foot increments from 24&#8221 ;) Common sizes:
18”: 15 watt
24”: 20 watt
36”: 30 watt
48”: 40 watt
and so on
Advantages: Cheap, readily available lamps and ballasts, easy to work with, relatively cool. 03 Actinic lights can “fluoresce” certain colors of coral. Slim profile.
Disadvantages: Short spectral life, low output, large for the wattage produced. They only get bigger if you want more light.
Colors Available: Basically anything. The lamps lighting your house are in the high 3000°K to low 4000°K range. The scale moves on up to extremely blue colors (03 Actinic, 20,000°K lamps).
High Output: Come in sizes ranging from 18” (25 watt) – 120” (135 watt). Approximately 40% more light output than an equal length NO fluorescent lamp (
Advantages: Still relatively cheap. Slim profile. More wattage for the size.
Disadvantages: They run hotter than NO fluorescent lamps. Again more light means a bigger lamp. The ballasts are not as easy to find as NO, VHO, or PC. Not every LFS will have the lamps in stock.
Colors Available: Daylight, 50/50, and 03 Actinic are the most common for the aquarium trade.
Very High Output: Come in sizes ranging from 48” to 96” ( They produce 50% more light than that of a NO fluorescent lamp of the same length.
Advantages: More wattage for the size. Easier to get than HO lamps. Slim Profile.
Disadvantages: Not as cheap (although relatively speaking still pretty cheap). These run hotter than NOs by quite a bit. Parts are harder to find than NOs.
Colors Available: Again: Daylight, 50/50, and 03 Actinic are the most common for the aquarium trade.
Power Compacts: Come in sizes ranging from 9 watt mini bulbs not more than 8” long to much larger bulbs. The three most common bulb sizes are:
12.6875” 28 watt
22.6875” 55 watt
33.6875” 96 watt
Advantages: A lot of light for the size. Slim profile.
Disadvantages: Expensive. Parts are not as available as NO. They run hot. Some people complain that PC actinic’s are not as “true” as NO, HO, and VHO. They still don’t produce as many lumens per watt as metal halide and other high intensity lights. The following is information pulled from a lighting supplier (if someone needs the name, for legal purposes, e mail me, but I figure it may be against rules to post competing web page URL’s):
28 watt: 6700K: 1970 lumens
55 watt: 6700K: 4230 lumens
96 watt: 7600K: 8100 lumens
Again the math shows 12312.5, 13459.1, and 14765.625 lumens for the 28 watt, 55 watt, and 96 watt lamps respectively per 175 watts. Only the 96 watt is getting into high output range (certainly better than NOs).
Metal Halide: Metal Halide bulbs look more like conventional incandescent bulbs than fluorescent tubes. There are many advantages to Metal halide lighting... but with those advantages comes many disadvantages.
Standard sizes include: 175 watt, 250 watt, 400 watt, and even 1000 watt. The overall size of the lamp does not change between these sizes, just the size of the “packet” of halide gas inside the lamp.
Advantages: Small. High output. A 175 watt MH produces, as I said earlier, 15,000 lumens. The higher wattages produce even more per watt! There are extreme wattages available. How else can you fit 1000 watts of light over a 1’ cube ;) ?
Disadvantages: They are HOT!! These lamps run hotter than most other bulbs. They need at least 10” of hood space... preferably 12”. I realize people will come back and say that they kept there tank for years with the bulb ½” off the surface... but it does not mean it is a good idea. These bulbs need UV protection. Most, designed for the aquarium trade, come with a coating to limit UV rays. Those that don’t, need a supplemental shield. These bulbs need to be protected from spray. They are HOT... hot glass and cold water makes for neat explosions! This can happen. Again people will argue the point, but if you want to be sure to come home to your intact MH lamp and house protect them. They need cooling fans. The main point is they are hot :)
Colors Available: Basically everything. Nothing below 5500K is suitable for the reef. The most common are:
These colors are readily available from any place that sells reef lighting. All are suitable for reef lighting.
Other Options: There are other types of light out there. Most have not been explored in much depth. This, however, does not rule them out. The most important things to worry about are:
-UV exposure (true of High Intensity lamps [i.e. Mercury Vapor and high pressure sodium])
-Ballast needs
If these requirements are met, any of these lamps would work as well if not better.
You also need to worry about the Spectrum of the lamps you want.
There are some basic ground rules here. You need a bulb that will provide at least 5500K in color. Anything less will grow algae but not much in the coral department. Some colors are more pleasing to the eye than others. The bluer (higher K) the lamp, the better it looks to a point (of coarse this is subjective). I personally like 10,000K with or with out actinic supplement. Talk to other hobbyists, look at tanks at your LFS, ask them what type of lights they are running (assuming you like the color).
It should be noted that corals have their own needs. Corals from deep water are going to appreciate more blue light than daylight colors. Whereas an Acropora that comes out at low tide is going to thrive under daylight much better than blue light.
Remember also that spectrums shift. As a bulb ages it looses K temperature. So a 5500K lamp won’t remain suitable for as long as a 10000K lamp. These lamps also loose intensity... All the lights discussed should be replaced at least every year. If not sooner. Stagger the replacement process so as to not shock inhabitants.
When picking bulbs look on the packaging for a spectral analysis chart. A bulb gets a color temperature rating based on the average of the wavelengths in the output. This is important when looking at bulbs: Two daylight bulbs (both 6500K) could have very different spectrums. One could have an even range, while the other could have spikes in two or three places that average to the same 6500K. It is better to get a bulb that does not have spikes in certain wavelengths (other than the wavelengths you are buying the bulbs for...i.e. an Actinic having a spike in the blue wave length.)
How Much Light?
This is a question asked everyday. It is hard to say. I feel the Watts per gallon rule is silly. If for no better reason than different bulb type produce different lumens per watt. More importantly is small tanks screw it up. A 10 gallon still needs light. One should consider the depth of the tank, who will be living in it, and how they can control temperature spikes. The latter really should not effect your decision one bit, temp spike need to be taken care of rather than avoided (if it means you are compromising your lighting set up). The deeper the tank the more light is necessary. The higher the light needs of the animals the more light needed. There are some creatures that can live in low light (mushrooms, polyps) these should be the only inhabitants if you cannot afford a better setup. Save the money that would be wasted on higher light stock for the new lighting. There is nothing wrong with adding one or two bulbs at a time. In fact it is easier on your current inhabitants.
Hopefully this information all makes some sense... and helps you in your reefing.
Sprung, Julian Delbeek, J. Charles: Reef Aquarium Volume 1: 1994; Ricordea Publishing.
Tullock, John H.: Natural Reef Aquariums: 1997; Microcosm Press.
Webster’s New Encyclopedic Dictionary: 1993; Merriam-Webster Inc.