Understanding Your Lighting System

This talk will hit the high points of more than two years' worth of research, and much of it is being presented for the first time here.

The various components of a lighting system are: The bulbs, the ballast, the luminator (reflector), the reflector material, and any shield under the bulbs.

The research was conducted using a Dawson Lux meter, a light quantum meter (measures PAR), and a UV meter with probes for UVA and UVB. PAR stands for Photosynthetically Active Radiation. It differs from Lux in that Lux measures light energy mostly in the range our eyes can see (primarily the green range), while PAR measures the entire 400-700 nanometer range, which includes the blue and red ranges most plants and zooxanthellae use for photosynthesis. PAR is just a better estimation of the light energy than Lux, sort of a glorified Lux reading. PAR is measured in microEinsteins (mE). As a reference, full sunlight is about 2000 mE.

How the research was conducted:

The sensors for the above meters were mounted on a two and a half inch square of plastic. A black box was built with a grid system set up, so that the sensor could be moved within each location in the box. The total area measured was a 2 foot by four foot area marked off in three inch grids. All the bulbs were nine and a half inches above the sensor. Any variations will be discussed in the case studies.

Case study 1: (4) 110 watt VHO fluorescents, no reflector. Maximum light reading approximately 1000mE at the top, dropping off in an oblong circle that stretches the full length of the 48 inch aquarium. Energy dropping off toward the sockets, most light made in center of tank.

Case study 2: (4) 96 watt Power Compacts. These claimed to make more light than the 110 watt VHO bulbs, and they did. (about 1100mE). These do not make most of their energy dead center, it's actually shifted off to the side somewhat. The lamp holder blocks virtually all light in the area beneath it.

Case study 3: 400 watt Horizontal mount Metal Halide: Note this phenomenon: The geometry of the metal halide bulb causes two areas of reduced light, one good-sized one out in front of the bulb, and one smaller one caused by the dimple in the end of the bulb. Not sure if this is caused by reflection or refraction within the bulb. Thus, if the bulb is mounted parallel to the long side of the aquarium, you will be casting a shadow in your tank. To do away with this phenomenon and maximize your lighting efficiency, the best design would be to have your bulbs perpendicular to the front of the aquarium. The shadow would then be cast out into your living room and not onto your corals. (You don't HAVE to do this to have a successful tank, it just optimizes the lighting system).

In this case, using a reflector, the PAR shows hot spots more intense than sunlight (2000mE). These very rapidly drop off, but even so, one 400 watt horizontal mount halide will give pretty good light distribution over the aquarium.

Case study 4: Pendant mount metal halide: (same bulb as used for horizontal test) : now there are peaks of 4000mE in a small area, double the intensity of sunlight. Then a fifteen inch circle that just about matches the intensity of sunlight. Thus, if you're going to use 400 watt pendants, you'll want two of them over a four foot long aquarium. You could sustain anything in this.

Please note that two bulbs of the same wattage will not necessarily make the same amount of light.

UV Radiation: measured in microwatts per square cm. per second. UVA is 320-400 nanometers, and UVB is 280-320 nm. UVA is not very good for your corals, but UVB is much worse.

Case study 5: Iwasaki 400 watt 6500K metal halide bulb, no reflector. UVA is half the level found in sunlight. That is a fair amount.

Case study 6: Power Compacts: These have UV peaks at the ends of the bulbs (not where they show the most Lux, interestingly enough). The daylight bulbs make the most UV, especially towards the ends. My readings are for UVB, they came out at 35 microwatts, which is not very high, but it does show that fluorescent bulbs do make UV.

Based on the studies done here, it does not appear that coral coloration is related to UV radiation. Thus, if you are using metal halide bulbs, and you're not shielding them in hopes that your corals will color up, you may actually be harming the corals with UV radiation.

Studies using reflector materials:

Used UVA radiation and four types of reflector: white, aluminum, mirrored, and none. There was no difference at all between the white reflector and no reflector. This was double checked several times because it was so surprising. The aluminum surface and the mirrored surface reflected UVA equally well. With UVB, each reflected differently, with aluminum reflecting the most UVB. In terms of PAR, the mirror came out as the best reflector by a small amount, the aluminum is a pretty good trade off, and then the white.

Studies using lenses:

Used four types of lenses: Lexan, Plexiglas UF4, mystery plastic, green glass. Results: green glass transmitted the most UV radiation. Lexan also transmitted a lot, and mystery plastic, where you don't know the makeup or origin, is certainly not good to use, it can transmit lots of radiation. Plastic lens material is recommended, and the Plexiglas UF4 transmitted the most PAR with the least amount of UVA and UVB. Coralife reportedly uses this in their fixtures.

Apparently some plastics degrade over time and begin to transmit increasing amounts of UV. This is an area I'm looking into now.

Changing Bulbs:

The first couple of weeks with an actinic bulb you lose 10-15% of your light. It then settles out and drops steadily but rapidly over six months. Thus, you should probably change these bulbs every five months or so. UV readings also seemed to drop off pretty proportionately.

Aquarium Light Brace study: This was a test of an aquarium that had a one inch dark plastic brace that reinforced the top of the aquarium. It absolutely killed the light in the center of the tank. But, DO NOT cut the brace out..if you've got one, you're stuck with it, it is holding the aquarium together! Same thing if you have a Plexiglas tank with an acrylic top on it…keep it clean or it will really cut down on your light transmission. Make it a regular part of maintenance.

Question: If you were starting a brand new large scale reef tank, what lighting system would you use?

Answer: For SPS corals I would use pendant mounted 400 watt bulbs every two feet. And I would shelter the animals from UV radiation with Plexiglas plastic.

Question: Do you get a dark spot from 400w metal halides when they are hung vertically?

Answer: Yes, you do. It is offset a bit, not directly beneath the bulb.

Question: Have you found any particular light levels in the tank needed to maintain coral coloration?

Answer: For purple coral it's about 5 or 6 hundred mE, I've seen reds color at around 250 mE. It seems that each color has a different threshold of light.

Question: Is there any way for a hobbyist to detect light falloff? Answer: every hobbyist should have a submersible lux meter and do immersion tests. I'm amazed that hobbyists have expensive pH and redox meters, but no light meters.

Question: You don't use the 10 or 20K's?

Answer: No, though I have. Based on what I've seen you'll do fine with 55 or 65.

I will be meeting with Dana Riddle in TN in about two weeks and will interview him some more on all of this and then update this page.

Albert>