Aquarium Lighting Essentials
Fish hobbyists and retailers alike know how to properly light an aquarium, but do they know how lighting really works?
Remember the good old days of aquarium lighting? Of course you don’t, because they didn’t include lighting. I have a few old aquarium magazines from 1913 entitled The Aquarium that include many advertisements for aquarium products, none of which were lighting fixtures.
Back then, hobbyists placed their tanks in windows so they would receive plenty of natural light. If there were live plants, they needed that light to prosper. So what if the tank turned green? All you had to do was change the water and maybe lower the window shade. Segue to the modern world where fish tanks require lights, filters, heaters and conditioners to make the water non-toxic for fish. Hmmm, I suppose you could call this progress. At least, it gives retailers a lot more products to sell.
How much do you really know about light? Permit me to give you a short lesson. As far as aquarium lighting is concerned, the term PAR is important, primarily when lighting a reef tank. PAR stands for photosynthetically active radiation. It’s the total number of photons within the visible light spectrum that fall over a square meter in one second. Photons are the smallest unit of light. They have no mass, but they do have energy. I’m talking about Einstein’s famous formula: E=MC². The energy in a body is equal to its mass multiplied by the speed of light squared. This should mean that photons have no energy, but, we know they do have energy.
The key here is that light behaves as though it does have mass. We know this because light is subject to gravity. Think of a black hole, an object in space with so much mass it sucks everything into it, including light. Basically, Einstein has proven that energy and mass may be the same thing. At rest, light has no mass. But when light moves, it has mass. This is relativistic mass—the mass of an object when it is moving versus when it is at rest.
It's All Relative
Okay, so what does this have to do with aquarium lighting? Where PAR values come into play is in a mixed environment with hard corals, soft corals and, of course, fish. Questions arise: Are stony corals photosynthetic organisms? Are they capable of photosynthesis?
Think of every green plant you ever saw, think of all the algae that grows in your aquarium—algae you work hard to get rid of. Animals require oxygen to survive. They consume oxygen from the air and give off carbon dioxide. Plants do exactly the reverse. When a plant takes in carbon dioxide from either water or air, it combines the CO² with water to form a chemical compound known as glucose or, as we call it, sugar. This is the process known as photosynthesis. It’s the basic energy source for almost all organisms.
Inside the reef-building, stony corals, there are commensal algae that produce glucose. This glucose is used by the coral to survive and grow. Energy is supplied to stony coral in two ways—actively and passively. The thing about becoming dependent on someone else to feed you is if they stop feeding you, you might not be able to survive. In an aquarium, if the commensal algae does not receive the proper light, it can no longer produce glucose. It may die, and if that happens, the coral will also die.
The commensal algae is collectively known as Zooxanthellae. It is a single-celled dinoflagellate that lives in symbiosis with not only corals, but jellyfish, nudibranchs, etc. In nature and in the aquarium, coral bleaching may occur if the Zooxanthellae are unable to produce food for the coral. Typical reasons this may happen include cloudy water, water temperatures too high, poor water quality and under- or over-active water movement. In captivity, however, the key factor is usually the light source reaching the coral. It must have the proper strength and the necessary wave lengths of light. And so, we return to the concept of PAR values.
A serious reefer will need a PAR-meter. But PAR-meters measure all light, not specific types of light. Also, PAR readings are taken in air, not water. A PAR-meter with a quantum sensor should be chosen. There has been much research done to determine what PAR value different corals utilize. Even if your lighting system is producing plenty of light, if the PAR value is wrong for your corals, they will do very poorly. The wave lengths of light reaching the coral are critical for success. If you get that right, then you need to supply enough lighting power to meet your PAR requirements.
Every single reef setup is unique and the PAR values that a tank requires vary greatly. No single fixture or system is going to work for everyone. The depth of an aquarium is a very important consideration when it comes to choosing total PAR output, but without the ability to flex the wave lengths of light produced, it may be almost worthless. To put it another way, brighter is not always better.
Over years of experimentation, coral hobbyists have figured out a lot about specific types or species of corals. The most important factors, in general, are strength and length of lighting, strength and direction of water flow, water quality, compatibility and preferred depth.
Types of Lighting
I wish I could tell you that there is one type or brand of light fixture that works better than others, but that’s not the case. With the move from incandescent to fluorescent, things have changed a great deal. We now have evolved to LED lights. Before LED lights, however, there were lights that could grow stony corals. These still exist, even if they are dinosaurs. Even today, I have clients that prefer halides and metal halides over LED’s. Why is this? It’s because with halides in general, it’s as easy as putting corals in the right locations and setting the timer on the lights. The heat produced from halides must, of course, be evacuated from the tank environment.
With LED’s, it’s a bit more complicated. LED stands for light-emitting diode. When current flows through it, it emits light. What’s a diode? It’s a semiconductor with two terminals allowing the flow of current in one direction only. Electrons in the semiconductor recombine with electron holes and release energy in the form of photons, better known as light. This effect is known as electroluminescence. The color of the light is determined by the energy required for electrons to cross the band gap of the semiconductor.
It has taken years of painstaking research to produce LED’s that can be used in thousands of applications. Perhaps, the most fascinating of these has been in the aquatic hobby, particularly when it comes to reef tanks. Light sources for stony corals need to have specific levels of light output in specific colors. This was not achieved overnight and even now, it continues to be refined.
Companies that sell LED fixtures for the aquatic hobby are not making the LED’s themselves. They are buying LED’s, some of which have been customized to their specifications. Then, they are designing equipment to deliver these LED’s to the consumer. They come in a variety of sizes, shapes and costs. In general, they are merely strips of lights in a small structure I would characterize as a light bar.
Research in LED’s has reached a level of sophistication that ensures the successful growing of hard or stony corals in captivity. There is now sufficient diversity in colors of lights, wavelengths of lights and strength or brightness of lights. When a proper package of LED’s is assembled, it can grow coral, grow aquatic plants or simply provide illumination for the average household aquarium.
The Right Light
As a retailer, your job is to help your customers select a light source that is right for their needs. For a fish-only aquarium with no live plants, your job will be relatively simple. Fish don’t really require a great deal of light. Live plants, on the other hand, have been found to prefer a light source that produces a Kelvin rating from 6,500 to 7,000K. In addition to this, a tank with live plants will require a minimum number of lumens per gallon. A serious aquatic gardener will need a LUX-meter that measures the number of lumens per square meter. While a planted aquarium or aquatic garden is very different from a reef tank, the one thing they do have in common is a minimum and maximum light requirement that should be varied from one location to the next, within a tank.
If you want to recommend a light source strictly for a freshwater fish tank, a simple fluorescent bulb will be sufficient unless the aquarium is 18 inches or deeper. Then, you should use twin lights of maximum wattage so the substrate receives adequate light. In reality, that’s more for the viewer’s benefit than the fish’s. Likewise, a wide tank of 18 inches or more should use two bulbs so the background and foreground are equally illuminated.
At this point, I can see no benefit to recommending LED light bars over fluorescent fixtures for freshwater set-ups. At least with fluorescent you’ll still be able to sell replacement bulbs to your customers—no such luck with LED’s. So far, when individual LED bulbs go out, they cannot be replaced. Just that fact alone will discourage some people from buying them. The future of lighting for the aquarium is still evolving. Who knows what tomorrow may bring? Stay tuned and keep up with innovations in the field of lighting. PB
Edward C. Taylor has been in the pet industry for more than 40 years as a retailer, live fish importer and wholesaler, and fish-hatchery manager.