Lighting is Complicated

Lighting is complicated. People have won Noble prizes studying light and the effect it has on... everything. This little inquiry into light is by no means meant to be complete. It is a small snapshot of how light applies to the reef that I plan on building. This post will explain the importance of choosing the correct lighting for a salt water aquarium.

Light is energy; it is life sustaining. If someone desires to grow coral in their tank, which I do, then a light source capable of sustaining these light intensive animals is needed. There are, of course, many different types of coral. At the lowest levels of classification, corals generally fall into two categories: hard or soft. Hard corals come in two varieties, large polyped stony corals (LPS) and small polyped stony corals (SPS). Here are some examples. The picture on the top is of a soft coral, the middle picture is an LPS coral, and the picture on the bottom is of mixed SPS corals.




The best advice I can give to anyone interested in starting a salt water aquarium is to pre-plan what you want in your aquarium. For example, if you know that you want coral in your tank it will be cost affective to buy the right hardware in the beginning. It is difficult and expensive to incorporate corals into a tank that did not plan on having them in the beginning. I am designing a mixed coral tank. I want to incorporate corals that don't require a lot of light (soft corals), corals that require a lot of light (SPS corals), and everything in between. As a result I need a light strong enough to support the growth of the most light intensive corals, the SPS corals, but no so strong that it will burn everything. Yes, you can have too much light...theoretically. That is not for this discussion however.

Coral contain symbiotic, photosynthetic algae called zooxanthellae. First, a brief discussion of zooxanthellae. A basic description of zooxanthellae can be found on Algone.com. Next, photosynthesis. To avoid confusion, I will restate two facts I have already mentioned. Yes, corals are animals, and yes they harbour photosynthetic algae in their tissues. Very interesting indeed. Photosynthesis occurs in the visible light spectrum. As the diagram in the previous link shows, the visible spectrum of light is between 400 and 700 nanometers (nm). This is more important than it may appear. There are multiple colors (wavelengths) that contribute to the visible spectrum. Remember ROYGBIV: Red, Orange, Yellow, Green, Blue, Indigo, and Violet? These colors and their combinations give us the color that we see in life. Now, let's consider a plant. They are green for the most part, correct? That is because they absorb all colors except green. Because they reflect back green, they look green. But, they use the process of photosynthesis to derive energy from the light they absorb.

Corals don't look green, not all of them anyway. But they still use the process of photosynthesis to derive energy. Corals do more than just reflect and absorb light. The zooxanthellae are more diverse, and as a result, utilize light in different ways. Advanced Aquarist published a series of articles on corals and light. The articles, Fluorescence, Green Fluorescence, Yellow and Orange Coloration, Red Fluorescence, and Non-Fluorescent Chromoproteins touch on the importance of light spectrum and energy to corals. I suggest reading these articles to get an idea on the many different ways coral, zooxanthellae, and light interact. A quick summation of the articles is that through absorbance, fluorescence, and reflecting corals exhibit different colors under different wavelengths and energy levels of light.

So here is my point. The idea is to buy a light system that will allow the coral to display their most beautiful properties and allow them to thrive. Or, stated a little differently, the idea is to buy coral that can live in your tank based on the type of lighting you have. So how do you do this?

The best way to judge a light is by PAR ratings. In Facts of Light by Sanjay Joshi, PAR is defined as photosynthetically active radiation. PAR is measured in PPFD, or photosynthetic photon flux density, between 400 and 700nm in one square meter. Sanjay continues by stating that different bulbs have different spectral distributions. Even though two lights may have the same PPFD rating, the distribution of the wavelengths that contribute to that PAR rating (hint: that is the PPFD) probably differ.

Now is the time to introduce the hardware. There is fluorescent lighting, VHO fluorescent lighting, power compact lighting, T5 fluorescent lighting, and metal halide lighting. These are different types of bulbs that produce different amounts of energy at different wavelengths or color. In my next post I will talk about each briefly, and then explain why I choose the light that I choose.