Choosing the right bulbs
To provide zooxanthellae with the proper wavelengths of light for photosynthesis, different bulbs have been developed to mimic sunlight filtered through different depths of water. As light penetrates water, different wavelengths with different "energies" will penetrate to varying depths. Red light (630-780 nm) penetrates to about 15 m, while blue light (420-490 nm) goes as deep as 250 m. So, it is not surprising that most zooxanthellae have evolved to absorb light best at 420 nm in the blue range. This has led to development of fluorescent bulbs that emit light primarily at this peak: Actinic 03-type bulbs. While you could use all actinic lighting on a reef, you may find the result disappointing. (Our eyes do not perceive blue light as very bright, and find yellow light more aesthetically pleasing.) Also recommended are "full spectrum" bulbs, "tuned" to produce light across the full spectrum, mimicking natural sunlight. These tubes show the true colors of corals and fish, and are pleasing to our eyes. Most reefs work best with a 1:1 ratio of actinic to full spectrum bulbs. Also available to hobbyists, are combination bulbs often called 50/50 or actinic white; these emit light across the full spectrum, with extra "actinic" phosphors for additional light at 420 nm. Most metal halides have adequate spectrums for reefs, though most hobbyists supplement with actinic 03-type bulbs to bring out corals' red and green fluorescence. Another effect of metal halide use, since they are a single point light source, is that we will get light defraction waves in the tank. While these waves are found in nature and are pleasant to the eye, they have not been shown to be essential to reef keeping.
The size and lighting choices that you make will have a big impact on the success of your reef. While this may appear confusing at first, make sure to take the time to research your options and then choose the ones that will allow your tank to thrive.
