The lights we use for aquariums produce many different wavelengths of light, and the collection of these is referred to as the spectrum of light produced by that bulb. A 400 nanometer wave would appear very purple to our eyes, and a 700 nanometer wave would appear very red to us. A wide spectrum light is one that includes many different colors, and would appear to us as being white. A light focused on one area of the light spectrum, such as between 400 and 450 nanometers, would appear very bluish purple.

Bulbs suited for reefs tend to emulate the lighting conditions found on reefs in the wild. Since water is an efficient filter of longer wavelengths, blue is a predominant color under water. Reef bulbs are generally touted with color temperature numbers and spectrum graphs. Just remember that intensity is the primary focus; what the bulb looks like (i.e. the spectrum) is more aesthetic than anything.

Lighting intensity is by far the most important aspect concerning lights on aquaria. The intensity is most often what will determine the successful growth of photosynthetic plants (algae) and animals (i.e. corals). With these organisms, light is food and we need to feed them just as we would feed our fish.

Too often one will attempt to replace intensity with duration, but this is not a suitable substitute. Instead, increasing light duration can actually have a detrimental effect on plants and animals, such as increased stress (for animals that need “nighttime”), slower growth rates, and increased nuisance algae production.

In general, the higher intensity of lighting being utilized on an aquarium, the greater the diversity of life able to be maintained. The degree of intensity must be balanced with light duration and light spectrum based on the plant and animal mix for each ecosystem.