The Qualities of Light
The main qualities of light that you need to know about when setting up and maintaining your aquariums are the color temperature, intensity, and wavelength. Each of these qualities should be considered, and what products you choose will depend on the types of marine animals you have.
The color temperature of light is expressed in degrees Kelvin, with a higher reading describing light that appears to be white and a lower reading corresponding to light that appears red or yellow in color. Light shining into water is filtered out by the water at varying rates, depending upon its color temperature. Red light is filtered out first, while green and blue light penetrate the water more deeply than do other colors. Modern lamp manufacturers take these factors into consideration in designing their products, so that your animals and plants can be shown to their greatest advantage.
Light intensity is measured in units called lumens. Light intensity is important to consider for viewing purposes and is critical to the survival of hard corals and certain other marine invertebrates. Plants also have specific light requirements and will only thrive if provided with light of suitable intensity. Light intensity is not, as is commonly believed, related to the wattage of the bulb in question. Wattage merely expresses the amount of electricity that is needed to turn the lamp on.
The wavelength of the light entering the aquarium is also of critical importance in maintaining plants, marine invertebrates and macroalgae. The effect of wavelength on the health of fish has not been well studied, but it is likely that future research will reveal it to be a consideration for many of these creatures.