Light spectrum is measured by the Kelvin scale. Natural sunlight on a clear day registers at 5500 Kelvin degrees. Kelvin temperatures less than 5500 become more red and yellow and the higher the Kelvin temperature the more blue the light is. Photosynthetic invertebrates should be kept under lamps rated at or near the Kelvin temperature where the invertebrate was collected. Shallow water species should be kept under 10000K lamps while deep water species would prefer 20000K lighting. Longer photoperiods can not compensate for incorrect light spectrum or intensity.

Actinic lighting peaks in the 420 nanometer range and emits a fluorescent blue light and is usually used as supplemental lighting. Not only is actinic lighting beneficial to photosynthetic invertebrates, it is also aesthetically pleasing to the eye when used to supplement "daylight" lighting.

Freshwater aquarium plants benefit from lighting with a Kelvin temperature in the range of 5500 - 6500 degrees. Freshwater plants prefer light with more red and yellow in the spectrum.

All aquarium lighting should be on a timer to regulate the light schedule. The life cycle of your fish and corals revolve around your lighting schedule. The photoperiod of your aquarium should not exceed 12 - 14 hours of light per day.

For most aquarists, a simple, inexpensive 15 amp timer found at any hardware store will suffice for controlling the length of the photoperiod. Aquarium light controllers on the other hand will replicate the natural sunrise and sunset of the day by slowly dimming the lights on in the morning and off in the evening.