This is the most common type of lighting sources we use. It is also one of the least efficient. This passes electricity through a metal filament to produce heat. When the temperature reaches 500 degrees C (943 degrees F) the filament begins to give off light as well as heat. The light generated is adequate to see with, but is quite different from the light of the sun. This is because most of the energy that an electric bulb uses is wasted in producing infrared radiation (heat), only about six per cent of the energy input is used to produce light. The resulting light is heavy on red color and its neighbors, but contain very few violet, blue and green.

Fluorescent Strip Lighting

This is very popular in offices and factories. This is more efficient. But the light emitted differs from that generated by the sun. Within the glass tube of a fluorescent lamp, ultra violet rays are generated by a mercury vapor arc. The tube is lined with specially designed luminescent compounds which, when hit by the ultra violet rays, emit light of certain colors. Which colors are emitted depends on the type of compounds used to line the tube. Generally these tubes are designed to give off a high level of yellow-green light, the colors to which the eye is most sensitive. Thus they offer a seemingly very bright light while using relatively little energy. However, like the incandescent bulbs, their light is significantly different from that of the sun.

Full Spectrum Lighting

A few lighting manufacturers have built indoor lights that approximates natural daylight in intensity and color spectrum. What they have done is to replicate the spectral balance of daylight. These lights emit a certain amount of ultraviolet as well as all colors in daylight from red to violet. These lights are called full spectrum lights and are very useful for light therapy for SAD.