Peter R. Boyce - Human factors in lighting
2nd edition
Lighting research center

Repeated exposure to UV radiation produces a protective response from the skin. Specially, with repeated exposure, pigment migration to the surface of the skin occurs and a new darker pigment is formed. Coincident with this, the outer layer of the skin thickens producing what used to be a socially accepted tan.
The effects of light on health can be conveniently arranged in four classes:
- the first is that light treated as radiation. For this class the definition of light is stretched to include UV and IR as well as visible radiation because many light sources produce all three types of radiation.
- the second is light operating through the visual system. Lighting conditions that cause visual discomfort are well known and easily avoided..
- the third is light operating through the circadian system. The wake-sleep cycle is one of the obvious circadian rhythms so it’s hardly surprising that exposure to bright light at the right time can be used to treat some sleep disorders involving the timing and duration of sleep.
- The fourth class is the use of UV radiation as a purifier of the air, liquids and granular materials. This role comes about because UV radiation has been shown to destroy many species of bacteria, molds, yeasts and viruses.

14.4.1
Lighting is a major user of energy.
Lighting is an attractive candidate for action to people who want to reduce electricity use, for several reasons:
First, the lighting industry has been diligent in producing more efficient light sources and luminaries.
Second, the controls industry has produced a number of device, such occupancy sensors, that can be used to control lighting so electricity is not wasted.
Third, lighting installations have a much shorter life, typically 10 to 20 years, than a building. This means that lighting will be replaced several times during the life time of a building, so the rate at which new lighting technology can be introduced throughout the building stock is faster for lighting than for other energy saving changes, such as improving insulation.
Fourth, lighting in buildings is usually accessible and can be changed with much less disruption than other proposed energy saving changes.