ABSTRACT
This chapter considers the effect that lighting can have on maintaining alertness at night. There are a number of aspects of lighting that influence its effect on the circadian rhythm including quantity, spectrum, timing and duration. Environmental improvements can be made through better heating and ventilation but the major avenue for action is through lighting. Light can have biological effects over and beyond illumination and these can be used to improve both performance and well being. Light quantity is measured in lux and is generally measured at the working plane but can also be measured in the plane of the eye. Daylight intensity is relatively uniform over the visible spectrum, however artificial sources generally vary. Depending on the timing of exposure, light can either advance or delay the phase of the circadian cycle. The effect of light in suppressing melatonin appears to be dependent, the longer the exposure to the light then the greater the effect.
