The lighting in a room produces comfort conditions when it achieves its objective of lighting the task adequately without being distracting and glaring or causing unnecessary visual fatigue. To produce comfort conditions the lighting must be designed to suit the requirements of our visual mechanism (the combination of eyes and brain). Light is that part of the electromagnetic spectrum which occurs between the infra-red and the ultra-violet. Adaptation is the process by which the eye adjusts itself to different luminances. Glare occurs when luminaires, windows or other sources, seen either directly or by reflection, are too bright compared with the general brightness of the interior. The IES glare index system enables the acceptability of discomfort glare to be assessed for proposed or existing lighting schemes. In certain cases visual acuity can be improved by viewing small detail in monochromatic light thus avoiding chromatic aberration in the eye.