A luminaire is a complete lighting unit, comprised of a light source (lamp or lamps), together with the parts that distribute the light, position and protect the lamps, and connect the lamps to the power supply. The luminaire’s function is to direct light to appropriate locations, without causing glare or discomfort. With thousands of different luminaires made by hundreds of manufacturers, there are more luminaires on the market than any other type of lighting equipment. Choosing luminaires that efficiently provide appropriate luminance patterns for the application is an important part of energy efficient lighting design.Luminaires should be selected for optical performance (cut-off, distribution) and also for a high downward-light/output ratio (within the limits imposed by control of glare). Durable reflector materials having low rates of deterioration in reflecting power should be selected. For discharge-lamp luminaires in high-bay applications, glass refractor-reflectors have much to recommend them. Fluorescent luminaires should be selected from types having reflector surfaces and prismatic enclosures which do not tend to turn yellow with time. Bare-tube batten fluorescent-tube luminaires are inherently inefficient in use; although they have a high light/output ratio, they do not make the best use of the light.