Often standard fluorescent fixtures are utilized in areas where there may be existing computer areas containing VDT's or they may be areas that later are converted to computer areas with no attention paid to the type of lighting installed.

Computer areas must have lighting with minimum glare and cross reflection. Many ceiling fixtures are installed with parabolic reflectors to increase the downward light pattern and reduce stray light that may get to the ceiling and create glare and adverse reflections.

In many types of occupancies this is efficient light control but may be inefficient from a decorating point of view. The parabolic reflector gets the majority of the light downward but in doing so creates a phenomenon known as "dark ceiling". This effect may create a gloomy appearance in the room. You would not utilize this approach in a lobby or a cafeteria but you would want to use this in a computer area.

(See NRC publications #79, 44 and PK #117)

In an area where there is going to be a very intensive use of computers and especially in areas where the computers are installed in a very dense configuration, you would want to create the "dark ceiling" effect. This will reduce the amount of reflective glare transmitted to the computer screens.