In addition, air conditioning consumes energy and may he required to remove the heat generated by lamps. To reduce it both input and hours of use must be controlled. Power input may be reduced by lowering general illumination levels, adopting selective lighting standards, and replacing inefficient sources. Hours of use can be reduced through sensible switching arrangements and automatic light control that takes advantage of available daylight and space occupancy. New Design Criteria Increased knowledge of the relation between visibility and illumination has led to new methods of lighting design.
Visibility is the new design tool.
Not only is it a most useful measure of lighting quality, but through visual performance studies it can also be used for specifying lighting levels in numerous working environments. The light-reflecting properties of an object and the direction of the incident light striking it have a greater effect on visibility than level of illuminance itself. Thus the traditional provision of a uniform illuminance level in the entire working space is being replaced by controlled illuminance concentrated at the work station. If work locations are uncertain or flexible within a space, then a general lighting scheme can be employed using luminaires with specific intensity distributions in computer-designed layouts. This can provide a uniform level of visibility but a non-uniform illuminance level across the interior space.