6D INDOOR LIGHTING

In indoor illumination the light sources are enclosed by reflective surfaces that transform the space into a 'larger luminaire' that diversifies the nature of light arriving at any one visual task. While this makes the enclosed lighting loads difficult to quantify (such calculations can easily be off by 40 percent), the human eye can almost always compensate for such discrepancies with its wondrous flexibility, which often approaches 70 percent. For example, though the task plane lighting level for general office work is 75 fc, if one's computed level differs by 40 percent (meaning the actual lighting level may measure 45-105 fc) the 70 percent flexible eye can perform the task at any lighting level between 25-130 fc.

Following are brief lighting guides for various indoor environments.

Air, undesirable. Where air is humid, dusty, vaporous, or otherwise polluted, luminaires should be enclosed and gasketed.

Ceilings. High ceilings tend to be cast in deeper shade and thus have lower effective reflectances than lower ceilings of the same color. In such spaces the lighting should be stronger or fixtures should have pendent mounts. Attractive reflective ceilings may be revealed with ambient uplighting. For open ceilings with exposed structure, ducting, piping, and wiring, consider painting every surface flat back and installing no uplighting.

Cleaning. Many occupancies requiring low light (dining rooms, intimate restaurants, night clubs, garbage disposal areas, etc.) often require 60 fc floor-level illumination for articulate cleaning.

Control rooms. These spaces require diffuse dimmable ceiling illumination...