Good lighting design provides a suitable "brightness pattern" for each room based on the recommended average footcandles of incident light on the floor of the room to be illuminated. The principal factors to be considered for satisfactory room lighting are the following.

• Room dimensions: ceiling height and floor area

• Architectural or structural features that can affect lighting

• Reflectance, diffusion, and absorption of light by ceilings, walls, floor, and furnishings

• Proper selection of luminaires by evaluating their light distribution, efficiency, decorative value, elimination of glare, and economy

• Height and spacing of luminaires within rooms based on room function

Luminaires, receptacles, and switches should be distributed among many branch circuits in homes or offices to provide alternative light sources if one branch is disabled by a short circuit or overvoltage. Enough light should be available from alternative sources in the same or adjacent rooms to permit the occupant or occupants to correct any obvious faults in the disabled branch circuit and still reach the loadcenter safely to restore power.

Lighting design includes the estimation of lighting loads as well as the power requirements of all major appliances and building services. Because of the variables in these estimates, the lighting loads should be slightly overestimated to provide excess capacity for safety reasons. As a rule of thumb, it is recommended that no branch circuit be loaded for more than 80 percent of its capacity. The total ampacity in...