Calculations for Interior General Lighting

Lighting Codes

• What's referred to as 'adequate interior lighting' is a matter of individual preference. A dark room to one person may be well-lit to another. Ceiling lamps are preferred by some, while others like eye-level lighting provided by a table lamp. For this reason, the codes that determine the requirements for home lighting are flexible. A primary code, however, is that there must be at least one light in each habitable room and bathroom that must be controllable by a wall switch.

Mandated Switches

• In a kitchen and bathroom, the light switch must directly control a light, while in any other room, the switch can control a wall outlet that may or may not have a light fixture plugged into it. Homes with hallways, stairways, attached garages and detached garages need a wall switch control in each, according to the National Electric Code. Home entrances also need a wall-controlled switch operating a light outside the door.

Footcandles

• A common way to measure light is by using the unit of illuminance called footcandles, which is measured at the surface of the work area, not the light itself. The higher the foot candles, the more light is available to see with. The amount of footcandles desired for an individual dwelling room is left up to the owner, but the Illuminating Engineering Society of North America gives a specific recommendation of 30 footcandles for the kitchen stove, countertops, and other work areas.

Measuring Footcandles

• In general, 15 footcandles is the recommended lighting for home use. Areas with fine detail work such as sewing rooms and workbenches can go up to 200 to 500 footcandles. Not all lighting must be artificial, as windows and skylights also add to the available footcandles. Inexpensive light meters measure exactly what the available lighting is. Just place the meter on the work surface and within a moment, the meter will show the amount.