candlepower

Candlepower

Candlepower is a way of measuring how much light is produced by a lamp – a light bulb, or LED. It is a measure of light at the source (as equivalent to an ordinary wax candle) but not at the object you are lighting. And remember, a candle produces light in all directions.

Footcandles tell us how much of that light is directed at a specific object we want to illuminate when it is 12 inches (or 1 foot) away.

So another way of thinking about it is that candlepower is like “how loud I shout”, not whether you hear me or not.

On the NCIDQ Exam, all these terms: candlepower, footcandles, lumens, lux (and more) can be confusing, but would generally be used as relative measures of the output of one light source compared to another.