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Direct Digital Controls And Lab Practice Test

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What is a foot candle?
Correct Answer:
The amount of light produced by a lamp (lumens) divided by the area that is illuminated.
Explanation:
Foot-candle is a unit of illuminance, telling you how much light reaches a surface. It’s defined as lumens per unit area on that surface, specifically lumens per square foot. So if a lamp emits a total of 1000 lumens and those lumens land evenly on 100 square feet, the illuminance is 1000 divided by 100, which equals 10 foot-candles. That direct ratio—lumens divided by the illuminated area—is what foot-candles measure. The other ideas don’t fit as well: total lumens describes how much light a lamp emits overall (not how much lands on a surface), while lumens per square meter is lux (the metric version), and saying illuminance is measured in foot-candles is true but doesn’t express the calculation; D gives the exact relationship that defines the unit.

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