There are approximately 25 lumens in each foot candle.

There are approximately 25 lumens in each foot candle.

• A. True
• B. False
• C. Depends on the lamp type
• D. Only for natural daylight

Answer: (B)

Illuminance is measured in foot-candles, and it’s defined as how many lumens are spread over a square foot. In other words, one foot-candle means one lumen distributed across one square foot. There isn’t a fixed number of lumens “in” a foot-candle; the total lumens you need depend on the area you’re lighting. So the statement is false. If you have 25 lumens spread over 1 square foot, you have 25 foot-candles. If you want a certain foot-candle level on a larger area, you multiply that level by the area to get the total lumens needed. For example, 25 fc on 4 square feet requires 100 lumens in total. Lamp type or daylight vs artificial doesn’t change this relationship—the unit definitions themselves stay the same.

Illuminance is measured in foot-candles, and it’s defined as how many lumens are spread over a square foot. In other words, one foot-candle means one lumen distributed across one square foot. There isn’t a fixed number of lumens “in” a foot-candle; the total lumens you need depend on the area you’re lighting.

So the statement is false. If you have 25 lumens spread over 1 square foot, you have 25 foot-candles. If you want a certain foot-candle level on a larger area, you multiply that level by the area to get the total lumens needed. For example, 25 fc on 4 square feet requires 100 lumens in total.

Lamp type or daylight vs artificial doesn’t change this relationship—the unit definitions themselves stay the same.