The amount of visible light projected onto a surface

The amount of visible light projected onto a surface

• A. Lux
• B. Candela
• C. Illuminance
• D. Lumen

Answer: (C)

Understanding how much light falls on a surface is illuminance. This quantity describes the amount of visible light that actually reaches and covers a given area, which is how bright the surface appears to the eye. Illuminance is measured in lux, a unit equal to one lumen per square meter. So illuminance tells you how many lumens are spread over each square meter of the surface (E = Φ/A, where Φ is luminous flux in lumens and A is area in square meters). In contrast, lumen refers to the total amount of light emitted by a source, regardless of how it spreads. Candela measures luminous intensity in a specific direction, not on a surface. Lux is simply the unit used for illuminance. Therefore, the quantity described as the amount of visible light projected onto a surface is illuminance.

Understanding how much light falls on a surface is illuminance. This quantity describes the amount of visible light that actually reaches and covers a given area, which is how bright the surface appears to the eye. Illuminance is measured in lux, a unit equal to one lumen per square meter. So illuminance tells you how many lumens are spread over each square meter of the surface (E = Φ/A, where Φ is luminous flux in lumens and A is area in square meters).

In contrast, lumen refers to the total amount of light emitted by a source, regardless of how it spreads. Candela measures luminous intensity in a specific direction, not on a surface. Lux is simply the unit used for illuminance. Therefore, the quantity described as the amount of visible light projected onto a surface is illuminance.