Which unit measures illuminance on a surface?

Which unit measures illuminance on a surface?

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

Answer: (C)

Illuminance is the amount of light falling on a surface per unit area. The unit lux expresses this as lumens per square meter, so it directly measures how brightly a surface is illuminated. Lumen describes the total light emitted by a source, not how much lands on a specific surface. Candela is luminous intensity in a particular direction, not the amount arriving on a surface. Luminance describes the brightness of a surface as seen by the eye, usually in cd/m², and relates to how a surface appears rather than how much light hits it.

Illuminance is the amount of light falling on a surface per unit area. The unit lux expresses this as lumens per square meter, so it directly measures how brightly a surface is illuminated. Lumen describes the total light emitted by a source, not how much lands on a specific surface. Candela is luminous intensity in a particular direction, not the amount arriving on a surface. Luminance describes the brightness of a surface as seen by the eye, usually in cd/m², and relates to how a surface appears rather than how much light hits it.