What is the Difference Between Luminance and Illuminance?

The difference between luminance and illuminance lies in the way they describe the characteristics of light. Here's a breakdown of the two terms:

• Illuminance:
• Refers to the quantity of light or luminous flux falling on a surface.
• Measured in lumens per square meter, or lux.
• Describes the intensity of light falling onto a surface area, like a wall or a desk.
• Luminance:
• Describes the amount of light emitted, passing through, or reflected from a surface.
• Measured in candelas per square meter (cd/m²).
• Reflects the intensity of emitted light or the amount of light reflected by the surface.

While both terms are related to light, they describe different aspects. Illuminance is about the amount of light falling on a surface, while luminance is about the intensity of light emitted or reflected from a surface. Luminance is often used interchangeably with the term brightness, but they are not the same. Luminance is a quantifiable, measurable characteristic, whereas brightness is a visual sensation perceived by the human eye.

Comparative Table: Luminance vs Illuminance

The difference between luminance and illuminance can be summarized in the following table:

In simpler terms, illuminance is the amount of light that falls onto a surface, while luminance is the amount of light reflected off the surface. Illuminance measures the incident light, and luminance measures the light leaving the surface.