Source: Gerstaecker · Auf Lager

<>

Understanding Luminance in Photometry

What is Luminance?

Luminance is a photometric quantity that describes the amount of light emitted or reflected from a surface per unit solid angle and unit source area. It is measured in candela per square meter (cd/m2 = lm sr−1 m−2).

Factors Affecting Luminance

The luminance of a light source is influenced by the luminous flux it emits, the size of the emitting area, and the solid angle into which it emits light. A light source with a small emitting area and emitting into a small solid angle can achieve high luminance.

For example, high-intensity discharge lamps and lasers with high beam quality can produce high luminance values due to their concentrated light emission.

Relation to Visual Brightness

For an observer, the luminance of a light source determines its visual brightness. If a light source could concentrate its emitted light into a smaller area while maintaining the same luminous flux, it would appear brighter to the observer due to increased luminance.

Luminance also affects the perceived brightness of a surface illuminated by a light source. As the observer moves away from the source, the apparent brightness may decrease despite constant luminance, especially at large observation distances.

Examples of Luminance Values

• The Moon: 2.5 × 103 cd/m2 (seen through the clear atmosphere)
• The Sun: 1.6 × 109 cd/m2
• Filament of a tungsten incandescent lamp: 107 cd/m2

Relation to Radiance

Luminance is related to radiance, a similar quantity in radiometry. Both are based on sophisticated concepts and share similarities in their definitions and applications.

Understanding luminance is crucial in various fields, including lighting design, display technologies, and vision science, as it directly impacts how we perceive light and brightness in our surroundings.

Source: Gerstaecker · Auf Lager
Feel free to comment your thoughts.