Radiance

Radiance is a radiometric measure of the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit of radiance is the watt per steradian per square metre (W·sr⁻¹·m⁻²).

Definition

Radiance, L, is defined by

L = d²Φ / dA cos θ dΩ

where

• d²Φ is the radiant flux (power) emitted,
• dA is the area that the flux passes through,
• dΩ is the solid angle that the flux is confined to,
• θ is the angle between the normal to the area dA and the direction of the flux.

Applications

Radiance has applications in many fields of science and engineering, including optics, photography, and astronomy. In practice, it is often used in the context of vision science to quantify the distribution of light arriving at a point on the retina of the eye.

See also

• Irradiance
• Luminance
• Radiant intensity
• Radiant exitance
• Spectral radiance

References

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