Radiance - Definition and Overview

Radiance is a physical quantity used in the sphere of radiometry to measure the intensity of a light beam, defined as power per unit solid angle per unit projected area. The SI unit of radiance is the watt per steradian per square metre (w · m^-2 · sr^-1)

Definition

<math>L = \frac{1}{\cos \theta} \cdot \frac{d^2 \Phi}{dA d\vec{\omega}} = \frac{hc}{\cos \theta}\int_0^{\infty} \left\{ \frac{d^3n_{\lambda}}{d\vec{\omega}dAdt}\right\} \frac{1}{\lambda}d\lambda \ \ <math>

where

whereas

<math>\Phi = \frac{dQ}{dt} <math>

<math>Q = \int_0^{\infty} Q_{\lambda} d\lambda <math>

<math>Q_{\lambda} = n_{\lambda}e_{\lambda} \,<math>

<math>e_{\lambda} = \frac{hc}{\lambda} <math>

where

SI radiometry units

See also