radiance

Other Definitions
radiance (dict)

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

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 \ \

where

s the	radiance (watt · m^-2 · sr^-1)
Phi;	is the	radiant flux (Watts)
theta;	is the	angle formed by surface normal and direction of radiance L (rad)
\|is the \|area (square metres)
math>\vec{\omega}	is the	solid angle (sr)

whereas

\Phi = \frac{dQ}{dt}

Q = \int_0^{\infty} Q_{\lambda} d\lambda

Q_{\lambda} = n_{\lambda}e_{\lambda} \,

e_{\lambda} = \frac{hc}{\lambda}

where

s the	energy of light (J)
\|is the \|time s
math>Q_{\lambda}	is the	energy of light at wavelength λ (J)
lambda;	is the	wavelength (m)
math>n_{\lambda}	is the	number of photons at wavelength λ
math>e_{\lambda}	is the	energy of a photon at wavelength λ (J)
\|is the \|Planck's constant (J · S)
\|is the \|speed of light (metre per second)

Radiance

Definition

SI radiometry units

See also