Light energy and intensity

Radiant energy spreads in all directions.


 * Radiant flux is the power transmitted by radiation, it corresponds to the radiant energy emitted by the source per unit of time.
 * Luminous flux expresses the intensity of the visual perception that is caused by the energy of light radiation passing through the space per unit of time (it depends on the wavelength of the light used).
 * Radiation intensity = radiant flux passing through the cross-section of the surface of the source (v m2).
 * Illumination = luminous flux landing on a unit area.


 * Radiance = the ratio of the luminous flux and the size of the solid angle into which this flux is emitted.
 * Luminance = luminous flux emitted by a point source in a unit solid angle.
 * Brightness = perpendicular luminance of the area divided by its size [cd/m2].


 * Luminous efficiency of radiation:
 * $$ K = \frac{\Phi}{\Phi_e} $$ [lm/W]
 * (Due to the different sensitivities of the eye to the different wavelengths, this quantity is a function of the wavelength.)


 * Lambert's law: the law expressing the decrease in luminance of a surface with increasing angle φ.
 * I&phi; = IN. cos &phi;, where IN is the luminosity in the perpendicular direction, I&phi; is the luminosity in the direction deviated from the norm by the angle &phi;. A light source satisfying this law is called a cosine emitter.

Related articles

 * Combined lighting, glare | Artificial lighting | Daylight