View source for Radiometric and photometric quantities

==Photometric quantities==
Photometric quantities are limited only to '''radiation visible to the human eye''' . They are defined according to the [[spectral sensitivity of the human eye]] and are therefore dependent on the color composition of the investigated radiation (the human eye is most sensitive to yellow-green light with a wavelength of 555 nm). They are historically older than radiometric.

'''''Luminance''''' indicates the spatial density of light flux of the source in different directions. Luminosity can only be determined for a point source, i.e. for a source whose dimensions are negligible compared to the distance of the source from the control point. It expresses the ability of an approximately point source to induce visual perception in a given direction. Luminosity is a basic photometric quantity.

'''''Luminous flux''''' expresses the amount of light energy transmitted by radiation or emitted by a source per unit of time, taking into account the sensitivity of the average human eye to different wavelengths of light. It expresses the ability of a luminous flux to produce a visual sensation.

'''''Illumination''''' is determined by the proportion of the luminous flux and the content of the area on which this flux falls.

'''''The brightness''''' is determined by the ratio of the luminosity of the elementary surface of the source in the selected direction and the perpendicular projection of the surface in this direction.

'''''Illuminance''''' is the surface density of the amount of light that fell on a given surface in the time interval from t<sub>0</sub> = 0 to t – it is the product of the average illumination and the time t during which the illumination is active.

[[File:Solid_Angle.png|thumb| 600px | Grafical representation of a solid angle]] <math>
\Delta \Omega = \frac{\Delta S}{r^2}
</math>

<math>
I= \frac{\Delta \Phi}{\Delta \Omega}
</math>

<math>
E=\frac{\Delta \Phi}{\Delta S}
</math>

<math>
E=\frac{\Delta \Phi}{\Delta S}=\frac{\Delta \Phi}{\Delta \Omega \cdot r^2}=\frac{I}{r^2}
</math>
*<math>\Delta \Omega</math> = solid angle (sr),
*<math>\Delta S</math> = display surface,
*<math>r</math> = radius of light cone,
*<math>I</math> = luminosity,
*<math>\Delta \Phi</math> = luminous flux,
*<math>E</math> = lighting.