Like all waves, light carries energy. The section of the optics, which are considered energetic characteristics of light in its broadcasting, distribution and interaction with a substance called Photometry.
1. Flow of light energy - energy transmitted through a surface per unit time. For example, the pupil of the eye glass window. If a body absorbs light fell on it, its internal energy increases, and thus its temperature increases. By changing temperatrata judge the flow of light energy. The unit of luminous flux of energy is J / s - W.
2. Photometric magnitudes
a) flux - Ф
Ф = K(λ). Ф(E)
The work flow of light energy with a wavelength value and the spectral sensitivity of the eye for this length λ = 555 mm (green light). To produce the same sensation, the flow of red light with λ = 650 nm should be almost 10 times greater than the flow of green light. This means that the sensitivity of the eye to green light is 10 times greater than the sensitivity to red.
In light below 400 nm and above 780 nm sensitivity of the eye is 0.
The flow of light energy waves outside the visible area may be different than 0, but the light output of them is always 0.
b) luminance - E
E = F / S
The brightness of a surface prosht S is called luminous flux F that falls on a unit area of surface. The human eye can not determine with precision Are the brightness of two adjacent surfaces - visual comparison.
The brightness can be measured with high precision devices called luksmetri.
In light of the photosensitive layer EDN occurs between the electrodes that is proportional to the brightness (EDN ~ E).
c) the intensity of light - I
I = E / S.t J / s.m ⋄ W / m
I = ΔФ / ΔΩ ΔΩ-solid angle
ΔΩ = ΔS/R2 = sr / steradian
ΔΩ = 4P.R2/R2 = 4p sr (the whole solid angle)
The intensity is characteristic of the light sources. The intensity of the light source in a particular direction is called luminous flux emitted in this direction in the unit solid