Nîret û Lûminans

Rêjeyên çemkirina qaraz di derêka tiştî de li ser her birîn cih bixweber per unit solid angle û per unit projected area bixweber derêka nîşan kirî ye li name radiance.
Radiance bi Le,λ din nehatiye û ewa tevahiyek dihêne ya double derivative ya radiant flux bi respect to projected surface area As û Solid angle ωs.

li ku, ÆŸ angle yek e di navnormal ê elemental û derêka tiştî de.
dAs elemental area yek e û dωs elemental solid angle yek e ku derêka tiştî yek binihêre.
Unit radiance W/sr-m2.

Li ser photometric quantity, radiance wek Luminance têne şandin.
Ew dikarin eqûlatiya conversion bikin bi luminance hatine jîn ji radiance.

Li ku, Km constant yek e ku wek maximum spectral luminous efficacy têne şandin û value ya wê 683 lm/W.

Luminance yek e luminous flux radiated ji point light source per unit solid angle û per unit projected area bixweber derêka nîşan kirî.
Luminance bi L

Unit Luminance Lm/sr-m2 an Cd/m2.
Ji hêla conservation of radiance û Luminance dikarin bin wereyên radiance luminance an luminance ji source û radiance û luminance ji detector yek binihêre i.e.

Çunki, ji hêla radiation niha neither gained nor lost in the medium in which propagation of energy takes place between the source û detector, then it must be that Φs = ΦD.
Luminance yek e quantity yek e ku conservation îne system.
Luminance yek binihêre ji source û at detector.
Luminance neither source quantity nor detector quantity.
Luminance purely geometric quantity yek e beam connecting the source û detector. Conservation of luminance also true for presence of lenses or other optics.

Basic relationship between the luminance û luminous flux given below,
Φ = LG,
G is geometric angle in steradian.

Brightness yek e Luminance

Luminance can’t be increased or decreased by any optical system. A system can only redirect the luminous flux. Suppose a page of a book has been considered with certain luminance. Then we can follow the equation below,

Here, ER is the Illuminance on the book that redirects to our retina. This equation means that our eye converts the luminance into Illuminance on the retina. All the other detectors do the same as what the retina does. The retina reacts to the flux density of the radiant field, that is to the Illuminance. The principle physiological sensation of brightness is linked to the luminance of the source we are looking at.
The radiance and luminance has a relation

Where, Km is the constant which is called maximum spectral luminous efficacy and its value is 683 lm/W.
Lv is luminance measured in cd/m2 and Le,λ is the radiance measured in W/m2-sr.

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