Editing Irradiance (section)

==Mathematical definitions==
[[File:photometry_radiometry_units.svg|thumb|upright=1.5|Comparison of photometric and radiometric quantities]]
===Irradiance===
Irradiance of a surface, denoted ''E''<sub>e</sub> ("e" for "energetic", to avoid confusion with [[photometry (optics)|photometric]] quantities), is defined as<ref name="ISO_9288-1989">{{cite web|url=https://www.iso.org/iso/home/store/catalogue_tc/catalogue_detail.htm?csnumber=16943|title=Thermal insulation — Heat transfer by radiation — Physical quantities and definitions|work=ISO 9288:1989|publisher=[[International Organization for Standardization|ISO]] catalogue|year=1989|access-date=2015-03-15}}</ref>
:<math>E_\mathrm{e} = \frac{\partial \Phi_\mathrm{e}}{\partial A},</math>
where
*∂ is the [[partial derivative]] symbol;
*Φ<sub>e</sub> is the radiant flux received;
*''A'' is the area.

The radiant flux ''emitted'' by a surface is called [[radiant exitance]].

===Spectral irradiance===
Spectral irradiance in frequency of a surface, denoted ''E''<sub>e,ν</sub>, is defined as<ref name="ISO_9288-1989" />
:<math>E_{\mathrm{e},\nu} = \frac{\partial E_\mathrm{e}}{\partial \nu},</math>
where ''ν'' is the frequency.

Spectral irradiance in wavelength of a surface, denoted ''E''<sub>e,λ</sub>, is defined as<ref name="ISO_9288-1989" />
:<math>E_{\mathrm{e},\lambda} = \frac{\partial E_\mathrm{e}}{\partial \lambda},</math>
where ''λ'' is the wavelength.