### Lighting Theory: Radiometry and Photometry

Recent games have been heading towards Physically Based Rendering and this requires a solid understanding on lighting theory more than ever before. This time, I'm posting my note on

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*Radiometry*and*Photometry*.**Radiometry***is basically ideas + mathematical tools to describe light propagation + reflection.***Radiometry***Radiative Transfer*is a study of transfer of radiant energy (which operates on geometric optics level - macroscopic properties of light suffice to describe how light interacts with objects much larger than light's wavelength).*Four Radiometric Quantities*:*1.*

**Flux (Radiant Flux/Power)**- total amount of energy passing through a surface or region of space per unit time (J/s or Watt). Total emission from light sources is generally described in terms of flux.2.

*Irradiance (E)*- area density of flux arriving at a surface (Watt/m2)**- area density of flux leaving a surface (Watt/m2)***Radiant Exitance (M)*3.

*Radiant Intensity (I)*- flux density per solid angle (Watt/sr)4.

*Radiance…*

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