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glossary

Lambertian light source: light source with a constant radiance (or luminance) whichever the direction
Radiance ( radiometry ): for a light source or a diffusing/reflecting surface, power emitted per unit of solid angle and per unit of apparent area
Optical system: in geometrical optics, assembly of optical components for redirecting the light in a controlled manner
Refraction index: for a transparent medium, ratio between the light speed in the air and the light speed in the medium ; for a reflective surface in the air or vacuum, the refraction index is « - 1 »
Transmission: ratio between transmitted radiation power (or intensity or amplitude) and incident radiation power (or intensity or amplitude)