All Problems

Photometry and Geometrical Optics

Problem 5.5

A certain luminous surface obeys Lambert's law. Its luminance is equal to \(L .\) Find: (a) the luminous flux emitted by an element \(\Delta S\) of this surface into a cone whose axis is normal to the given element and whose aperture angle is equal to \(\theta\) (b) the luminosity of such a source.

Reveal Answer
 (a) Φ=πLΔSsin⁡2θ; (b) M=πL . \text { (a) } \Phi=\pi L \Delta S \sin ^{2} \theta ; \text { (b) } M=\pi L \text { . }
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