[11.1.5.2] In searchlighting: The point brilliance, E, from a distant light source depends on the inverse square law and the atmospheric transmittance according to:

E d^{2}=I (T_{1})^{d}  ,

where:

= the point brilliance

d = distance

I = intensity of the light source

T1 = atmospheric transmittance per unit distance, or transmissivity

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