
366 OPTICS FOR ENGINEERS
we know the intensity of a source, we divide it by the squared distance to the receiver
to obtain the irradiance on the receiver. These relationships are in Equation 12.4.
• The radiance of a source is the derivative of its radiant intensity with respect to projected
source area, A cos θ, according to Equation 12.6. The radiant intensity is the integral of
the radiance times the cosine of θ over the area of the source, as in Equation 12.7.
12.1.1.2 Radiant Intensity and Radiant Flux
If we integrate the radiance over both area and solid angle, we will obtain the total power
received from the source. There are two ways to accomplish ...