Percentage Energy Due To Incidence Angle

This equation computes the percentage energy at a plane surface of light striking at an incidence angle (`theta`).  The incidence angle is defined to be 90 degrees when the energy is directed straight into the plane of the surface or the surface is pointed directly at the energy source.

The percentage of absorbed energy at the surface for a number of radiating energy phenomena varies by the sine of the incidence angle as illustrated in the graphic: