The interactive below uses an approximation of 1000 W/m^2 as the amount of energy from the Sun. Drag the slider to see how solar irradiance at the surface of the Earth is affected by the angle of the Sun.

Lambert’s Cosine Law is a major determinant of climate near the equator, the zenith angle (z) is always close to zero at solar noon. Moving closer to the poles, the zenith angle changes, which changes the amount of solar radiation that reaches the Earth’s surface.

The term “cosine response” is used to describe the behavior of a sensor that measures solar irradiance. A device with a good cosine response can estimate the direct irradiance by using the measurements at the surface and the zenith angle.