A beamwidth is the width or angle of a single beam of radiation.

In polar areas, solar radiation strikes Earth at a small angle. The dissipation of light in the Earth's atmosphere is increased when it falls at a shallow angle.

In polar areas, solar radiation strikes Earth at a small angle. The dissipation of light in the Earth's atmosphere is increased when it falls at a shallow angle.

The angle of incidence of a ray (or light or other electromagnetic radiation) to a surface is the angle between the incoming ray and the normal - which is perpendicular to the surface at the point of incidence

The angle of incidence is the angle between the incident ray of radiation (usually light) and the normal (perpendicular) at the point of incidence. Similarly, the angle of reflection is the angle between the reflected ray and the normal.