Question

Which angle allows the soil to receive the most direct light from the lamp?

0 degrees
20 degrees
45 degrees
90 degrees

Answer 1

90°. When the lamp is directly overhead (rays hitting the soil perpendicularly) the light is most concentrated on a given area, so the soil receives the most direct illumination. (If angles were measured from the lamp’s beam to the surface normal instead, that perpendicular case would be 0°.)