The cosine law describes the relationship between illuminance (E), luminous intensity (l), distance from the light source (d), and the angle of incidence (θ). Specifically, it states that illuminance (E) equals the luminous intensity (l) divided by the distance from the light source squared (d2), multiplied by the cosine of the angle of incidence (Cos θ).

1. Cosine Law

2. Cosine Law

3. Cosine Law E = the “illuminance” in lux l = the “luminous intensity” in candelas in the direction of the point d = the distance from the light source to the work plane Cos θ = the angle of incidence in degrees E = l d 2 = Cos (θ)