According to lambert's cosine law, the illumination at any point on a surface illuminated by a source of light, with light rays inclined at an angle θ to the normal at that point, varies as:

Correct option is B

​$$\text{Lambert’s Cosine Law states that the illumination } E \text{ at a point on a surface is directly proportional to the cosine of the angle } \theta \text{ between the direction of the incident light and the normal to the surface:} \\[8pt]E \propto \cos \theta \\[10pt]\bullet \ \text{When light falls normally } (\theta = 0^\circ), \text{ illumination is maximum.} \\[4pt]\bullet \ \text{As the angle of incidence increases, illumination decreases according to } \cos \theta .$$​​