Diffuse illumination, coefficient of reflection, reflectivity and Lambert’s cosine Law

When an object is illuminated uniformly from all sides then it is known as diffuse illumination. Diffuse Illumination happens because light is reflected equally from the walls and ceilings and other objects. This reflection is diffuse reflection. Generally when light is illuminated to an object some part is absorbed by the object and some part is reflected back. Ratio of light reflected from surface of object to total light incoming to the object is known as the coefficient of reflection or reflectivity (R). Its value varies from 0 to 1. For white surface it is close to 1 and for black surface it is close to 0. The reason is that white surface reflects more light while black surface absorbs more light.

Lambert’s cosine Law: Reflection of light from an ideal diffusing surface varies as cosine of angle between the normal to the surface and the direction of the reflected ray.

Lambert’s cosine Law

If incident light from source is perpendicular to surface at a point, then that point is fully illuminated.

Iamb = ka. Ia

Where, Iamb = diffuse ambient

ka= ambient reflection coefficient,

Ia = Intensity of ambient light.

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