Ray Optics and Optical Instruments

Lambert’s Cosine Law

Johann Heinrich Lambert describes this law and it is available in optics. This law is also called cosine emission law or Lambert’s emission law. Lamberts cosine law states that the radiant intensity about the surface or radiator of the ideal diffusely reflecting mechanism is directly proportional to the cosine of angle \(\Theta\) between the direction of the surface plain and emitted light. The main use of this law is in radiometry and computer graphics.

lamberts cosine law

                                                                                 Lambert’s Cosine Law

What is Diffuse Reflection?

Diffuse reflection is an incident ray or the reflection of light’s which appears as it is scattering from many angles from the source. Now the Lambert reflection is nothing but the illustration retrieved by the diffuse reflection. In Lambertian reflection, it is illustrated as the presentation of the object such that it is luminous in such a way that all the angles of observations are equal. This is the main difference between diffuse reflection and specular reflection.

Materials like plaster powder, fibres or white polycrystalline material mainly reflect diffused light at great efficiency but many common materials can produce both diffuse and specular reflection. Frosted light bulbs make on the principle of diffuse reflection. Matte finish paints also exhibit diffuse reflection. The human eyes vision is also based on the diffuse reflection as they reflect the incident ray in different angles.

What is Regular Reflection?

When the surface is mirror smooth then the image obtained by reflection is vivid and sharp. This is a regular reflection. Regular reflection is also known as specular reflection. But if the surface is a little rough or bumpy then the chance of image formation is less. The nature of the image is mainly fuzzy. So if the image is fuzzy or blurry then the reflection is the diffuse reflection.

Diffuse Reflection Mechanism

So when the rays reflect from the rough surfaces it causes diffuse reflection. In everyday life, we encounter diffuse reflection if the rays reflect from rough surfaces. From a leaf surface, diffuse reflection can occur as the cell infrastructure causes little roughness on the leaf surface. We cannot visualize the clear image in the diffuse reflection because incident rays travel in a different direction but they don’t merge at all so we cannot visualize the clear image in diffuse reflection.

FAQs about Lambert’s Cosine Law

Q.1 Why can’t we visualize a clear image in the diffuse reflection?

Answer: We can’t visualize a clear image in diffuse reflection because the incident ray reflects in different directions but they don’t merge at all. So we cannot visualize the clear image in diffuse reflection.

Q.2: Give some example of illumination?

Answer: Bright porch light is the most common example of illumination. Illumination principles are also used in photometry and photometric bench.

Q.3: What is the difference between specular and diffuse reflection?

Answer: When the rays reflect from a smooth mirror-like surface and the image is sharp and vivid, it is a specular reflection.  But when the incident rays reflect from rough surfaces, the images are fuzzy and it is the diffuse reflection.

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