Lambert's Cosine Law

Diffuse Reflection

Diffuse reflection can be defined as the type of reflection of light or an incident ray where scattering happens at many angles and not just at one angle. Lambertian reflectance is the property exhibited by diffusely reflecting surface.

Lambertian reflectance is defined as that property of substances due to which they appear equally bright when from any angle.

This is the main difference between specular reflection and diffuse reflection.
Read more: Difference between specular reflection and diffuse reflection

Examples of Diffuse Reflection

• Paints: The matte paints that are used in home painting exhibit diffuse reflection while the glossy paints reflect diffusely along with specular reflection.
• Frosted glass bulb
• Human eye: The primary mechanism of the human eye is to reflect the incident ray in angles which is based on diffuse reflection.

Luminous Flux Derivation

Luminous flux is also known as luminous power which is the measure of the power of light perceived.

Luminous flux derivation is as follows

\(\begin{array}{l}F_{tot}=\int_{0}^{\frac{\pi }{2}}\int_{0}^{2\pi }cos(\Theta )I_{max}sin(\Theta )d\phi d\Theta\end{array} \)

\(\begin{array}{l}=2\pi *I_{max}\int_{0}^{\frac{\pi }{2}}coa(\Theta )sin(\Theta )d\Theta\end{array} \)

\(\begin{array}{l}=2\pi *I_{max}\int_{0}^{\frac{\pi }{2}}\frac{sin(2\Theta )}{2}d\Theta\end{array} \)

\(\begin{array}{l}=\pi sr*I_{max}\end{array} \)

Where,

sinӨ: Jacobian matrix determinant

I_max: luminous flux

To know more on reflection of light, refraction of light and their types, stay tuned with BYJU’S.

Related Physics articles:

Laws Of Reflection	Mirrors And Reflection
Reflection Of Light and Laws Of Reflection	Angle of Incidence

 
See the video below, to understand the law of reflection.

Frequently Asked Questions – FAQs

Q1

State Lambert’s cosine law

Lambert’s cosine law states that the radiant intensity from the ideal diffusely reflecting surface and cosine of the angle θ between the direction of incident light and surface normal are directly proportional.

Q2

What is Lambert’s cosine law also known as?

Lambert’s cosine law is also known as Lambert’s emission law or cosine emission law.

Q3

Define Lambertian reflectance.

Lambertian reflectance is defined as that property of substances due to which they appear equally bright when from any angle.

Q4

State true or false: The frosted glass bulb undergoes diffuse reflection.

True.

Q5

What is luminous flux?

Luminous flux is also known as luminous power which is the measure of the power of light perceived.