Basic Electrical Engineering

Laws of illumination – Inverse square law, Lambert’s cosine law, Light, Electrical method of producing light

Laws of illumination

The illumination on a surface depends upon the luminous intensity, distance between the source and surface and the direction of rays of light.

It is governed by following laws.

1. Inverse square law

2. Lambert’s cosine law

Inverse square law

It states that the illumination of a surface is inversely proportional to the square of the distance of the surface from the source.

Lambert’s cosine law

This law states that the illumination on any surface is proportional to the cosine of angle between the directions of the incident flux and perpendicular to the area.


The radiant energy from a hot body which produces the visual sensation on human eye is called light.

Electrical method of producing light

Following are the methods of producing light:

1. Developing arc between two electrodes.

2. Passing a current through a filament.

3. Electric discharge through vapours or gases.

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