The apparent intensity of the light will vary inversely with the distance from the observer to the source. Electromagnetic wave motion involves the propagation of energy from a source to a detector. The rate of energy transfer is expressed as intensity. Light sources emit electromagnetic waves in all directions. A lamp emits radiation when electric energy is supplied to the lamp. The illumination of a surface is perpendicular to the luminous intensity of a point light source and is inversely proportional to the square of the distance. Light travels radially outward in straight lines from a point source that is small compared with its surroundings. The experiment studies the light intensity from different types of light sources. These different light sources could be a fluorescent tube, incandescent bulb, halogen lamp, mercury lamp, light emitting diode, and laser diode.