In this experiment principles of interference of light is used to determine the wavelength, of a light source. The interference fringe obtained here is a pattern of concentric circles, the diameter of which is measured using traveling microscope with micrometer.

If a clean convex lens is placed on a clean glass slide (optically flat) and viewed in monochromatic light, a series of rings may be seen around the point of contact between the lens and the slide. These rings are known as Newton's rings and they arise from the interference of light reflected from the glass surfaces at the air film between the lens and the slide.

In this apparatus, sodium vapor lamp and spectral LED’s are used as light source. LED’s of red, blue, green and yellow helps to plot the graph radius of the interference rings as a function of the order number for two wavelengths. LED is mounted on a post and post holder unit. Measurements are taken from a micrometer driven traveling microscope, which is made integrated with this apparatus