How Is Green Light Reflected, Absorbed & Passed Through a Red Glass Filter?

Light and Filters

• Different colors of light are defined by their wavelengths. For example, pure green light has a wavelength between 520 and 565 nanometers.

  You can use filters to separate light into colors. When you place a filter in front of white light, which is made up of all seven pure colors, the color that passes through will be the color of the filter. For example, if you pass white light through a red filter, red light will be transmitted and all other colors will be absorbed.

Reflection

• Objects only appear to be certain colors because they absorb all others. For example, a blue ball looks blue because it reflects the wavelengths that make up blue light and absorbs the other colors.

  A filter that lets red light through will also appear red because it reflects some of the red light too. If you shine green light through a red filter none of the green light will be reflected.

Absorption

• Absorption is the process by which all other colors are removed from the white light shining on an object in order to make that object look a certain color. In the example of a blue ball given above, all colors of light except blue are absorbed by the ball.

  A red filter absorbs all colors apart from red. Therefore, when green light is shined on a red filter, the green light is absorbed.

Transmission

• Filters are slightly different to opaque objects because they let some light pass through, in a process known as transmission.

  As well as reflecting red light, a red filter only allows red light to pass through. If you shine pure green light through a red filter, none of the light will be transmitted.