The Science Behind Rainbows

The Science Behind Rainbows: Optical Refraction and Dispersion

"As the appearance of the rainbow that is in the cloud in the day of rain, so was the appearance of the brightness round about.(Ezekiel.1:28)

Have you ever wondered what makes the colors of a rainbow? It is simply the effect of optical refraction and dispersion on white light as it passes through a prism. A prism contains two different mediums of different refractive indexes. This variation causes the light to bounce off of the prism at different angles and split into the component colors that make up white light, displaying a rainbow. A prism can be anything with two refractive indexes, even a droplet of water. This optical refraction and dispersion through water droplets is what causes the beautiful colors of a natural rainbow.

Optical refraction and dispersion: How a prism works

Dispersion and refraction of optics are responsible for the effect of a prism on white light. As normal white light passes through a prism, it will be converted into a rainbow of colors. The same processes of refraction and dispersion are also responsible for creating the beautiful colors of a natural rainbow. In the case of a rainbow, the droplets of water on the ground act as the prism, refracting the light twice and dispersing it into all of the colors of the rainbow.

Optical refraction and dispersion: Snell's law of refraction

As a beam of light goes from one type of medium to another, it is refracted at a different angle. The angle of this refraction is governed by Snell's Law, which states that the refractive angle depends on the refractive index of both of the media. The refractive index of a medium does not stay constant, but instead changes depending on the wavelength of the light passing through it. Light travels as an electromagnetic wave, with different wavelengths corresponding to a variety of rainbow colors. This makes it possible for the different colors to have a completely different refractive index even when passed through the same medium. The light is actually refracted twice, both when it travels into the prism and again when it is sent back out of the prism. This process of optical dispersion splits the white light into its individual rainbow colors.

Optical refraction and dispersion: Causing problems with camera lenses

While optical dispersion looks pretty, it can cause problems when it occurs with a camera lens. The lens of a camera or other optical device is basically just a curved prism, so it is subject to the same physical laws of refraction and dispersion that affect white light as it passes through a prism. This type of optical dispersion can happen with either type of lens, whether it is convex or concave. This usually requires the use of more than one lens in a piece of optical equipment such as a telescope or binoculars.