Answers & Angles: What is an Angle of Incidence?


Have you ever wondered how to make a rainbow? It has everything to do with light, angles, and optics.

Read this guide to find out what an angle of incidence is, and how to use it in optics. Soon, you’ll be making rainbows (or finding more serious optical solutions) like a pro.

Why Are Angles Useful in Optics?

It is important to know the angles that the beams of light enter and leave a translucent or transparent prism such as a lens, or reflect from a mirror. For example, this can help you to get an accurate magnification or a focused image from a camera, or to align a laser beam for industrial uses.

Since light travels at light speed in a vacuum, but at different speeds in different materials, the angle or direction of the light beam changes when it goes through a prism, such as a lens, prism or a drop of water.

You can check out this guide to angles and optics for other optical terminology and any optics solutions your business might need!

What is the Angle of Incidence?

The angle of incidence is the initial angle at which the light travels towards the surface of the lens or mirror you are measuring. You measure the angle between the light beam and the perpendicular line from the surface, also called the normal line or normal vector.

The angle of incidence will have the same value as the angle of reflection on a flat mirror or other surfaces that have a high enough reflectivity.

For example, if the angle of incidence for a beam of light is 30 degrees from the normal line, it will reflect off of the surface at 120 degrees from the surface. From the normal line (which is always 90 degrees, or a right angle), you add the value of the angle of incidence to get the angle of reflection.

How to Make a Rainbow

Rainbows form when the angle between the light source and the observer is from 40 to 42 degrees. As the light in a spherical prism (or raindrop) diverges, 42 degrees creates the red light wavelength, and 40 degrees creates the violet wavelength.

You can use any light source and a prism to create a rainbow in your own home! Experiment with the angle of incidence to see where the angles of the refraction of the diverging beams, in this case the rainbow, occurs.

Since refraction does not follow the same pattern as reflection, the angle of incidence varies based on what shape you are using for a prism. The natural prism of falling raindrops causes the large rainbows we see in the sky after a storm.

Angling Toward Perfection

Angles in light help us determine how the angle of incidence will reflect from a reflective surface, or how it will refract through a transparent or translucent surface. These angles allow us to create everything from cameras to high-tech lasers. Check out our other blog posts to learn more about how businesses use technology and science to succeed!