# Light Rays: Definition, Types & Sources

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• 0:00 What are Light Rays?
• 1:15 Types of Light Rays
• 2:05 Creating Light Rays
• 2:40 Lesson Summary

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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

This lesson will explain what light rays are, the main types of light rays, and how they can be simulated using lasers or beams of light. A short quiz will follow.

## What Are Light Rays?

Visible light is the visible part of the electromagnetic spectrum. The electromagnetic spectrum also contains things we cannot see. On the red side of the spectrum, there are radio waves, microwaves, and infrared. On the blue side, there are ultraviolet waves, x-rays and gamma rays.

In physics (and optics), a light ray is an idealized model of light, which is drawn as a straight line. Light can more realistically be considered as a wave, with peaks and troughs. But, if you draw a line that goes at 90 degrees to those peaks and troughs, you get a ray pointing in the direction the energy is flowing.

Light rays allow us to draw clear diagrams showing the motion of light, including reflection (like bouncing off mirrors) and refraction (the bending of light when moving from one transparent material to another). This is called ray tracing.

Ray tracing is useful for modeling things like reflection, refraction, and shadows. However, certain effects, such as interference and diffraction, can only be understood by looking at light as a wave. This is because they involve peaks and troughs creating light areas and dark areas. Trying to show interference and diffraction is a limitation of using rays.

## Types of Light Rays

While there are numerous names for types of light rays, the most common ones are incident rays, reflected rays, and refracted rays. Incident rays are the rays that approach and hit a particular surface -- they are said to be 'incident' on the surface.

Reflected rays are what you get if the surface is in some way reflective, such as in the case of a mirror. The ray that bounces off the surface at an angle is known as the reflected ray.

Refracted rays are when the light goes through the surface, bending due to the change of material (or 'medium'). For example, if a ray of light travels from air into water, or into a block of glass, the light ray will bend as a result. This effect is called refraction, and the ray that bends as it moves through the material is called a refracted ray.

## Creating Light Rays

Light rays are really nothing more than a model - they are a way of explaining how light moves. Within the light from a desk lamp, there are an infinite number of light rays that you could draw to show how the light moves through the room.

But there is a way to create something that looks like a light ray. By either putting light through a slit, or using a laser beam, we can create something resembling a light ray and show the effects of reflection and refraction. These images are examples of reflection and refraction using these beams of light.

## Lesson Summary

The electromagnetic spectrum contains many types of waves, and visible light is just the kind of electromagnetic wave that we can see. Light rays are imaginary lines that represent the motion of waves of visible light. These light rays are drawn at 90 degrees to the peaks and troughs of the wave.

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