Editorial Feature

# An Introduction to the Models of Light

Light is an extraordinarily interesting phenomena. While it is known that light is a form of electromagnetic radiation, it is often convenient to model or describe light in a number of different ways, not just as a wave. For example, in spectroscopy and quantum mechanics, light is often described not as a wave, but as a particle. Some of these models include:

• The Ray Model
• The Wave Model
• The Particle Model

## The Ray Model of Light

The informal and intuitive way of showing light propagation is via the Ray Model. In the Ray Model, light is generally drawn or described using a system of direction indicated arrows. These merely indicate the path of the light. While this is simplistic, this is a very intuitive way of describing the phenomena that we are all familiar with, such as light reflecting from the surface of a mirror, or the way light beams shine through clouds.

The Ray Model is also very useful in the field of optics. Ray diagrams can be used to explain things like how lenses focus light, how the reflection of light works and how the direction of light is distorted by transparent materials of differing densities, such as glass or water. Figure 1. The cover of Pink Floyd’s album “Dark Side of The Moon” illustrates light being split into component colors through a prism. This is a pictorial representation of the Ray Model of light.

## The Wave Model of Light

The Wave Model describes how light propagates in the same way as we model ocean waves moving through the water. By thinking of light as an oscillating wave, we can account for properties of light such as its wavelength and frequency. By including wavelength information, the Wave Model can be used to explain colors.

The Wave Model goes beyond what can be described by the Ray Model alone. The Wave Model accounts for the performance and distortion of light when interacting with objects and openings that have sizes similar to the wavelength of the incident light. Although the Wave Model is applicable for the interaction of light with some relatively large objects, it is generally used when light is associated with objects under a micron in size.

## The Particle Model

The Particle Model for light is required to gain an understanding of how light interacts with atoms. Here, light is thought of as photons, tiny particles that contain energy related to the color, or frequency, of the light. The Particle Model is needed to explain how things like the photoelectric effect, why certain metals only emit electrons when absorbing light with a wavelength above a certain threshold, and lasers work. The Particle Model is at the heart of spectroscopy, which is all about the science of how light interacts with different forms of matter. 