Basic science

Light is the part of the electromagnetic spectrum that is visible to the human eye. It has wavelengths between 380 and 740 nm.

The electromagnetic spectrum is comprised of propagating waves produced by interactions between electric and magnetic fields. Electromagnetic waves are transverse, meaning that the vibrations forming the waves are perpendicular to the direction of travel. Similar to all waves, electromagnetic waves have a frequency, wavelength and speed. Frequency is the number of waves passing any given point per unit time. Wavelength is the distance over which the waveform repeats. The speed of light is therefore the product of multiplying the frequency of oscillation and wavelength.

Waves of the same frequency that reach maximal and minimal amplitude simultaneously are said to be in phase. In other words, their sinusoidal waveform graphs overlap perfectly.

Huygens’ theory of light describes the propagation of electromagnetic radiation as spherical waveforms, called wavefronts. Each point on a wavefront acts as a secondary emitter, producing its own spherical waveform. Because each point directly ahead of the old point is in phase, the waveform is recreated. Therefore, waves of electromagnetic radiation spread out in all directions in straight lines from the point source of emission.

A simple analogy is to think of a ripple produced in water when a stone is dropped. The circular ripple created by the stone represents a wavefront. If new stones were dropped at every point on the circular ripple, new ripples would form, and the waves would spread out radially in straight lines from the point of the original stone drop.

The speed of light in a vacuum is faster than the speed of light in glass, because light interacts with the electrons in the atoms of glass. When light crosses the boundary between two mediums, there is a change in speed, which alters the direction of travel. This is known as refraction. Larger drops in the speed of light as it crosses boundaries will result in a greater degree of refraction. The refractive index is the factor by which the speed of light is reduced when passing from a vacuum to any given medium.