Wave-Particle Duality

Light is complicated as it can act as both a wave and as a particle.

A particle of light is known as a photon. These can be thought of as little packets of light, carrying energy. When we take a photograph on a modern camera, or on a telescope camera, we count these photons. The more we count the brighter an object is - we call this measurement the flux.

When light acts as a wave, it still carries energy, but it has a bunch of other information too. This helps us to understand more about it.

Every wave (e.g., light, water, or sound) has the following features:

Definition of wavelength and amplitude
Credit: Kraaiennest

Wavelength, λ: The length of 1 whole wave (crest to crest, or trough to trough).

Amplitude, A: The height of the wave. This is measured against the midpoint, or half the distance from the lowest point (trough) to the highest (crest).

Frequency, f: This is the number of waves which can be seen each second.

When we talk about visible light we mean the light we see with our eyes. It has a tiny range of wavelengths only about 400-700 nm or nanometres.  1 nanometre is a billionth of a metre - a human hair is about 100,000 nanometers! The wavelength of this light decides what colour we see with the longest wavelengths being red (~700 nm), and the shortest being blue (~400 nm). In between these are every other colour of the rainbow.