People often think of white noise as television static, or the serene sounds of rainfall and crashing ocean waves. But physicists and sound technicians use a much more specific definition.
White noise is random noise that has a flat spectral density — that is, the noise has the same amplitude, or intensity, throughout the audible frequency range (20 to 20,000 hertz). White noise is so named because it's analogous to white light, which is a mixture of all visible wavelengths of light.
Since it includes all audible frequencies, white noise is often used to mask other sounds. For example, some people use white noise machines as sleep aids to drown out annoying noises in the environment.
In fact, a 1990 study in the journal Archives of Disease in Childhood suggested that babies fall asleep quicker when under the influence of white noise. Additionally, white noise has long been used to help children and adults suffering from tinnitus (the perception of ringing, buzzing and other sounds in the ear when no external sound is present).
And given that it can cut through environmental or background sounds, white noise is often implemented into the sirens of emergency vehicles, helping people locate approaching ambulances, police cars and fire trucks easier.
Though you've no doubt heard about white noise before, you may be surprised to hear that a number of other noise colors exist, including pink noise, brown noise, blue noise and more.