Light changes colour due to differences in its wavelength. Visible light, which is the only part of the electromagnetic spectrum we can see, consists of waves. These waves have different lengths, and these differences dictate the colour we perceive.
The Visible Light Spectrum
The human eye is sensitive to a specific range of electromagnetic waves, known as the visible light spectrum. This spectrum stretches from approximately 400 nanometers (nm) to 700 nm. According to the reference provided, these wavelengths are associated with different colours:
- Red: Longest wavelengths, around 700 nm.
- Violet: Shortest wavelengths, around 400 nm.
- In Between: The colours of the rainbow - orange, yellow, green, blue, and indigo - fall between these extremes.
How Wavelength Affects Colour
The colour we see is a direct result of the wavelength of the light that reaches our eyes.
- If light with a wavelength around 700 nm enters our eyes, we perceive it as red.
- Conversely, light with a wavelength around 400 nm appears violet.
- The other colours are perceived at corresponding wavelengths across the spectrum.
Essentially, if the wavelength of light changes, the perceived colour will also change.
Practical Examples
- Rainbows: When sunlight passes through raindrops, the different wavelengths of light are refracted at slightly different angles, separating them into the colours of the rainbow. This displays the entire visible spectrum.
- Prisms: Similar to raindrops, prisms can refract light, separating white light into its constituent colours based on their wavelengths.
- Traffic Lights: A red traffic light emits light with a long wavelength (around 700 nm), while a green traffic light emits light with a shorter wavelength.
Summary
The perceived colour of light is entirely dependent on its wavelength. The visible light spectrum encompasses wavelengths from approximately 400 nm (violet) to 700 nm (red), and these wavelengths determine what colour we see. Changes in wavelength directly translate to a change in colour.
