Light spectrum
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Passing through a prism, light breaks down into six basic colors:
- The red, the orange, the yellow, the green, the blue and purple
- Indigo was traditionally added between blue and violet to achieve the magic number of seven colors.
Light is an electromagnetic radiation, made up of waves and particles:
- Photons are the particles carrying the energy of these waves
- Each wave has a frequency, a wavelength and an energy: the shorter the length of the wave, the greater its frequency and therefore its energy.
We can only see a part of these waves, those having a wavelength between 400nm(1) (violet) and 700nm(1) (red), which form the visible light:
- Below 400nm (smaller wavelengths), these are ultraviolet, then X-rays and finally high-energy gamma rays
- Above 700nm (longer wavelengths), these are infrared, then radio waves
When light changes medium (passing from air to water or glass, for example), it is deflected depending on its wavelength, the angle of entry and the nature of the medium. The greater this deviation, the better we can distinguish the different colors (or wavelengths) that make it up:
- A prism, because of its two non-parallel faces, allows a large angle of deviation: the Flint prism is a type of glass that further accentuates this dispersion
- Water droplets in the air offer the same phenomenon: it's the rainbow after the storm.
Some animals can see a wider or different part of the spectrum:
- Snakes distinguish infrared radiation
- Bees see ultraviolet but less well red
White is the sum of all visible colors, and black their absence.
(1) nm=nano meter: one billionth of a meter
