Light sources for rainbows

The best light source for a rainbow is a strong point source such as sunlight. Sunlight is ideal because it is so intense and contains all the wavelengths that make up the visible spectrum.

  • A human observer with binocular vision (two eyes) has a 1200 field of view from side to side. In clear conditions, the Sun can be considered to be a point-source filling just 0.50 of their horizontal field of view.
  • A wide range of visible wavelengths of light is needed to produce all the rainbow colours. The Sun produces a continuous range of wavelengths across the entire visible spectrum.
  • When atmospheric conditions like cloud or fog cause too much diffusion of sunlight before it strikes a curtain of rain, no bow is formed.
  • Artificial light sources such as LED’s, incandescent light bulbs, fluorescent lights and halogen lamps all make poor light sources because they emit too narrow a range of wavelengths and don’t emit sufficient energy.