Light in which the rays (emanating from a source) are parallel or as parallel as one can reasonably expect.
Non-semiconductor lasers can produce highly collimated light because the reflective mirrors inside the laser are pretty well exactly parallel. (semiconductor or diode lasers require collimating lenses) However, ordinary light from light bulbs etc can also be collimated through use of lenses. Direct sunlight - but not skylight or other light from the sun that has been reflected or scattered - is also fairly collimated since the sun is at a great distance from the Earth and so sunlight appears to be emanating from a relatively small area.
Truly collimated light does not follow the inverse square law.
cf. inverse square law, laser, refractive index, skylight.
Entry last updated 2002-04-24. Term 234 of 1487.
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