Date: Around 1993
At what wavelength does visible light start?
I looked in some of my physics texts, and there are disagreements
on exactly what is meant by "visible light". One book speaks of a "standard
observer"; another intentionally avoids description in terms of response of
the human eye. Both agree pretty much on the frequencies, however: from
about 3.84 x 10^14 Hertz to 7.69 x 10^14 Hertz. This corresponds to a
wavelength range from about 3900 Angstroms to about 7800 Angstroms. The lower
frequency (and larger wavelength) corresponds to the lower limit of red light,
and the higher frequency (and smaller wavelength) corresponds to the upper
limit of violet light. I would not be surprised if there is an "official"
international scientific definition of the various regions (microwave,
infrared, visible, etc.) of the electromagnetic spectrum, though I have not as
yet found mention of such; however, the divisions are, in any case, somewhat
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Update: June 2012