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Name: sirwin
Status: N/a
Age: N/A
Location: N/A
Country: N/A
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 arbitrary.

R.C. Winther

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