Index Key:  PHY073
Author:     sirwin
Subject:    Visible light?
Text:       At what wavelength does visible light start?

Response #:  1 of 1
Author:      R.C. Winther
Text:        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.