In a message dated 10/24/2003 1:18:43 AM Eastern Standard Time,
[log in to unmask] writes:

<< Ultraviolet energy (UV) is a component of visible light and part of the
electromagnetic spectrum. Wherever there is visible light there is also UV,
whether it is in direct line with the light source or "bounced". >>

David, just a quibble or two, although I'm no expert on electromagnetic
radiation.  I don't think it's accurate to say that ultraviolet is a "component" of
visible light.  Most light sources, including the sun, emit UV, infrared,
etc., along with "visible" light, but they're different wavelengths.  The
wavelengths of UV may *accompany* those of "visible" light from a given radiation
source, but one isn't part of the other--they're separate.  The wavelengths are
usually diagrammed as in a line along the electromagnetic spectrum, and I
wouldn't say they include each other.  And it may be misleading to say that
wherever there is visible light there's also UV, since wavelengths can, in theory at
least, be isolated from each other.  Filters transmit specific wavelengths
while blocking others.

Incidentally, my college optics professor always insisted that it's redundant
to say "visible" light, since light is by definition (originally) that
portion of the electromagnetic spectrum which is visible to the human eye--so the
term "visible light" is a bit like saying aqueous water, as if there were any
other kind.  He preferred to say that UV, infrared, light, etc., are forms of
radiation, not light.  Of course, dictionaries now often define "light" to
include visible light, UV, infrared, and even X-rays (although I seldom hear people
call X-rays a form of light).  This seems to be an example of semantic creep,
thanks to popular phrases such as "black light," etc.

David Haberstich

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