From: Tim/Joan Merrill (tmerrill@hotmail.com)
Date: Sat Dec 09 2000 - 10:43:43 PST
From: "Tim/Joan Merrill" <tmerrill@hotmail.com> Subject: Black light Date: Sat, 09 Dec 2000 18:43:43 -0000 Message-ID: <F1655LqN33HFnwpGR880000a797@hotmail.com>
Hi Andrea,
I teach physics in Concord. I may have some helpful information about
"black light". You'll probably get many responses, but here's my
contribution:
Black light does refer to UV, which is indeed invisible to humans, although
not to several other animals, such as some raptors ( a great story there)
and bees. However, the methods we usually employ to produce UV actually
produce a group of wavelengths, some of which are in the visible spectrum.
We see the visible wavelengths, usually violets because those are also short
wavelengths.
Fluorescence is a physical process in which the high energy of a short
wavelength (UV) is absorbed by an atom, some energy is changed to heat, and
then the remaining energy is re-emitted. A lower energy photon has a longer
wavelength (more towards the red) so we can see it.
The fluorescent paints in a 60's poster absorbed the short wavelengths and
then would re-emit variously colored longer wavelengths (depending on the
specific compounds in the paint). "White" objects, like clothing, also often
shine in "black light" because the washing detergents have fluorescent dyes
included to make the clothes look "whiter than white".
Regular fluorescent lights have a fluorescent powder on the inside of the
tube, which absorbs the UV it produces from the ionized gas inside the tube,
and reemits visible light for us to read by. The glass of the tube
prevents the majority of the UV from emerging from the tube. A "black
light" is often a "fluorescent" made of quartz ( which is more transparent
to UV, with no powder.
There's lots more, but this addresses your basic questions.
>Subject: black light
>From: "Andrea Laub" <alaub@latinschool.org>
>Date: Thu, 07 Dec 2000 18:12:07 -0600
>
>My 7th grade science class is studying light. A lot of the kids keep
>asking about black light. My understanding and limited research is that
>it is UV light - beyond the visible spectrum. Then how come we can see
>it? Why do flourescent colors and white glow? What is black light? I
>would appreciate some info., thanks, Andrea
>
>
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