From: SFPhysics@aol.com
Date: Fri Oct 22 1999 - 00:23:07 PDT
From: SFPhysics@aol.com Message-ID: <0.cf915e8c.25416adb@aol.com> Date: Fri, 22 Oct 1999 03:23:07 EDT Subject: Re: Pinhole Digest #267 - 10/21/99
> Hi everyone -- one of my students is doing a research project and would
> like to ask you a question. Here it is:
> What is Black Light and where can I find more info on the topic?
> What substances glow under Blacklight? Why?
> There you have it! Sarah Wise
> Sarah Wise
The term "black light" is the common form of saying Ultraviolet Light. UV is
just that, ultra means above and violet is the highest frequency with the
shortest wavelenght of light that we can see. UV is above the visible light
spectrum and below X-rays. Visible light that we see goes from about 7x10^3
to 4x10^3 Angstroms. UV goes from 2x10^3 Angstroms up to 1x10^1 Angstroms.
So the middle of the UV spectrum has a wavelength about 1x10^-8 metre. It is
a very wide part of the electromagnetic spectrum, hence you will hear of UVA
and UVB to denote longer and shorter wave lengths. Because UV is higher in
frequency than visible light it can have more energy. A flourescent
substance is one that takes the UV energy in in the form of an energetic
photon and puts out photons with energy lower in the spectrum where our eyes
are sensitive. The higher energy photon raises an electron up to a higher
level then when the electron sheds the extra energy by giving off a photon of
lower energy in the visible part of the spectrum we humans can see the object
"flouresce."
Flourescent substances are available from theatrical supply houses and even
local Long's, Walgreens, etc., around Halloween. Some monster makeup kits
are sold to be used by the children with flourescent makeup. The price of
"black lights" have come down to where they are now under $25 for a low power
unit.
Classic flourescent compounds are zinc sulfide, any one of a dozen laundry
soaps containing "brighteners" which use the UV induced glow to make "whiter
whites," some minerals such as Flourite, Calcite, Willernite, Wolframite,
Scheelite, and many phosphorus containing combinations. Whether they
flouresce or not is somewhat dependent on the part of the UV spectrum they
are exposed to.
For more information go to a good Internet Web browser and see what comes up.
Best of luck to you,
Al Sefl
Guaranteed to be correct 50% of the time!
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