(Fwd) Re: Color UV?

["Willem-Jan Markerink" <w.j.markerink@xxxxx>]

From: Nick Cuccia <cuccia@xxxxxxxxxxxxx>

On Fri, 24 Jan 1997 21:01:21 GMT  Zoe Paddy Johnson CIRT CSOS wrote:
>> In one of my old Biology text books there were two color pictures of some 
>> flowers.  One was regular color, the other was the same flowers with the 
>> uv markings showing up as blue.  It is long enough ago that I don't know 
>> if the blue in the original picture was dropped out.  It wasn't false 
>> color, because the green was still green.
>> 
>> Does anyone know how the second picture was made?

Zoe and Geoff, 

There's an option that I didn't see in your list.  Think about "black lights",
which emit radiation in the far violet and near-ultraviolet.  Certain pigments
and materials, when illuminated with this form of light, will *emit* light,
or *fluoresce*.

This occurs in nature in plants, animals, and rocks, and has been harnessed by
man in a number of ways--1970s-vintage "black light" posters, bluing in laundry
detergent (a "brightener", it really glows when hit by UV.  If you've seen
white tee-shirts or cotton clothing glow under black light, this is what causes
the effect), and fluorescent lamps (which radiate oodles of UV; the visible
light comes from the white coating on the tubes).

It's quite possible that the subject was irradiated with UV light, and the
fluorescence caused by the UV radiation was recorded with visible film.

--Nick

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