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Re: Frustrating Flicker in Fluorescents (WAS: Season misconceptions innewspaper)



John Clement wrote:

Many fluorescents apparently now lack the actual fluorescent layer.
They emit extremely strong spectral lines, unlike older tubes which show
weaker lines. Teachers on a budget can use these to demonstrate
spectral lines rather than buying expensive gas tubes.

The fluorescent coatings are still very much there, but there has been a
change of strategy by the lamp manufacturers.

Every fluorescent lamp coating is a mixture of different phosphors, each
radiating in a specific band of frequencies. The old strategy was to
try to create a broad spectrum by using broad-band phosphors radiating
many different "colors", thus trying to somewhat duplicate a "normal"
spectrum (e.g., sunlight). Unfortunately, this strategy hasn't worked
as well as hoped and fluorescent lighting has become infamous for
off-color tones such as slightly ghoulish green and yellow casts.

The new strategy is to use fewer and brighter phosphors, perhaps as few
as 3 (e.g. red, green and blue). When one looks at the spectrum
produced by a tri-phosphor coating, one is tempted to predict a garish
and unpleasant outcome. But the actual result appears quite
attractively "white" to most people. It makes sense if you remember
that your TV and your computer monitor create "whiteness" using only 3
phosphors.

Good reading for those who want to get up to speed on the applied
physics of fluorescent spectra is the technical bulletin at
<http://www.sylvania.com/forum/pdfs/faq0041-0800.pdf>.

Also, you might want to read my Nov 2001 posting (he said shamelessly),
commenting on the Sylvania bulletin and on the subject of phosphor
mixing and layering, in the PhyShare list archive at
<http://lists.psu.edu/cgi-bin/wa?A2=ind0111&L=physhare&P=R6135>.

Best wishes,

Larry

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Larry Cartwright Retired Physics Teacher
<exit60@cablespeed.com> Charlotte MI 48813 USA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- Good judgment comes from experience,
and a lot of that comes from bad judgment.
- If you're leadin' the herd, take a look back
now and then to make sure it's still there.
- A good time to keep your mouth shut is when
you're in deep water.
- If you're lookin' for permanent employment,
scratch a dog.
- Learn from the mistakes of others. You ain't gonna live
long enough to make 'em all yourself.
-- from The Cowboys' Guide To Life
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~