The filament which heats the mercury evaporates over time and the metal is
deposited on the nearest surfaces.  Many lamps have a cathode which
intercepts
the metal migration, but not all of it.  If you didn't require fast starting
lamps, no filament would be required in manufacture, but in this age no one
is
willing to wait 10 minutes for light after they throw the switch.

  *
  |  __O    Thomas C. Sefranek   tcs@cmcorp.com
  |_-\<,_   Amateur Radio Operator: WA1RHP
  (*)/ (*)  Bicycle mobile on 145.41, 448.625 MHz

http://hamradio.cmcorp.com/inventory/Inventory.html
http://www.harvardrepeater.org

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Ismail B - CTD, Chennai.
Sent: Friday, September 27, 2002 12:57 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: [EE] Fluorescent lamp darkening


Hello all,

Im just curious to know why fluorescent lamps (most of them) darken near
their filament ? What is the cause for that ? and Is it possible avoid it ?

...Ismail

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