[Beowulf] cold cathode fluorescent backlighting

Jim Lux James.P.Lux at jpl.nasa.gov
Fri Jun 29 14:27:03 EDT 2007


At 01:56 PM 6/28/2007, you wrote:
>On Thu, 28 Jun 2007, duane at duaneberry.net wrote:
>
>>  Even if a beta source inside a monitor/TV was continuously emitting the
>>physical  construction would provide more than enough shielding. For
>>power and regulatory considerations I doubt the source is on
>>continuously.
>>
>>  IMHO moving from CRT to LCD is a good move in general.
>
>Actually, TVs and monitors at one point in time were notorious sources
>of soft x-rays from where the electrons hit the glass.

Actually, another big source of Xrays was the HV rectifier tube.
Older tubes actually used to dimly fluoresce, but along there 
somewhere, they started using lead glass in the envelope.


>  Those of us who
>are old enough remember that we we were told not to sit too close
>because it could damage our eyes.  Those of us who sat too close anyway
>have a higher risk of cataracts and skin cancers.

are you sure that's not from playing out in the sun all summer in the 
days before SPF50 and solumbra fabric.


>Also, the beta source (generally a hot wire) IS kept hot at all times
>the CRT is "on",

The "instant on" feature actually doesn't keep the cathode at full 
temperature... typically it keeps it about half way there, so that 
when you turn it on, it only takes a second or two to come up to full 
temp/emission.  Keeping it at operating temp all the time would lead 
to reduced cathode/filament life from evaporation. Since the 
emission/evaporation rate is a very nonlinear function of 
temperature, running it just a bit cooler makes it last a lot longer 
(e.g. incandescent light bulb life goes as the twelfth power of 
applied voltage)


>On the biohazard side, the tubes inside an LCD contain mercury vapor,
>just like all of those compact fluorescent bulbs.

White LEDs?


Jim 


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