🚀 go-pugleaf

> >Also, in a less important way, the CRT is one of
> >very few electronic components that performs more poorly from constant use.
> 
> 	With one minor caveat to the above:
> 
> 	1/ Many good terminals, (such as the one I am using now,) have a
> 	   screen saver feature that blanks the screen after some time without
> 	   activity. This greatly improves the longevity of the phosphor.

Unfortunately, the phosphor is only part of the CRT aging problem; the other
part is the decrease in cathode emissivity with age, which is NOT affected
by the typical "screen saver".  Actually, the cathode life can actually
be degraded by the "blank screen" version of screen saver; yes, the tube is
cutoff, but the cathode is still maintained above its critical temperature
by the still-on heater.  Since it's biased negative, it emits, but since the
tube is cutoff, the electrons hang around the cathode - and the bombardment
of the cathode surface by the occasional electrode "wears it out" that much
faster.  The best screen saver would occasionally display SOMETHING every so
often, to let the cathode "clean itself."  

Best of all would be some way to reduce the heater voltage when the display
is in "screen saver" mode, so that the cathode would be "too cool to age",
but there's no good way to do that yet.  Until we get this feature from the
monitor folks, the best idea is to turn the display OFF when you're going
to leave it idle for a long period - definitely when you're going home for the
night.  The CRT is the shortest-lived part in the display by a wide margin,
on average, so the slight degradation caused to everything else by the once-
a-day thermal shock is worth it in tube life.


Bob Myers  KC0EW   Hewlett-Packard Co.      |Opinions expressed here are not
                   User Interface Tech. Div.|those of my employer or any other
myers@fc.hp.com    Fort Collins, Colorado   |sentient life-form on this planet.