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From: mjy@sdti.UUCP (Michael J. Young)
Newsgroups: comp.misc,comp.terminals
Subject: Re: Does Turning off PC's everyday do any real damage?
Message-ID: <241@sdti.UUCP>
Date: 8 Mar 88 19:01:00 GMT
References: <1727@ssc-vax.UUCP> <120@ftp.COM>
Reply-To: mjy@sdti.UUCP (0000-Michael J. Young)
Organization: Software Development Technologies, Sudbury MA
Lines: 51
Keywords: I hate Keywords

In article <120@ftp.COM> dab@ftp.COM (Dave Bridgham) writes:
>
>	With powering off PC's, one of the important things to
>consider is the thermal cycling of the picture tube filament.  I
>havn't read of any studies with picture tubes, but I have with with
>flourescent lights.  Many places leave their lights on all the time on
>the belief that this prolongs their life.  It was found that this is
>not necessarily the case.  If the lights are on continuously for 10
>hrs a day and off the rest of the time, they lasted longer than if
>they were left on 24 hrs a day.  I'm not sure how well the results of
>the lights study transfers to picture tubes, but the problem is
>basically the same.

The analogy of florescent lights is an appropriate one.  Turning florescent
lights on and off may indeed shorten their effective life.  But that doesn't
mean it's cost-effective to leave them on.  For example, say you have a light
that has a rated lifetime of 1000 hrs.  Cycling the power once a day as
suggested above shortens its lifetime by 30%.  But the light is only needed
10 hours a day.  The other 14 hours, there is nobody around to care if the
light is off or on.  Then the USEFUL life of the light that is left on
continuously is only 10/24, or 42% of 1000 hours.  The total number of
useful days of light is only:

                  1000 hr/day
                  -----------  = 42 days
                   24 hr/day

But the light that is cycled each day has a USEFUL life of:

                 1000 hr * .70
                 ------------- = 70 days
                   10 hr/day

In effect, the light lasts longer because it is turned off and on, even
though it technically isn't "good" for it.  The same can be applied to
computers, disks, and CRTs.  I've never heard of real studies to see
what the actual numbers might be, though.

>	The other thing I would be concerned about is spinning up and
>down hard disks.  This is when most head crashes occur.  I don't have
>any hard information about that though.

On the other hand, leaving the disk on could result in increased wear
on the bearings.  I doubt if this is much of a concern, though.

With all that said, you might think I turn my computer off at night.
Actually, it runs 24hrs/day, since I get my news feed at night.
-- 
Mike Young - Software Development Technologies, Inc., Sudbury MA 01776
UUCP     : {decvax,harvard,linus,mit-eddie}!necntc!necis!mrst!sdti!mjy
Internet : mjy%sdti.uucp@harvard.harvard.edu      Tel: +1 617 443 5779