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From: shirriff@sprite.berkeley.edu (Ken Shirriff)
Newsgroups: sci.electronics,alt.folklore.urban
Subject: Re: Turning off lights
Message-ID: <1991Mar23.231705.8161@agate.berkeley.edu>
Date: 23 Mar 91 23:17:05 GMT
References: <1991Mar18.213242.10174@mcs.anl.gov> <18627@milton.u.washington.edu> <1991Mar23.203207.6686@pixar.com>
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I did some more research on turning on lights.

From the IES Lighting Handbook:
A 100 watt general service incandescent light at 120V has normal
current of .835A.  It has theoretical inrush current of 17.9A.
Current reaches the normal value in 0.10 seconds.  (They compute
the theoretical inrush current from the hot-to-cold resistance
ratio.  They say the real inrush current is less due to circuit
reactance.)

So as an absolute worst case, the inrush uses 17.9Ax.1s/.835A = 2.1 seconds
worth of electricity.  (Assuming peak inrush current for the entire time
until current falls to normal level.  This isn't realistic, but I'm looking
for an upper bound.)

Therefore, the power surge when you turn on an incandescent light bulb
uses less than 2 seconds electricity.  (Probably a lot less.)  So "Dear
Abby" is only off by a factor of 300.

Ken Shirriff			shirriff@sprite.Berkeley.EDU