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From: tell@oscar.cs.unc.edu (Stephen Tell)
Newsgroups: sci.electronics
Subject: Re: Light Dimmer
Message-ID: <17840@thorin.cs.unc.edu>
Date: 30 Nov 90 03:44:28 GMT
References: <2570007@hppad.HP.COM> <1990Nov26.181619.9855@xrtll.uucp>
Sender: news@thorin.cs.unc.edu
Reply-To: tell@oscar.cs.unc.edu (Stephen Tell)
Organization: University Of North Carolina, Chapel Hill
Lines: 33

In article <1990Nov26.181619.9855@xrtll.uucp> rsnider@xrtll.UUCP (Richard Snider) writes:
>In article <2570007@hppad.HP.COM> lindner@hppad.HP.COM (Steffen Lindner) writes:

>While on the topic of problems, depending on the type of incandescent
>lights you are using, you probabbly will need some form of "preheating"
>current through the fillament in the bulbs if you want them to come on
>from some minimum setting without "popping" on.  This is becuase the
>current required to get the filament glowing from a "cold" condition is
>considerably higher than that which is needed to keep it glowing.

I note that its fairly common for lighting designers to build this into their
cues, preheating lamps that are to come on in the next cue at 10% power.
Unless the first cue is very dim, the soft orange glow is hardly noticable on
stage.  This actualy makes the transition happen faster, since the filament is
alreay somewhat warm.  The difference is definitely visible, and for
theatrical work, it depends on the effect you want.  It might also affect bulb
life, I suppose.

Tuning instructions for an analog dimmer I worked on once had you set things
so a 10% control input (1 volt) produced an 18 volt AC output, resulting in a
fairly dim but visible output from a 120 volt lamp.  When turning the control
up from 0, the dimmer output stayed off untill around 8 or 9%, and then came
up quickly to the "preheat" value.  I'm not sure if this was to ensure that
if the analog stuff drifted that 0% was always definitely off, or if it is
related to the cold-filament problem

>					.....Rich
>                                        rsnider@xrtll

--------------------------------------------------------------------
Steve Tell      e-mail: tell@wsmail.cs.unc.edu usmail:  #5L Estes Park apts
CS Grad Student, UNC Chapel Hill.                       Carrboro NC 27510
Former chief engineer, Duke Union Community Television, Durham, NC.