Date: Mon, 22 Dec 2008 19:14:30 -0500
To: puptcrit-AT-puptcrit.org
Subject: Re: [Puptcrit] LEDs


The link that Tim gave [ 
http://www.mikesflightdeck.com/led_dimmer.htm ] was a great one.  The 
bottom line is that you can dim with a simple potentiometer, but the 
light will suddenly go on at a certain level, rather than dim up 
smoothly from being totally dark.

Note that there are two types of potentiometers.  Linear and 
non-linear (or sometimes called audio taper).  I wonder if the 
non-linear could be a better choice, but I have not played with 
it.  The data on the non-linear response of the LED is hard to find 
for a particular LED, so it is hard to design a circuit for the unknown.

The household bulb replacement LED bulbs are not dimmable because 
they have electronic power supplies.  They will actually fight your 
effort to dim them and try to keep the LED at the same 
brightness.  There are however, theatrical type LED fixtures that 
have a DMX interface.  This is a standard connection for theatrical 
dimmers.  They accept the DMX signal directly from the lighting 
control board and then internally they dim the LED itself.

The LED fixtures are great for puppeteers, because they are very 
rugged, and won't break during transport or burn out because the 
filament was jiggled while it was hot. But, they are just too 
expensive. In a few years, I am sure they will come down in price 
significantly.


Joe Dunfee  joe-AT-dunfee.com
Gordonville, Pennsylvania, U.S.A. 

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