XPost: uk.rec.driving   
   From: no@spam.com   
      
   On Wed, 24 Apr 2013 08:33:48 +0100, Daniel47@teranews.com  wrote:   
      
   > Major Scott wrote:   
   >> On Tue, 23 Apr 2013 16:58:35 +0100, Dave Plowman    
   >> wrote:   
   >>   
   >>> In article ,   
   >>>    Major Scott  wrote:   
   >>>> > Pulsing an LED is a way of getting a higher light output from it   
   >>>> > without overheating. Overheating an LED kills it in short order.   
   >>>   
   >>>> Take for example the brake/tail lights.  These are often pulsed for tail   
   >>>> and on for brake.  So what you said doesn't make sense.  Anything less   
   >>>> than full voltage on (as for brake) will be lower heat.   
   >>>   
   >>> LEDs are current, not voltage, driven.   
   >>   
   >> When there's a series resistor, then you can think of them as voltage   
   >> driven.  Anyway electronics to lower the current can be made without   
   >> pulsing.   
   >   
   > No, the series resistor merely determines the maximum current that could   
   > flow through the LED.   
      
   Take for example a 6 volt DC supply connected to an LED in series with a 200   
   ohm resistor.   
   2V 20mA at the LED, 4V 20mA in the resistor.   
      
   Now change the supply to 4V.   
   2V 10mA at the LED, 2V 10mA in the resistor.   
      
   Lowering voltage will dim the LED.   
      
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