XPost: uk.rec.driving   
   From: ianREMOVETHISjackson@g3ohx.demon.co.uk   
      
   In message <53411d7de7dave@davenoise.co.uk>, Dave Plowman   
    writes   
   >In article ,   
   >   Major Scott  wrote:   
   >> >> 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.   
   >   
   >Why would you have a 'series resistor' if they are pulse driven?   
   >   
   >But in any case it is irrelevant. It's the current they are driven with   
   >that matters - not the voltage.   
   >   
   Nothing is really only 'current driven'. It's more correct to say that   
   LEDs need to be driven from a power source which provides a fairly   
   well-defined current. Even when you drive them with pulsed current, the   
   amplitude of the pulses will be determined by the voltage producing the   
   pulses. At any instant, the power dissipated in the LED is simply the   
   product of the voltage across it (typically 2V, depending on the colour)   
   and the current flowing through it. When pulsed, the average power is   
   also determined by the mark-space ratio of the pulses.   
   --   
   Ian   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)