Quoting Richard Caldwell <rcaldwellie@yahoo.com>:

> Hi, I've always thought that LEDs drop 1.7 Volts due to the PN   
> junction depletion layer. I have a Surefire torch with a really   
> bright white LED and it takes two series 3volt batteries. Is this an  
>  LED with an internal PN junction that is somehow rated for 6v or is  
>  it an LED made of several series junctions? Can anyone explain?
>
> Thanks
>
> Richard

Some of the LED flashlights depend on the internal resistance of the
batteries to drop the voltage to the ~3.5V of the (blue) LED junction.

Best regards,
Spehro Pefhany
-- 
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