[Shop-talk] Wiring a string of LED lights

[BJNoSHOV8]

Some of them do have resistors, it all depends on the LED that they are 
using and the battery configuration.  The Luxeon and Cree LED's have 
forward voltages of around 4-4.5V and up.  The cheapest of these that 
you can buy in stores run off of 3 AAA batteries, but as the batteries 
wear they can drop below the voltage required by the LED.  You can't get 
a good LED flashlight with just 2 AA, C or D batteries because the 
voltage isn't high enough, unless there is a boost circuit, and that 
makes the light quite a bit more expensive.  The new Maglite LED 
flashlights have a boost circuit, but they don't have a good means of 
dissipating heat so they are not as good as they could be.  The small 
police-type flashlights that use a pair of 3V Lithium batteries 
sometimes have resistors, or sometimes they just drive the crap out of 
the LED to get a little more brightness, but again the good ones like 
Surefire have circuitry to maintain the voltage right where the LED 
wants it.

> Led flashlights get away without an external current limiting resistor
> because they've got a big honking current limiting one in the battery.
> They also tend to use higher power drawing diodes.   But better flashlights
> have driving circuits that provide both current and voltage regulation.