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Dave Platt[_2_]

In article ,
wrote:

(If the cells are wired in parallel instead of series, then you are
correct, but that isn't very common.)

The three similar lights I have, they are in parallel. Which is why I probably wrongly assumed these were as well.

If they're in parallel, then they almost certainly aren't driving the
LEDs directly... a blue LED (with or without a white phosphor)
requires more than 3 volts in order to conduct.

So, if they're in parallel and are feeding only 1.5 volts into the LED
head, there is probably a voltage-boost circuit (e.g. a "Joule Thief")
which is stepping up the voltage before it reaches the LEDs.

And, the step-up comes at a cost. If the Joule Thief has to triple
the voltage before it feeds the LEDs, and the LEDs are drawing a total
of 100 mA at that voltage, then the Joule Thief will be pulling 300 mA
or more out of the batteries.

There ain't no free lunch, alas.

A simple series arrangement is less expensive, but it'll end up
wasting some power in a current-limiting resistor (unless the
flashlight makers go _really_ cheap) and the flashlight will slowly
dim as the battery runs down. A step-up circuit can feed a fairly
constant current through the LEDs until the batteries are almost
completely exhausted, and it allows for a "variable brightness"
feature (pulse-width-modulate the LEDs, or step up to a lower voltage
which results in a lower current).