dcbwhaley wrote:
.

Fluorescents get about 100lm/W, the very best white LEDs, run under laboratory
conditions get around 30lm/W, and incandescents get under about 20lm/W.

So, about 50%, 15%, and 10%.

Why do torches and headlamps with LEDs have such an improved battery
life when compared with those with incandescent bulbs? It is
certainly more than the 50% that your figures would suggest.

It's generally because small incandescent bulbs really, really suck.
They only really start to perform well at sizes of around 5W or so.

Plus - if a LED is running with a flattish battery, it produces usable
light, where a bulb just goes to a useless red glow.

Also, compare the beam patterns.
In many cases, the LED torch may produce more light, but over a narrower
area, which uses less energy.

Unfortunately, this is an area where there is a whole lot of lying going
on.

'100W' replacement spot bulbs that produce a tiny dot that's as bright
as the original light, for example, and rapidly dim over days of
on-time, because they overheat.

But even the makers of the most efficient LEDs - for example
http://www.luxeonstar.com/ don't claim more than about 1.5 times the
efficiency of large filliment bulbs, and that under somewhat optimistic
conditions. (marketing lies)