LED torches

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LEDs are continuously improving.  In 1999 their efficiency surpassed that of conventional incandescent tungsten torch bulbs, and in 2006 Cree demonstrated white light LEDs with a better efficiency than fluorescent tubes.  The figure to look for that tells you how much light is produced is the "LUMENS" (lm).
Seoul Semiconductor have recently (Feb 08) brought to market the Z-Power LED P7 series a single LED package providing the worlds highest brightness of 900 lumens (90 lumens per watt) and lower power (1W) leds in development are now achieving up to 160 lumens per watt. (lm/W) (Jan 2009)

By comparison our "low energy" light bulbs deliver 60 lm/W, and quartz-halogen headlight bulbs a puny 20 lm/W.  (A lumen is the standard unit for measuring total light output, and a candle produces about 13 lumens)  These developments mean LED's are now well suited to application in torches.

So if you are loooking for a new torch here are some LED types to look out for:

The SSC P7 series LED's produce up to 900 lumens using 10 watts of power.
CREE MC-E series LED's produce up to 480 lumens using 4 watts of power.
CREE Q5 series LED's 230 lumens  using 3.4 Watts of power.
LUXEON K2 series LED's - 250 lumens  using 5 Watts of power.
SSC P4 series LED's - 160 lumens  using 3 Watts of power.
CREE Q4 series LED's - 160 lumens  using 3 Watts of power.

These figures are a guide only as the actual output will depend upon the drive current, the "bin" of the led, and the optics of the torch.  However some manufacturers are claiming ridiculously high outputs, and sometimes overdriving the led's by feeding excessive current to them.  Naturally this shortens their life, and also means the light will run for less time from the battery.

Note also you dont get something for nothing.  Ignore claims of several hours of use at full output.  If you want lots of light AAA cells will not last long.  For best results look for torches that use "18650" protected lithium cells.  Searching ebay for 18650 Q5 will get you a decent torch with batteries and charger for about £10 inc p&p!

More information here http://www.durhambats.org.uk/about_torch.htm

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