Re: new LED torch (flashlight) bulbs more efficient?

From: Don Klipstein (don_at_manx.misty.com)
Date: 03/23/05 

Date: Wed, 23 Mar 2005 05:22:38 +0000 (UTC)

In article <0Vv%d.35481$3A6.4632@newsfe1-gui.ntli.net>, ghbt wrote:
>Do the new LED torches (flashlights) actually give more value for money from
>the batteries ( in terms of illumination per cost of batteries) than the
>previously developed small and bright xeon bulbs or the older ordinary torch
>bulbs?

  I say mostly yes, despite the LEDs having efficiency many times close to
or in the most optimistic case only about double that of incandescent and
halogen flashlight "bulbs"/lamps.
  Reason: Incandescents/halogens have a major loss of efficency as
battery voltage decreases while LEDs suffer usually much less. There is a
tendency of LEDs to have resistance increasing in response to lower
voltage while tungsten filaments have resistance decreasing as voltage
decreases. In addition, most white LEDs have their efficiency impaired
hardlt at all to not at all, more likely slightly improved if they are
moderately underpowered while tungsten filaments respond to underpowering
by having efficiency in light production decreasing about or more than
proportionately with power input as power input decreases.

  Result: Get two flashlights, as equivalent as possible except one has
an incandescent bulb and the other uses one or more LEDs, and they have
equal power consumption from good batteries.
  Turn them on and let them run, and when the incandescent one has dimmed
to the brightness of a cigarette idling in an ashtray, the LED one will be
100 or more times brighter than that even if only about 20-40% as bright
as with fresh batteries.

  There are some other situations where LEDs trule "rule". An exception
for now and probably at least a few more years is a practical and
econimical replacement of 40 watt and higher household incandescent lamps.

  Some more details in: http://www.misty.com/~don/lede.html

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