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'[EE]: White LEDs'
2000\08\25@063842 by Russell McMahon

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The following comment from a  friend may be of interest.
A torch using eg a single Alkaline AA cell and an inverter with an 80% mean
efficiency (hard but not impossible) would give around a 25 hour continuous
battery life. Efficiency is said to be several times that of fluorescent
which in turn is several times that of incandescent bulbs.

RM
__________________________________________________________

Have purchased several 5,600 mcd white LED's from DSE (cat Z3981, $9.95 ea
retail).

They come with a brief data sheet which includes a prominent warning
regarding possible eye damage.  This warning is not "nannying"  - these
devices are truly stunning in terms of brightness at 20mA If.  They are even
uncomfortably bright at 2mA, and usably visible (as a status indicator) at
50 uA.

I predict (as I'm sure others already have) that the days of incandescent
bulbs (and probably gas-discharge type lamps) are now numbered.  Someday all
light sources will be phosphor-coated LED's.  Buying shares in Nichia may be
a smart move.

They do however have one limitation at present (other than cost).  Their
emission is broad-spectrum but far from flat  - a narrow peak at 460nm (100%
relative intensity)
with a wider peak at 560nm (50% relative intensity) separated by a minima at
500nm (25% relative intensity).  Emission is minimal below 425nm and above
750nm.  They can be filtered for other colours but the results will vary
depending on the actual colour sought (don't believe people who say you
can't filter tham at all  - they have soft minds).

Actually they have another limitation  - forward voltage drop of around
4.0V.  This precludes their use in 3V systems (without trickery) and makes
makes current stability in 5V systems doubtful if you just use a resistor
for current limiting.  You could however make a very nice torch using one of
the Linear Tech low-Vin switchmode inverter chips (running in constant
current output mode) and a 1.2V or 1.5V battery.

Regards,

Ken Mardle

Applied Digital Research Ltd.  Tel    : +64 9 415-2514
P.O. Box 6480                  Fax    : +64 9 415-3514
Wellesley St                   Mobile : +64 25 879-648
Auckland                       E-mail : spam_OUTkenmarTakeThisOuTspamadr.co.nz
NEW ZEALAND                    WWW    : http://www.he.net/~adr/
                                       http://www.acqura.com

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2000\08\25@103353 by Nicholas Irias

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I have a white LED keychain light, and it uses a 3volt watch battery with no
dropping resistor.  So running white LEDs from 3volt logic ought to be a
piece of cake.  Running them at less than 4 volts must reduce brightness
some, but they are still quite bright at 3 volts.

{Original Message removed}

2000\08\25@150205 by Henry Carl Ott

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  I think you'll find that there are actually TWO cr2016 batteries in your
white (or blue) led key chain flashlight. The ones with red or yellow leds
typically use a single cr2032.
 But you are right they don't bother with a current limiting resister,
instead relying on the internal resistance of the lithium batteries.

 There is currently a very slick white led flashlight that runs on a
single AA battery for auction on EBAY. It incorporates some sort of voltage
doubler/tripler.
  Unfortunately the price is a little high for my tastes.



At 07:33 AM 8/25/2000, you wrote:
>I have a white LED keychain light, and it uses a 3volt watch battery with no
>dropping resistor.  So running white LEDs from 3volt logic ought to be a
>piece of cake.  Running them at less than 4 volts must reduce brightness
>some, but they are still quite bright at 3 volts.
>
>{Original Message removed}

2000\08\25@190016 by Mark Willis

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Russell McMahon wrote:
<snip>
> Have purchased several 5,600 mcd white LED's from DSE (cat Z3981, $9.95 ea
> retail).

URL for DSE, anyone?  (I try to bookmark them all.)

<snip>
> I predict (as I'm sure others already have) that the days of incandescent
> bulbs (and probably gas-discharge type lamps) are now numbered.  Someday all
> light sources will be phosphor-coated LED's.  Buying shares in Nichia may be
> a smart move.

Would be if they weren't privately owned, that is!  <G>

Interesting parts.  Visible at 50uA, NICE!  Little pricey ($10 >>
$0.10!) - in time they'll be cheaper <G>

 Mark

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2000\08\25@191725 by Jinx

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> URL for DSE, anyone?  (I try to bookmark them all.)

http://www.dse.co.nz

http://www.dse.com.au

and the competition

http://www.jaycar.com.au

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2000\08\27@170828 by Lance Allen

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On 25 Aug 2000, at 14:38, Russell McMahon wrote:

> The following comment from a  friend may be of interest.
> A torch using eg a single Alkaline AA cell and an inverter with an 80% mean
> efficiency (hard but not impossible) would give around a 25 hour continuous
> battery life. Efficiency is said to be several times that of fluorescent
> which in turn is several times that of incandescent bulbs.
>
I read that there has just been a quantum leap in LED light output
(in the lab right now). This has been achieved by etching the LED
with a random/irregular surface (like a Manhatten skyline) that
dramatically reduces the internal reflection losses.There is some
hideously low % of light that escapes from a LED compared to what
is actually generated internally.
The future looks.......... bright.

(Shoot that man for making criminally bad puns)
_____________________________

Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand

http://www.psych.auckland.ac.nz

_____________________________

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