Date:         Tue, 18 Sep 2007 14:51:10 -0700
Reply-To:     David Kao <dtkao0205@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Kao <dtkao0205@YAHOO.COM>
Subject:      Re: 3Watt LED?
Comments: To: Pensioner <al_knoll@PACBELL.NET>
In-Reply-To:  <HHEAJIOMDPBGGCKHACGJCEMECNAA.al_knoll@pacbell.net>
Content-Type: text/plain; charset=iso-8859-1

3 AAA cells will last from 10 to 20 hours. Not great but far better
than bulb type flash lights.

Yes, 4.5 volt and 700ma. So it's not really 3 watts, rather 2.2 or less.
Brightness is about 200 - 250 lumen. But this can vary depending on each
individual LED. Some better and some poor, although same LED. This is why
you don't want to connect them in serial. They need to operate at a narrow
and fairly high power level. Less power the light output drops quickly.
More power will burn them out.

When connected in serial I have seen voltage vary from 3.4 volt to 5.3 at
a reduced current level. In this case by increasing to 700 ma the one gets
5.3 volt will burn out within a minute, instead of 20,000 hours.

David






--- Pensioner <al_knoll@PACBELL.NET> wrote:

> I wonder how long this device runs on three AAA cells.  An AA cell is
> ~1.6A-Hr at ~1.5VDC.  Two of these running a 3V Led array would run for only
> ~1.5 hr before falling out of operating specifications.  TAANSTAFL applies
> here.
>
> If the device is a 4.5 V device using three series cells the result would be
> essentially the same.
>
> Maybe the LED device should be spec'd in lumens rather than watts.  Lumens
> are light output.  Watts are electrical power requirements.  However if it
> does draw 3W, the above will hold true.
>



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