Date:         Mon, 29 Jul 1996 14:01:59 CST6CDT
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         "Dan Houg" <fairwind@northernnet.com>
Subject:      basic electronics/deer poaching


On 29 Jul 96, Harvey Chao wrote:

> go back to my "critical things" of the previous post:
> the critical things here are:  
> 1)  Does the LED light to an acceptable brightness?

it will when i'm done with it!!  LEDs make an incredible flash for 
their size-- but only once :)  but seriously, 80ma produce very 
bright light.  i think 50 would do nearly as well.

> 2)  Is the LED gettting excess current that could cause it to fail
> prematurely, and  - do we care if it fails prematurely, and if so, HOW
> prematurely?

when this thing finally ends up in my application (reading light), i
will tailor the voltage drop to yield about 50ma current with the
engine off.  and i expect to do this by hooking LEDs in series
instead of the dropping resistor.

and as far as premature failure goes... maybe it will cut down the 
10,000 hour rated life to 8,900 hours.  i could finish War and Peace 
*plus* The Dilbert Collection at that rate.

> 3)  Is the 1/2 watt resistor running too hot - to the point where it could
> fail and be a fire hazard???

well, as i said, i think the way to go will be to drop voltage with 
more LEDs... but if i did use a resistor (which i may when i actually 
get down to spending $4 per LED) i will hook it up, check the current 
and monitor for heat before permanently installing.

Here's ANOTHER angle---  how long would 2 AA alkaline batteries in series run 
@ 50ma???  i have NO idea of what they can put out and for how long.  

these LEDs really are bright enough to use as a flashlight....... 
hmmmm.

-dan