🚀 go-pugleaf

I've had my share of woes with Radio Shack products but this time they 
have a winner!

RS catalog # 276-087 "Super-Bright LED" ($1.69, from Japan) is truly 
impressive.  It's rated 2000 mcd output at 20mA (red; wavelength 660 
nm).

My friend John Halleck says that it's more robust than similar LEDs 
made by Panasonic and sold by Digi-Key, and can take 70mA continuous 
current (see below).

At 40mA the direct main beam is too bright to look at comfortably, and 
leaves an afterimage. It projects a visible spot on a white wall five
feet away in normal room light.

This LED with series resistor, plugged into Mini-Mag (tm) flashlight 
(two AA-cells) makes a long-duration emergency light. (Pilots and 
sailors take note.)  I plan to use one to illuminate an automobile 
instrument. Maybe I'll use one with LM3909 to fake a car burglar-
alarm.

It's a far cry from the first LED I ever saw, circa 1966!  A Hewlett-
Packard salesman demonstrated one mounted in a velvet-lined jewelry 
box made to hold a ring. It was gold-plated and beautiful, though 
barely visible, and cost $70.

   Excerpts from e-mail from John Halleck (nahaj@cc.utah.edu):

They are a little more robust in the face of overvoltage than the 
Panasonic ones.  (Yes, I am surprised they are not the ones I thought 
they were.) They are as bright.

My backup cave light is nine of them (70ma) at 6 volts (4 AA's).  
Really bright! (Grouped as 3 paralleled groups of 3 in series in 
series with a 10-ohm resistor. The resistor is only needed to limit 
current with new batteries; after an hour or so you can switch it out)
The resistor may be omitted if you don't mind running at or slightly 
above the max rating when the batteries are new.

The 3 x 3 array makes one HELL of a bike tail light. It's painful to 
look into at 10 feet.

> Do you leave the leads long for heat sink?
No, I mount them on a perf board, and clip the leads short. (Zero 
heat sinking.)

The  RS  LEDs  have a number of differences  from  the  Panasonic 
equivalents that I've tried.

The voltage drop is higher.

The tolerance to over-current is MUCH higher.  30mA is the published 
Absolute Maximum; I have run them up to 175mA for 30 seconds.  At this 
level, they are very bright but they are permanently damaged. After 
the damage they have a higher internal resistance, but still 
functioned. This same test totally fried the Panasonic LEDs; the RS 
ones survived. RS LEDs were warm but not hot at the end of the test.  
After the test, I compared them with non-abused ones.  The light 
output was down (visually) about 50 %. Current was reduced for any 
given voltage.

I cannot get any information as to their lifetime.

They  are  FANTASTIC hooked to a LM3909 and flashing.  In a  dark 
room they  will put a visible spot on a wall 20 feet away.  

No idea of the manufacturer or type number.  It does not seem to be 
any of Panasonics.

Update:  The damaged LED's were put back in service.  (I am doing 
battery and LED lifetime tests.   The damaged ones were (visually) 50% 
down compaired to the non-abused ones when put back in service. They
were 
a LOT less than 50% of the brightness after another 24 hours, and one 
of the three has now failed totally.   Walt Howard from our local EE 
dept theorizes that there was less active area after the abuse, 
causing the current density in the remaining area to skyrocket when 
the original 20ma was restored.

   -Nahaj

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Frank Reid     W9MKV
reid@gold.bacs.indiana.edu
Radio Shack's mailing list - Just say no!