Path: utzoo!attcan!uunet!husc6!bloom-beacon!mit-eddie!rutgers!iuvax!silver!commgrp From: commgrp@silver.bacs.indiana.edu Newsgroups: sci.electronics Subject: Super LEDs from RS Message-ID: <7200022@silver> Date: 22 Dec 88 15:44:00 GMT Organization: Indiana University CSCI, Bloomington Lines: 90 Nf-ID: #N:silver:7200022:000:3530 Nf-From: silver.bacs.indiana.edu!commgrp Dec 22 10:44:00 1988 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 -- -- Frank Reid W9MKV reid@gold.bacs.indiana.edu Radio Shack's mailing list - Just say no!