This is PAGE 2 of the 1970s exhibit. Go here for PAGE 3.




1970-1979: THE LED COMES OF AGE




This messy collage shows something that is probably
quite rare and may be a prototype that was never produced:
A near-1970 ORANGE LED!

This LED appears to have the same GaAs substrate and GaAsP emitting layer as a circa. 1970 red of the same design, but there's a lot more P (phosphorous) in this LED than in the red LED of the same design. This was apparently not an easy task.


Spectrographic analysis of this LED.
Ocean Optics USB2000 Spectrometer on loan from TWO-CUBED.

Here is the info I received from the local LED guru, Don Klipstein:

" Color more constant, no green peak, and efficiency dropping instead of increasing at low currents means probably the thin active layer is GaAsP with more P and less As than the 60 percent As 40 percent P used in original formula red. Could have been tough to make - more P than As is easier to make if the substrate is GaP (orangish, tan, brown, yellow, or maybe transparant) rather than GaAs (black). This one may be a prototype that did not go into production due to difficulty of making a 60 percent P 40 percent As layer on a GaAs substrate.
In the 1970's, GaAsP with mostly 60-40 (red-orange to orange-red) and 90-10 (amber-"yellow") P/As ratio came out on a GaP substrate."




This is one of the more unusual vintage LEDs I've come across.

The person who gave it to me claimed it had two dice (light emitting chips) but that one of them had burnt out. That's what I thought too, until I tried a little experiment. I connected it to power, and it glowed yellow. Then I hooked it up backwards, and it still glowed yellow. (!)

Turns out, this LED is a two-chip yellow, specifically made for use in an AC circuit. When one half of the AC cycle is on, one of the yellow LED chips glows; and when the other half of the AC cycle comes up, the first chip extinguishes and the second chip then lights.
Lather, rinse, repeat.

Both chips appear to be carefully matched, as they glow the exact same color and intensity as one another.




LEFT: A green LED packaged in an orange plastic case. Hmmmm...

RIGHT: Two variations of the TLR-147, an LED with a Fresnel lens top commonly available in Radio Shack stores (under the Archer label) in the late 1970s. These were meant to be installed where a wide viewing angle indicator was needed.




I came across another one of these metal-based LEDs like the famous "liquid nitrogen" model shown on the next page of this 1970s exibit.
Examining the LED shows the metal base is only a ring that encircles the base; you can see through the LED by looking at it from the base. It is still not clear what the metal ring was for; as in this configuration, it would make a lousy heatsink.




This early red LED uses a mask contact instead of a ball bond.
As a result, LEDs like this tend to have really strange looking LED chips.
Several types of mask contact LEDs are shown within the Museum's pages.




Here are some early contenders in the color LED war. Coming in red, yellow, and green; these LEDs manufactured by Monsanto found their way into lots of products and into lots of hobbyist's hands. They were not very bright, and could easily be drowned out in a bright room - but they were mysterious, fascinating devices that every tinkerer had to get their hands on.

For the colored LEDs in the first picture, the part numbers are MV5023, MV5222, and MV5322. If you're from Monsanto and think I have the part numbers assigned to the wrong colors, please feel free to write in and correct me. My original information was lost in an earthquake along with the computer that hosted it.

The one in the metal can is a GE part, and it is not known who made the clear one, though it may *possibly* be a Fairchild FLV-100. All five of these LEDs date from 1972 to 1973.







On the left is a two-chip yellow LED. As you can see, something interesting happens: when you increase the current, the LED visibly and dramatically changes color. At very low currents of a couple of milliamps or so, you get the nice orange you see in the far left. And as you increase the current to close to 30-40mA, you get the lime green on the right.


Spectrographic analysis of this LED at an If of ~28mA.

(Update 04-12-08): I've been informed by an LED expert on the east coast who's work I implicitely trust that this LED may in fact be one of those wily & elusive (and fairly rare) two-chip yellow LEDs!!! This LED uses a a GaP red chip and GaP green chip together (connected in parallel) to make yellow.


The odd looking LED on the right comes in a standard sized TO92 transistor case, but emits a very usable red light rather than acting like a typical transistor. One e-mailer speculates it may have been a voltage reference, but I'm not sure how to test that theory just yet. Another source (a former Motorola insider) thinks they were made by Motorola for Eastman Kodak to be used inside one type of camera. Cost effectiveness was the issue here; just use the existing machinery they had on hand for making transistors. The center lead is the cathode; and only one of the outer leads (for the anode) was actually used; the other doesn't connect to anything.







These amazing pictures show a very rare LED from Russia. Manufactured sometime between 1972 and 1973, this greenish-yellow LED gets its light from a chip of silicon carbide, a material most of you know as an abrasive substance used for sandpaper! Although fluorescence in SiC was discovered by Henry Joseph Round as early as 1907, this is the first known practical application for that ghostly greenish glow.

The LED's light output (from its normal "this side up" orientation) is only 10 ucd (that's ten microcandelas).

It came in two versions: a tiny pinhead-sized glass encapulated version like this for commercial use, and another in a sturdy metal can for military use.

I have a lot of additional information about this LED hidden away in various e-mails, but since a lot of damage was done in the Ash Wednesday earthquake, it will be a bit before I can pry myself away from disaster recovery and fetch that info.





This is PAGE 2 of the 1970s exhibit. Go here for PAGE 3.








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