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Light Emitting Diodes or LEDs are ubiquitous now, but I still remember riding my bike to Radio Shack and buying my first LED, checking the diagram on the back of the package, and getting a battery and a resistor to power it properly, going home, powering it up and seeing the deep red light from a semiconductor for the first time.

Question: When, where and why did humans first leave an LED on another astronomical body? Answer must attempt to address all three please!

⁺or astronomical body, though it will likely be a planet.

Related technology records:

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    $\begingroup$ Kudos for putting the resistor in the circuit. I'll never forget the smell of burnt LED. $\endgroup$
    – DrSheldon
    Commented Sep 21, 2020 at 5:50
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    $\begingroup$ @DrSheldon oh I did manage to burn it out within the week :-) $\endgroup$
    – uhoh
    Commented Sep 21, 2020 at 6:13
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    $\begingroup$ ... ah, destructive testing!! ;-) $\endgroup$
    – Fred
    Commented Sep 21, 2020 at 9:11
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    $\begingroup$ What about invisible LEDs enclosed within an optocoupler used in the circuit for interfacing? $\endgroup$
    – Uwe
    Commented Sep 21, 2020 at 11:40
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    $\begingroup$ @Uwe: That's what I was thinking. My guess would be a rotary encoder. $\endgroup$
    – DrSheldon
    Commented Sep 22, 2020 at 3:20

4 Answers 4

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July 20, 1976, Mars, Viking 1 lander.

In the article "Viking gas chromatograph–mass spectrometer" by Rushneck et al, Review of Scientific Instruments 49:817-834 (1978), section G (pp. 828-9) describes the GCMS's soil loader and pyrolyzer subassembly, which accepts a pulverized soil sample, loads it into an oven, and then seals and heats the oven.

As can be seen from Fig. 18, all mechanical functions are driven by two permanent magnet, incremental stepping motors: one drives the loader and carriage, and the other drives the clamp. ... Carriage and clamp positions are verified by signals from light emitting diode-phototransistor pairs on the carriage and clamp. These signals are fed into the GCMS computer and are used for verification of the proper function of the mechanism.

figure 18

This paragraph also directs the reader to further details in ref. 94,

Encoder Assy P/N 550050, 550052, [available from] Beckman Instruments Inc, Advanced Technology Operations, 1630 S. State College Blvd., Anaheim, CA 92806

but that may be a dead end by now.

quoted text

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    $\begingroup$ Fantastic work! Good job tracking this down! $\endgroup$
    – called2voyage ♦
    Commented Sep 25, 2020 at 21:34
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    $\begingroup$ We'll find out if they've made a badge for answering the same question a zillion times :-) ... I haven't quite given up hope for something earlier and lunar. $\endgroup$
    – Camille Goudeseune
    Commented Sep 25, 2020 at 21:40
  • $\begingroup$ Wow 1978, very nicely done! There's some information on the systems here. I don't know if there's any further mention of an LED but it contains many references. $\endgroup$
    – uhoh
    Commented Sep 26, 2020 at 6:10
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The Vega 1 balloon that entered the atmosphere of Venus on June 11, 1985, had LEDs on the anemometer:

The diameter of the rotating anemometer was 25 cm. The rotor was mounted on ball bearings, and rotation was monitored by a coded disk and two sets of light-emitting diode (LED) light sources and solid-state detectors.

Source: VEGA Balloon System and Instrumentation - Kremnev, et al.

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  • $\begingroup$ Very nice! I'm outside the paywall at the moment but Wikipedia's Vega_program; Balloon confirms. This will be hard to beat, but there might be earlier rotary encoder type things out there. $\endgroup$
    – uhoh
    Commented Sep 23, 2020 at 19:30
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    $\begingroup$ @uhoh Based on this paper comparing the operation of a laboratory facsimile camera to the Viking facsimile camera, it seems likely that the Viking facsimile camera had an optical encoder. However, the paper does not directly say so, and I can't seem to find any source that does. ntrs.nasa.gov/citations/19750007868 $\endgroup$
    – called2voyage ♦
    Commented Sep 24, 2020 at 20:27
  • $\begingroup$ I've confirmed your intuitions about encoders, or at least limit switches. New answer. (What a fun puzzle! Thanks, uhoh.) $\endgroup$
    – Camille Goudeseune
    Commented Sep 25, 2020 at 21:29
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July 20, 1976, Mars, Viking 1 lander.

(You're really not going to like this one.)

The lander's cameras included an array of 12 photodiodes to measure various things. One reference even plots each photodiode's spectral sensitivity; the abstract of another paper gives enough evidence for their existence.

But every photodiode also acts as a (rather inefficient) LED. QED!

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    $\begingroup$ But photodiodes are made from the wrong materials to be a LED. The recombination of holes and electrons produces heat instead of photons, $\endgroup$
    – Uwe
    Commented Sep 22, 2020 at 22:16
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    $\begingroup$ And heat is made of...? OK, you hadn't asked for 380 to 700 nm. I'll happily delete this answer, as I still have some leads for the 70's. Were we in the International Obfuscated C Code Contest of yore, this would vie for the award Best Abuse Of The Rules. $\endgroup$
    – Camille Goudeseune
    Commented Sep 23, 2020 at 1:57
  • $\begingroup$ If they had been III-V junctions, then yes I think if you forward bias them they will make some light. The abstract says that they are silicon photodiodes which means that non-radiative recombination will strongly dominate. I think if you forward bias a silicon photodiode that is duct-taped to the front of a photomultiplier tube and you are counting individual photons, you will see some. But you'll need to use a direct band-gap III-V LED to see with. A silicon photodiode is a closer relative to the silicon solar cell than to an LED* in my opinion. $\endgroup$
    – uhoh
    Commented Sep 23, 2020 at 2:02
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    $\begingroup$ I think most silicon photodiodes can even be run in the photovoltaic mode. They will function as PV cells fairly well, but not as efficient as junctions optimized to be photovoltaic cells for the efficient generation power. Space: Has direct band gap photoemission from III-V solar panels on spacecraft ever been detected or reported?, Physics: Do III-V based photovoltaics “glow” (photo-luminesce) when illuminated but not loaded? $\endgroup$
    – uhoh
    Commented Sep 23, 2020 at 2:05
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    $\begingroup$ Nonetheless I admire you work here! It's similar to what I did here :-) $\endgroup$
    – uhoh
    Commented Sep 23, 2020 at 2:09
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May 25, 2008, Phoenix Mars Lander. (Surely there's an earlier lunar example?)

The Robotic Arm Camera took an image of the Robotic Arm scoop using its red LED (Light-Emitting Diode) lamp.

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