A bit of fun - Can you guess what this is?

Can you guess what the 'thing' in the picture is? I will give you a couple of clues - 1, it is from the Soviet era. 2, It is a component that is widely used today, but the form factor has changed somewhat. 

 

Answers on a postcard. There are no prizes for guessing the correct answer, but you can live with the knowledge and glory that you were correct! 

Well done Radslug! You win 10 house points and a gold star! Whoo!   

I was looking for Light Emitting Diode, and you got that right. You weren't quite right with the part number, but not far off. The one pictured is a 3Л102Б (3L102B)

Here are some pictures tickling it with a little current.
 

 

I do have a АЛ102А (AL102A) too, pictured below. Mine seems to have some kind of frosting on the lens. Apparently some of the АЛ102А's had clear lenses, some frosted, although I don't have a clear one.
 

 

And here are the two side by side with the 3Л102Б on the left and the АЛ102А on the right.
 

I asked if the seller had any datasheet or info on them. This was his reply:

I do not have the original data sheet but these are the notes that I have on the 3L102B (3Л102Б):

•Light colour: RED
•Intensity: not less than 0.25 cd/m2
•Continuous direct voltage: not more than 2.8V
•Maximum spectral distribution: 0.69 m
•Maximum permissible continuous forward current: 20 mA
•Maximum surge current for a given pulse duration: 60 mA at 2 ms
•Maximum allowable reverse DC voltage: 2 V (max pulse reverse is the same)
•Maximum ambient temperature 70°C

There may be data sheets on line. I believe the other has similar specifications.

With regard to the diffuser on the АЛ102А, this is an intentional diffuser and is just a blob of epoxy on top of a piece of clear glass. If the epoxy is carefully removed you can see the LED behind glass like the other one. From the ones I have seen, the epoxy varies in colour from clear through a milky white to an off yellow. Quality varies considerably, with those with no air bubbles being clearer, and some which look like they have dirt or dust inclusions within the epoxy. I can’t recall the exact one I sent, but the comment about polishing sounds like it must be one of the clearer ones, as the finish on some of the ones with bubbles is quite rough. I haven’t tried polishing them.

Some Russian data about them:
https://eandc.ru/catalog/3l102b/
https://at-chip.ru/catalog/optoelektronnye-pribory-indikatory/svetoizluchayushchie-diody/3l102b-diod-svetoizluchayushij.html
https://eandc.ru/catalog/al102a/

I have also zipped up a bunch of high resolution images (some better than others) of the two LEDs and also included a vintage Letronix LED bubble display. You can download them here:
https://www.schmoozie.co.uk/download/vintage_leds.zip