What diode is this?

I recently found a very simple schematic to make a very simple Geiger counter. In the schematic, I can’t tell what type the diode is. Can anyone help me? Here is the schematic:

My guess is it's a general purpose LED to just show some light in addition to the click sounds.

-- The QuadRAM shield: add 512 kilobytes of external RAM to your Arduino Mega/Mega2560

I totally forgot that I didn't see any LED's on that. Thank you.

Probably a red led. Since the voltage drop over a blue or white led is large.

I recently saw GM tubes for sale on Ebay not too much money either, made and sold in Russia, low enough voltage so that a camera flash supply would work very well. Matter of fact I found a camera that had been dropped and kept it for the supply... just for safety I pulled a small coin out of my pocket and discharged the flash storage cap... It made a surprising snap. The camera had been dropped several days prior to my lucking upon it... A very good cap and from an AA battery too. Had I any interest I could have made a detector Very easily too. the most radiation I am exposed to is the several smoke detectors in the house and if there was a better way to do that those things would have long ago been disposed of. I do though have one I am going to "re-purpose" sometime... or maybe just toss it. even small amounts of radioactive stuff bother the hell out of me...