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you won't know. you will just know that one of them activated the SPAD

@profrobotix Not a SPAD then?

@@jagmarcLED as SPAD can only be used as a low-efficiency photon counter. To isolate a single photon in a lab environment, you'll need a very high-end device.

@@profrobotix photomultiplier tube!

is it painted in vantablack? JK that is really cool, what you have a source that makes single photons? like...a...faucet for individual photons. You just dial it in add just enough juice and one photon pops out. Amazing to say the least.

It's a very inefficient <$0.1 SPAD compared to those >$1K research-grade models. still useable after proper calibration.

I haven't tried it because I don't have a power supply that goes up to the breakdown voltage of a blue, green, and non-GaP Red LED. Be careful because they are much higher than the ~20V I used.

Me too. My goal is to build a dirt cheap but reliable and reasonably sensitive radiation detector from stuff that you could find in scrapped equipment. This looks very promising ❤

Usually inferred ones, remember come back bring more information back to us.

LTL-4223 red LEDs work. They are very cheap, and today are sold everywhere for a symbolic price, like no more that 20 cents something for each. I bought 10 of them recently ( 1-2 days delivery for extra $8).

@@andrewvolunteer2185Do you know what the breakdown voltage for the LTL 4223 LEDs is? I am trying to replicate the experiment in the video with a few of those diodes and was having trouble recreating the situation. I think I might not have a high enough load voltage.

You will want to use ones with a 10nm or less peak emission bandwidth. The yellow ones have a very large bandwidth so the gain region would be highly diffused.

nice to know the LTL-4223 will work too

Well if your palm can block 500 kHz switching emf……

@@yeyuan6273 I meant the blinking light from flourecent tubes, probably HF drivers. Flesh of a hand is really suboptimal at blocking light, especially in the longer wavelenght of visible spectrum.

thats 50hz or 120 for old energizer, about 200 to 500 khz for morden switching one, he is meauring 20 to 40 counts per 50us, doesnt add up. and its typical guss. response regarding spike. and i dont think flourent tube use pwm to dim it@@Paxmax

@@yeyuan6273 Good points! Florescent drivers has gone thru the entire frequency spectrum really, depending on age the "HF drivers" started at 50kHz and has crept upwards the newer it is.

He did build a photodetector... and it detects the ceiling flourescent tubes alright 😁👍

It will have a photodiode transconductance region then you will hit the avalanche region. For LEDs this will very a lot. You would need to severely limit the peak current, but a high ohms resistor and a tiny capacitor, or even the intrinsic capatance of the LED itself should work. Follow the pulse with a JFET amplifier and sense resistor and go from there. ❤

You should look into sipms. But I don’t see the implementation in images as now. You can imagine that each and every pixels character has to be almost identical with each other to work. Or one pixel discharging will pull all the other pixels voltage to ground............. and that is why sipm is so fking expensive.

in principle yes. but impractical. you will need a large bias voltage and a register to collect the counts from each "pixel". you will need miniLEDs, or have a huge optical lens to project the image onto the LEDs.

Using a LED as a SPAD is simple, cheap (instead of paying hundreds or thousands) but not efficient, probably < 1%.

Is there a way you can demonstrate that it is does really have the capability to detect single photons? If you place a LED in a well lit room it will produce a current of 10uA or so. -- This would require a huge number of successful photon/LED interactions per second What may be happening here is the barrage of photons is slowly charging up the junction voltage until it reaches a breakdown; you can even see an RC charge curve before every breakdown event on your scope. One test that could be performed is place the LED in a dark room with a very low rate photon source ~dozens per second, and see if it's possible to detect if the source is there or not with your LED

That’s typically avalanche behavior of diode, it’s just one pixel, it’s not a sipm arrays, in this condition it’s long overwhelmed, so it’s the dynamic range its weaknesses is in not sensitive. Around 450nm, all silicon based ones quantum efficiency is around 40%. And yes it generates dark count due to thermal act, that’s why people invent sipm to achieve higher sin to noi ratios. I understand why he is jumping into the project, as one can do gamma spectrometry by a bpw 34( kind of doing it), that is 1 cents of cost compared with sipm chips, quite tempting. Again apd is a apd, if it’s working in Geiger model, it can detecte 450nm single photon quite well, actually bpw34 can resolve Photo numbers by pulse height, again the weakness is noises and dynamic range not quantum efficiency. As apd has to be quenched after each pulse it’s in dead time during discharge.

the LED is detecting single photons when given billions of photons. its efficiency is very very poor. but still a great demo!

@@zhenyuanyeo8386 Yes, that was total bullshit. :-)

Yes, I should've declared it as volatile.