HELP, I have some leds that I can't identify. These leds were used in a factory to check the thickness of plastic bottles ( about a 1000 on a panel.) I thought they were Infrared. I connected one to my power supply and started at 11/2 volts ( I had a digital camera to view what it did as I thought it would be visible at the right voltage) and nothing happened till I reached 12 volts and it flashed red and shot it. Sooo than I thought it was UV did the same thing except had the led against a white paper (no blue light) and at 12 volts the same little red flash and another shot led. I decided to check a couple on my multimeter led tester and connected red to POS (little side)and black to NEG (big side) and got no reading but when I reversed the leads it has a reading all the time??? On a regular led it (the multimeter) flashes a reading and and than goes blank if it is good.PLEASE can someone tell me what I might have here as this is driving me crazy ha ha . I've googled every phrase I can think of to try to find something with no luck. PLEASE HELP JIM

 

Can you post a picture?

 

LEDs should light WELL before 12V. Even some high intensity LEDs have a forward voltage of only 4.5V.

LEDs are current sensitive. Most can only take 30ma or so. You went well beyond that.

Basically all you saw was the arc from the diode burning out and shorting. You need a current limiter.

If you did not see those diodes light before reaching 12v then chances are they are outside the visual spectrum.

 

They look just like a regular 5 mm LED and I know I should have used a resistor but when I'm in doubt I just start at low voltage (11/2 volts) and slowly increase till I can see light as this helps me decide what resistor to use. My power supply on a bright white LED with no resistor at 3 volts runs about 24ma. As far as being out of the visual spectrum, that's why I used the camara and white paper. The camara can see INFRARED and if it was UV the white paper should have had a BLUE look. I'm sorry but I don't know of any other LED's that don't lightup. I know the voltage for red, green, yellow,
blue,and bright white as I'v made many lights using these. What concerns me most is it reads like a silicon diode, blocking one way and reading the other. I get a reading with the POS probe connected to the cathode and the NEG probe connected to the anode??? I'm thinking it's not a light emitting diode ???? maybe just DATA ?? JIM

 

These are probably phototransistors. Most have dark plaastic to filter everything but ir. some are clear. They should block flow in negative direction and Might pop with a red flash if supplied with too much voltage. Try connecting cathode to ground and a nice 100k resistor and 12 volts. Then apply an ir source and measure voltage dorm anode to cathode.

 

Thanks GopherT thats what they are. I pulled up a data sheet and everything matches. I now have to find something to use 998 of these things for. ha ha I thought I had come in to a lot of good infared LED's. ha ha STUPID ME.
THANKS AGAIN JIM

 

As you said, it was used for some type of inspection station. You could rig something up to identify shapes, or even "password" protect something using gestures of had swipes across the surface like Window 8 does with the photo-password.