A picture might help.
Explain directly polarized and inversy (?) polarized. so we are all on the same page.
Directly polarized is, as in every electronic component: anode connected to positive of the power supply and cathode connected to the negative. Inverse polarized is the opposite. Perhaps I didn´t choose the correct expression because I´m not english.
A diode, either IR or Visible Light must not let pass any current if inverse polarized, and must have a 1.3 - 2-5 voltage drop if directly polarized.
You did not say if light exposure made any difference during the diode mode test.
You are right, I forgot. I just tested and there are no differences
5V @270 Ohm is about 18mA. some LED's take about 20mA to light up.
Right again. I tested with 3V3 at 0.20 mA. Multimeter measures 0,46 directly polarized, 0,60 inverse polarized. Still not light on.
If it is/was IR, how do you propose to know if it light up?
How are you determining this?
You will not be able to see the light from an IR emitter. You may be able to see it through a camera viewfinder but only dim.
What you really want is a camera without any IR filter. The NOIR Raspberry Pi is one such camera.
I use my mobile camera. It sees perfectly all the other IE LEDs I have, including a KY-005 module that has a LED that seems equal that the one I can´t identify, and all my IR remotes, including Arduino ones and TV one. The camera shows me the IR LEDs with a well differenced purple-pink light.
The voltage required to light an IR emitter is in the order of 0.7 to 1.4V so you don't need a higher one.
Tried again, with 1V5. Nothing
It wont, if it is a detector there will be an IR filter built in to stop that happening.
I´m not sure, but I think that that type of photodiode hasn´t any filter. Is a simple photodiode, not a phototransistor like V1838. (if it is a photodiode, of course). So natural light might affect it because natural light has IR waves too.
What forward voltage do you get at room temperature with 1 -- 10mA or so forward current?
5V with 1kOhm resistor gives us 5mA. So, second case:
- Polarizing at 5V with 1kOhm resistor. Multimeter at 20V range:
+ Directly polarized: Didn´t light on. Multimeter measured 0.28
+ Inverse polarized: Didn´t light on. Multimeter measured 0.34
Covering from light or exposing to it DIDN´T make difference.
Silicon photodetectors (0.7V) will be a lot less than a IR LED (1.1V), IIRC.
Photo emitters are not silicon, but a direct-bandgap semiconductor (normally). Of course
a photodiode doesn't have to be silicon, but many are.
I don´t understand what do you mean