I’ve had a query about 12V near-infrared LED strip, especially 850nm LED strip.
You can see 850nm, but only just! 850nm is at the very edge of the eye’s ability to see. If you turn on the 850nm LED strip in a dark room, you will see a nice pale red glow. It’s red, but to our eyes it seems pretty dim. That’s good, that means it is working.
If your 850nm doesn’t produce a dim red, then it could be that you have been sent a 940nm strip instead of 850nm. That happens.
940nm isn’t visible to the human eye, no matter how dark a room you use. We just can’t see it. But you can feel it, as the little LEDs generate heat.
So turn it on and wait a while. If you can feel warmth coming from each LED, then it is probably 940nm.
If you were sold 850nm, there is no light and no warmth, try reversing the polarity, and connect the positive (+) LED lead to the negative (-) port in the connector, and vice versa. I know that you should be able to rely on the polarity being what it says, but sometimes the polarity is the opposite. I have no idea why. But it is worth a try providing, of course, that you are working with 12V LEDs.