How we can know the IR LED is working?

Before we understand how to know the IR LED is working, we need to know, what is IR LED?

Infrared LED is a Light Emitting Diode that can converting light energy into electricity. And the wavelength are available in 850nm LED, 940nm or even more others like 810nm LED, 1450nm LED ect. When we package the infrared LED light as SMD LED type of through-hole LED, we can see there have a little chip inside. This is the chip that emits the wavelength when you pass the electrucity to it.

As we know, some of far red LED are invisible to human eyes. Which mean it's not same as the other coloful LED that you can see when it's working(They will emits different color when thwy work, such as, Yellow LED will emits yellow color when you light it up, and 625nm LED will emits red color when you pass the current to it.) Human eyes cannot see the infrared radiations, it is not possible for a person to identify if an IR LED is working. A camera on a cell phone solves this problem. The IR rays from the IR LED in the circuit are shown in the camera. So you can easy to see whether your IR LED is working or not!

There are 940nm LED and 850nm LED in the view of camera, It will emits a little pink color when we check if they work.