IR LED can be package as SMD LED type or Through-hole LED Lamps type.
Such as 5mm IR LED, 3mm IR LED or 2835 SMD LED, 5050 SMD LED ect.
To test an IR LED, for all the surface mount diode and DIP LED, we can follow these steps:
1. Connect the IR LED to a power source: Connect the positive leg of the IR LED to the positive terminal of a battery or power supply and the negative leg to the negative terminal. There will have a polarity mark on the infrared LED. When we check with SMD type, then it's the gap side of pins and it will be the longer or shorter pin when we check with DIP LED.
2. Use a multimeter: Set the multimeter to the diode test mode. Place the probes on the legs of the IR LED. If the LED is working, the multimeter will show a voltage drop.
3. Use a smartphone camera: Different with those colorful LED, infrared LED are normally invisible. In this case, we can use some tool that in our hands, which is the cell phone! Open the camera app on your smartphone and point the IR LED towards the camera lens. If the LED is working, you will see a faint purple glow on the screen.
4. Use an IR receiver: Connect an IR receiver to a microcontroller and program it to detect the IR signal. Point the IR LED towards the IR receiver and see if the microcontroller detects the signal.
5. Use an oscilloscope: Connect the IR LED to an oscilloscope and observe the waveform. If the LED is working, you will see a square wave with a frequency.