How to jude whether IR led are working or not ?

IR leds are divided into near infrared and far infrared, usually near infrared led is at range of 780~1100nm and far infrared led is at range of 1100~2526nm,Wale can produce IR led range from 780nm to 1550nm.The visible light will be less when longer IR wavelength,the 780nm,808nm and 830nm IR wavelengths are visiable to naked eyes,but it’s hard to be seen when longer IR wavelengths such as 880nm,940nm,980nm.

How to know IR leds are working when it can’t be seen?

1.Use smart mobile phone camera.

This is the most common and easy method, just light up the IR led,then point it to mobile phone camera.

If IR led works,you will see purple or white lights at LED chip’s location on phone camera.

If you didn’t see it, maybe the IR led is not working,maybe also your phone's camera is completely insensitive to IR, or the LED's wavelength is too long for the sensor.

2.Use photoelectric sensor.

Align the silicon photodiode/transistor with the IR LED, and use a multimeter to measure the voltage (DC setting) or current across its terminals. If the voltage/current increases when powered on and decreases when powered off, it indicates that the IR LED is emitting light (avoid strong ambient light).

3.Use Infrared receiving module (such as TSOP38K).

If the IR LED is modulated at approximately 38kHz (such as in a remote control), a matched receiver head can output a decoded signal (measuring high and low level transitions with an oscilloscope or multimeter in low frequency mode); if the IR LED is not modulated or damaged, the receiving end will not respond.

4.Measure conductivity with multimeter in diode mode.

It can only determine whether there is an open circuit/short circuit (with a forward voltage drop of approximately 1.2–1.6V), but cannot confirm whether it emits light (electrical conduction does not necessarily equate to light emission, which may be due to aging or insufficient driving).

Notices:

1. The IR LED requires sufficient forward current (typically 20–100mA, depending on the model) and correct polarity; if used in a circuit, ensure that the driving transistor/IC is working properly and the current-limiting resistor is functioning normally.
2. Do not stare directly at the IR LED, as its high power may cause eye damage despite being invisible.
3. While testing with mobile phone camera,Some newer high-end phones may have stronger IR-cut filters, making the effect less noticeable.