How to Test an IR LED: 5 Easy Methods

If you want to quickly test an IR LED, the easiest method is using a smartphone camera. Because infrared light is invisible to human eyes, a phone camera can often detect infrared light and display it as a white, purple, or bluish glow on the screen.

For more accurate results, you can also test an IR LED with a multimeter, an infrared detector, or by checking voltage and circuit performance.

This guide explains several practical ways to determine whether an infrared LED is working and how to troubleshoot common issues.

Quick answer: The easiest way to test an IR LED is to point it at a smartphone camera while powering it correctly. If the camera detects a white, purple, or bluish glow, the IR LED is likely emitting near-infrared light. For a more reliable check, use a multimeter to verify forward voltage and polarity, then compare the result with the manufacturer's datasheet.

Why Infrared LEDs Are Difficult to Test

IR LED (Infrared Light Emitting Diode) emits light outside the visible spectrum, with 850nm and 940nm IR LEDs being among the most common wavelengths used in practical applications.

Unlike standard LEDs, infrared light cannot usually be seen directly by human eyes. An IR LED may appear completely dark even when operating normally. Whether an IR LED appears visible to a camera also depends on its wavelength, output power, the camera's IR filtering, and the testing distance.

That is why additional testing methods are required.

How to Test IR LED with a Smartphone Camera

This is the easiest and most commonly used testing method.

Why it works

Most smartphone cameras and digital image sensors retain partial sensitivity to infrared light. Although many phones include IR-cut filters, near-infrared wavelengths can still be detected.

Steps

1. Open your smartphone camera application
2. Point the IR LED directly toward the camera lens
3. Power the IR LED or activate the device
4. Observe the phone display

How to Interpret the Result

Some newer phones have stronger infrared filtering and may show weaker results.

Which IR LED Testing Method Should You Use?

How to Test IR LED with a Multimeter

Many users search for how to test IR LED with multimeter because it provides a quick electrical check.

Step 1: Use diode mode

Set the multimeter to diode mode. For a general reference on diode testing, you can also see Fluke’s guide to testing diodes with a digital multimeter.

Connect:

• Red probe → anode (+)
• Black probe → cathode (−)

If the IR LED is functioning, you may see:

• Forward voltage reading
• Small voltage drop
• Weak camera-visible light

Typical IR LED forward voltage

These values are general reference ranges, not universal specifications. Forward voltage varies with wavelength, chip design, package, forward current, and power rating. Always use the manufacturer's datasheet as the final reference. If you are not familiar with parameters such as forward voltage, wavelength, radiant intensity, or beam angle, see our guide on how to read LED specifications.

If measured voltage is significantly outside these ranges, the IR LED or drive circuit may be damaged.

Important note

A multimeter confirms electrical conduction but cannot fully prove infrared light output.

For best accuracy, combine this method with the smartphone camera test.

How to Check IR LED Polarity

How to Detect Infrared Light

Using an Infrared Detector or Photodiode

For engineering applications or production testing, dedicated infrared detectors provide more accurate measurement. For more information on infrared detector technologies, refer to Hamamatsu’s infrared detector resources.

Common detector types:

• IR photodiodes
• Photoresistors
• IR receiving modules
• Commercial infrared detectors

When infrared light is present, the detector produces a measurable response:

• voltage change
• resistance change
• signal output
• indicator activation

Advantages:

✔ Higher accuracy
✔ Quantitative testing
✔ Suitable for production environments

Disadvantages:

✘ Additional equipment required

Testing Through Application Function

In many systems, infrared LEDs can be verified through actual operation. An IR LED is an infrared emitter, while an IR sensor or receiver detects infrared radiation. If you need a deeper explanation of the receiver side, see how infrared sensors work in active IR and PIR systems. When troubleshooting a complete IR system, test the emitter and receiver separately before evaluating the entire circuit.

Examples:

Remote controls

Point the remote emitter toward a smartphone camera while pressing buttons.

A flashing white or purple light indicates operation.

IR beam sensor systems

Break the infrared beam and verify whether receiver output changes.

Security camera illuminators

Test the camera in a dark environment and confirm night vision activation.

Functional verification often provides fast confirmation without special tools.

IR LED Troubleshooting: Why Is It Not Working?

If an IR LED is not working, check the power supply, polarity, connections, and drive conditions before replacing the component.

Power or connection issue

Check for:

• Low or unstable voltage
• Loose wires
• Broken solder joints
• Damaged connectors

Reverse polarity

IR LEDs are polarized devices. Incorrect orientation can prevent the LED from operating. Check the anode and cathode against the manufacturer's datasheet.

Resistor or drive issue

A missing or incorrect current-limiting resistor can cause insufficient or excessive current. Excessive current may permanently damage the LED.

LED damage

Possible causes include:

• Overcurrent
• Overheating
• ESD
• Excessive reverse voltage
• Physical damage

If the LED has the correct polarity and electrical input but produces no detectable infrared output, test it with a suitable IR detector and compare the results with the manufacturer's specifications.

 

Quick IR LED Testing Checklist

✔ Use smartphone camera first

✔ Verify polarity direction

✔ Measure voltage

✔ Test using multimeter diode mode

✔ Check resistors and solder joints

✔ Confirm sufficient current supply

✔ Test actual application function

Safety Notes When Testing IR LEDs

Although infrared light is invisible, high-power IR LEDs can still create eye safety risks.

Always avoid:

• staring directly into active IR LEDs
• close-range exposure
• operating high-power emitters without protection

For industrial systems, follow IEC 62471 photobiological safety recommendations.

Do not assume that an invisible IR LED is harmless simply because you cannot see the emitted light.

FAQ

How do I know if my IR LED is working?

Point the IR LED toward your smartphone camera. A working infrared LED usually appears as a white or purple light source on the screen.

Can a multimeter test an IR LED?

Yes. Diode mode on a multimeter can indicate whether current flows through the IR LED, although it cannot fully verify infrared output.

What voltage should an IR LED have?

Most IR LEDs operate between approximately 1.1V and 1.7V depending on wavelength and current.

Why can't I see infrared light?

Infrared light exists outside the visible spectrum and cannot be detected by human eyes.

Can IR LED fail even if voltage exists?

Yes. Internal damage may allow current flow while preventing infrared light emission.

How do I test an IR LED without a multimeter?

Point the powered IR LED toward a smartphone camera. If the camera detects infrared light, the LED may appear as a white, purple, or bluish glow. If nothing appears, try another phone because some cameras have stronger IR filters.

Why does my IR LED show voltage but no light?

Voltage alone does not confirm that an IR LED is producing infrared output. Check the polarity, forward current, and drive conditions. Also try another camera or an IR detector, as some cameras cannot detect certain infrared wavelengths effectively.

How do I test a 940nm IR LED?

Use a smartphone camera for a quick check, then use a multimeter to verify polarity and forward voltage. For more reliable testing, use an IR detector and compare the LED's operating conditions with the manufacturer's datasheet.

Conclusion

Testing an IR LED can be as simple as using a smartphone camera, while a multimeter and IR detector provide more reliable results. Checking polarity, voltage, current, and circuit connections can help identify common IR LED troubleshooting issues.

For engineering and OEM applications, always compare test results with the manufacturer's datasheet to ensure the correct wavelength and operating conditions.

Need help selecting the right IR LED for your application? Contact Houkem for datasheets, samples, wavelength recommendations, and OEM/ODM solutions.