An IR LED (Infrared Light-Emitting Diode) works by converting electrical energy into infrared radiation through a semiconductor junction. It operates on the same basic principle as a visible LED, but its semiconductor materials are designed to emit wavelengths mostly beyond the range visible to the human eye.

Common IR LED wavelengths include 850 nm and 940 nm.

How an IR LED Produces Infrared Light

An IR LED contains a P-type and N-type semiconductor, forming a P-N junction.

When the LED is forward biased:

1. Current flows through the LED.
Electrons move from the N-type region toward the junction, while holes move from the P-type region.

2. Electrons and holes recombine.
At the active region, electrons fall into lower-energy states and recombine with holes.

3. Energy is released as photons.
The semiconductor's bandgap determines the energy—and therefore the wavelength—of those photons.

4. Infrared radiation leaves the LED package.

The basic process can be summarized as:

Electrical Current → Electron-Hole Recombination → IR Photons

Why Can't We See IR LEDs?

The human eye generally responds to wavelengths of approximately 380–780 nm, with the exact limits depending on sensitivity and conditions.

IR LEDs operate at longer wavelengths.

For example:

An 850 nm LED may produce a faint red glow at high output because its emission spectrum can extend toward the visible range.

A 940 nm LED is much harder for humans to see.

850 nm vs. 940 nm IR LED

These are two of the most common IR LED wavelengths.

850 nm IR LED

850 nm typically offers strong compatibility with silicon camera sensors.

It is widely used for:

• CCTV night vision

• Security cameras

• Machine vision

• IR illuminators

• Sensors

• Some photobiomodulation devices

Its disadvantage is that the LED may show a faint red glow.

940 nm IR LED

940 nm is commonly selected when low visibility to humans is more important.

Typical applications include:

• TV remote controls

• IR data transmission

• Proximity sensors

• Invisible night illumination

• Security devices

Many silicon image sensors have lower sensitivity at 940 nm than around 850 nm, so more optical power may be required for equivalent camera illumination depending on the sensor.

How Does an IR Remote Control Work?

A TV remote provides a simple example.

When you press a button:

Button → Electronic circuit → IR LED → Pulsed 940 nm signal → TV IR receiver

The IR LED does not simply stay continuously illuminated. It is rapidly modulated according to an encoded signal.

The receiver detects these pulses and interprets the command.

This allows commands such as:

Power / Volume / Channel / Menu

to be transmitted wirelessly.

How Do IR LEDs Work in Night-Vision Cameras?

At night, IR LEDs illuminate an area with radiation that humans cannot readily see.

The process is:

IR LED → IR light hits object → object reflects IR → camera sensor detects reflection → image is produced

This allows a camera to capture scenes even when there is little or no visible illumination.

What Materials Are Used for IR LEDs?

IR LEDs commonly use III-V semiconductor materials such as GaAs (gallium arsenide) and AlGaAs (aluminum gallium arsenide), among other compound-semiconductor structures.

Changing the semiconductor composition changes the bandgap, which changes the emitted wavelength.

This is why manufacturers can produce LEDs centered at wavelengths such as:

730 / 810 / 850 / 940 nm

and other specialized wavelengths.

IR LED Forward Voltage

Infrared LEDs often have a lower forward voltage than blue or white LEDs.

For example, an IR LED might operate at roughly:

Vf ≈ 1.2–1.8 V

depending on wavelength, current, junction temperature and semiconductor structure.

By comparison, a white LED commonly operates around:

Vf ≈ 2.7–3.4 V

Always use the actual LED datasheet because these ranges are only representative.

How Do You Know an IR LED Is Working?

Because IR radiation is invisible, looking at the LED isn't a reliable test.

A basic method is to use a camera that is sensitive to the LED's wavelength.

For example, point a compatible phone camera at a TV remote and press a button. Some cameras can display the IR LED as a flashing white or purple light.

However, many modern phones include strong IR-blocking filters, so failure to see the LED does not necessarily mean it is defective.

For professional testing, use:

• Photodiode

• Optical power meter

• Spectrometer

• IR-sensitive camera

• Integrating sphere

What Is Radiant Power?

For visible white LEDs, specifications such as lumens (lm) are important because lumens are weighted according to human visual sensitivity.

For IR LEDs, lumens are generally inappropriate because the radiation isn't intended for human vision.

Instead, IR LED specifications commonly include:

Radiant flux (mW) — total optical output

Radiant intensity (mW/sr) — directional optical intensity

Peak wavelength (nm) — wavelength of maximum spectral output

Viewing angle (°) — beam spread

These are important parameters when selecting IR LEDs for cameras, sensors and other systems.

SMD IR LED Packages

Infrared LEDs can be manufactured in many SMD formats.

For example:

2835 IR LED — compact arrays and lower/mid-power applications

3030 IR LED — higher-output applications

3535 IR LED — high-power IR illumination and specialized equipment

5050 IR LED — larger or multi-die configurations

The package number describes the approximate package dimensions—not the wavelength.

Therefore:

3535 ≠ 850 nm

A 3535 package could contain an 850 nm, 940 nm or another wavelength depending on the semiconductor die inside.

IR LED vs. Visible LED

The basic operating principle is essentially the same.

Visible LED: electrical energy → visible photons

IR LED: electrical energy → infrared photons

The main difference is the semiconductor bandgap and resulting photon wavelength.

Applications of IR LEDs

IR LEDs are widely used in:

Security: CCTV and night vision

Consumer electronics: remote controls

Automotive: sensing and driver-monitoring systems

Industrial: machine vision and photoelectric sensors

Medical/wellness equipment: selected near-IR photobiomodulation systems

Biometrics: facial and iris sensing

Smart devices: proximity and gesture detection

An IR LED works through electroluminescence. Electrical current causes electrons and holes to recombine inside a semiconductor, releasing energy as infrared photons.

The key concept is:

Electricity → P-N Junction → Electron-Hole Recombination → Infrared Light

Among common products, 850 nm is particularly popular for night vision and IR illumination, while 940 nm is widely used for remote controls and applications requiring less visible red glow.

For B2B selection of 2835, 3030, 3535 or 5050 IR LEDs, the most important specifications include wavelength, radiant flux, radiant intensity, forward current, forward voltage, viewing angle and thermal performance.