Infrared LEDs: a complete guide

What are infrared LEDs: definition and fundamental characteristics

An infrared LED (IR LED) is a light-emitting diode that, when forward-biased, emits photons with wavelengths in the infrared range. Infrared radiation—discovered by William Herschel in 1800—is a form of radiant energy invisible to the human eye but perceptible as heat. IR LEDs represent the solid-state, high-efficiency counterpart to traditional infrared light sources, such as incandescent lamps with filters, offering decisive advantages in longevity, compactness, switching speed, and energy consumption.

The principle behind infrared emission

The operation of an infrared LED is based on the same physical principle as visible LEDs: electroluminescence in a p-n semiconductor junction. When a forward voltage is applied across the junction, electrons from the n-region recombine with holes in the p-region, releasing energy in the form of photons. The energy (and thus the wavelength) of the emitted photon is determined by the semiconductor’s bandgap.

To produce infrared radiation, materials with a narrower bandgap than those used for visible light are selected. For example, gallium arsenide (GaAs), with a bandgap of approximately 1.43 eV, emits light in the near-infrared (NIR) around 870 nm. By varying the semiconductor composition (e.g., using GaAlAs or InGaAs), the emission wavelength can be precisely tuned to cover different sub-bands of the IR spectrum according to application needs.

Semiconductor materials for infrared LEDs: brief overview

The choice of semiconductor material is the primary factor determining the characteristics of infrared LEDs. In addition to GaAs—used for emissions between 750 and 950 nm—gallium phosphide (GaP) doped with zinc-oxygen enables LEDs with a peak emission at 700 nm, right at the boundary between visible red and IR.

For applications requiring longer wavelengths in the mid-infrared, indium gallium arsenide (InGaAs) is used. In the far-infrared range—where emission is essentially thermal radiation—quantum cascade LEDs (QCLs) based on complex heterostructures are employed, although this technology differs significantly from conventional LEDs. The table below summarizes the most common materials and their typical emission ranges:

The design of an infrared LED involves more than just selecting the active material. The chip geometry, electrode layout for uniform current distribution, inclusion of reflective layers to maximize light extraction, and the package type (epoxy, silicone, or ceramic) are all critical factors affecting external quantum efficiency, emission angle, thermal stability, and long-term reliability. IR LED packages are often black or dark blue to minimize reflection of ambient visible light and may include lenses to focus the beam.

How infrared LEDs work: from theory to circuit

Key electrical and optical parameters

To properly select and use an infrared LED, one must understand and interpret the following fundamental parameters, typically specified in the manufacturer's datasheet:

• Forward voltage (V_F): the voltage drop across the LED at nominal operating current. For GaAs-based IR LEDs, V_F typically ranges from 1.2 V to 1.6 V—slightly lower than visible LEDs due to the smaller bandgap.
• Forward current (I_F): the recommended operating current, which may range from a few mA for sensing applications to hundreds of mA for high-power IR LEDs used in illumination. Exceeding it significantly drastically reduces lifetime.
• Peak current (I_FP): for infrared LEDs used in pulsed applications (e.g., remote controls), this is the maximum permissible current for short durations (on the order of microseconds). It can be much higher than I_F, enabling very intense light pulses.
• Optical output power (P_o): total radiant flux emitted, measured in watts (W) or milliwatts (mW). A standard LED may emit tens of mW; high-power modules can exceed 1 W.
• Peak wavelength (λ_p): the wavelength at which emission is maximum. It is chosen based on the sensitivity of the receiving detector (photodiode or phototransistor).
• Spectral bandwidth at half-maximum (Δλ): the width of the emission spectrum measured at half the peak power. IR LEDs typically have a Δλ of 20–50 nm—much broader than lasers—making them less suitable for applications requiring extreme monochromaticity.
• Viewing angle (θ_1/2): the angle within which radiant intensity drops to 50% of its on-axis maximum. It can be very narrow (10°–20°) with collimating lenses or very wide (120°–150°) for diffuse illumination.

Driving circuits: basic schematic

The simplest circuit to drive infrared LEDs consists of a current-limiting resistor in series, powered by a supply voltage (V_CC). The resistor value R_s is calculated using Ohm’s law: R_s = (V_CC – V_F) / I_F. For example, with a 5V supply, an IR LED with V_F = 1.4V and I_F = 100mA, R_s = (5 – 1.4) / 0.1 = 36 Ω. This resistor must also be rated for power dissipation: P = (V_CC – V_F) × I_F = 0.36W in this case, so a resistor rated for at least 0.5W is required.

For applications requiring higher current stability (e.g., to avoid intensity variations with temperature or to drive LED arrays in series), constant-current drivers are preferred. These can be implemented with dedicated current regulators, transistor-based current sources, or integrated LED driver ICs. For infrared LEDs used in high-speed pulsed mode (e.g., IR data communication), the driver circuit must switch current rapidly, often using fast MOSFET transistors.

Fundamental differences between infrared LEDs and conventional LEDs

Materials, efficiency, and performance measurement

The most obvious difference lies in the active semiconductor material. While white illumination LEDs typically use nitrides (InGaN) for blue/UV emission combined with phosphors for wavelength conversion, IR LEDs use arsenides or phosphides, as previously discussed. This affects both threshold voltage (lower for IR) and efficiency.

Efficiency is measured differently depending on whether the LED is visible or infrared. For visible LEDs, performance focuses on human visual perception, measured in lumens (lm) and luminous efficacy (lm/W), weighted by the human photopic sensitivity curve V(λ). For infrared LEDs, since emission is invisible, the relevant metric is radiant efficiency, expressed as the ratio of total optical output power (in watts) to electrical input power (W/W or often mW/mA). IR LEDs can achieve very high radiant efficiencies—often exceeding 40–50%—since they avoid the inherent inefficiency of phosphor-based down-conversion used in white LEDs.

The following table compares key characteristics:

Ocular safety considerations

A critical and often overlooked aspect concerns eye safety. Infrared radiation is invisible and thus does not trigger the blink reflex that protects the eye from intense visible light. Moreover, the cornea and lens are transparent to near-infrared radiation, allowing it to reach—and potentially damage—the retina, just like visible light.

Therefore, for high-power infrared LEDs, compliance with safety standards (such as IEC 62471) defining exposure limits is essential. Often, these LEDs are classified as "Class 1" (safe under all reasonably foreseeable conditions) only when incorporated into a product that limits direct exposure or emitted power. Designing with IR LEDs thus requires special attention to the risks associated with the invisibility of their emitted radiation.

Applications of infrared LEDs

Security and surveillance: invisible night illumination

One of the most common and recognizable uses of infrared LEDs is in auxiliary illumination for security (CCTV) cameras and video doorbells. Standard CCD and CMOS cameras are sensitive not only to visible light but also to near-infrared (NIR), typically up to about 1000–1100 nm. By installing an array of high-power infrared LEDs (often at 850 nm or 940 nm) around the camera lens, the scene can be illuminated at night without producing any visible glow, enabling discreet and continuous surveillance.

The choice between 850 nm and 940 nm involves a trade-off. 850 nm IR LEDs offer superior performance: camera sensors are generally more sensitive at this wavelength, and the emitted light—though almost entirely invisible—shows a faint deep-red glow when viewed up close, which can be useful for verifying operation.

940 nm IR LEDs are completely invisible (no glow), maximizing discretion, but require high-quality camera sensors to achieve the same illumination performance, as silicon sensitivity drops significantly beyond 900 nm. Required power depends on illumination distance; large areas (yards, parking lots) use external IR illuminators with collimated beams and output powers reaching several watts.

Automation, remote controls, and optical communication

This is the domain where infrared LEDs first gained mass adoption: the remote control. Nearly every TV, air conditioner, or audio system remote uses an IR LED (typically at 940 nm) to transmit commands via a digital modulation protocol. Advantages include extremely low cost, immunity to electromagnetic interference, and directionality (the signal doesn’t pass through walls, avoiding cross-room interference).

Beyond consumer remotes, IR LEDs are used in industrial automation and proximity sensors. IR LED–phototransistor pairs can detect object presence/absence (beam-break sensors), measure distance (via triangulation or time-of-flight), or read barcodes. In industry, these sensors are preferred in dusty environments or where magnetic sensors might be affected by electromagnetic fields. For short-range data communication (IrDA)—though largely supplanted by Bluetooth—IR LEDs still offer a secure, low-latency channel for file exchange between devices.

How an infrared remote control works

The system’s core is the infrared LED, driven by an encoder IC. When a button is pressed, the IC generates a digital pulse train specific to that command (common protocols include RC-5, NEC, SIRC). This signal modulates the current through the IR LED, turning it on and off at typical carrier frequencies like 38 kHz or 56 kHz. Carrier modulation is essential for two reasons: it increases radiant efficiency (by transmitting high-power peak pulses) and allows the receiver (a photodiode tuned to the same frequency) to filter out constant ambient light (noise) and recognize only the modulated signal. This simple yet effective principle has made IR technology the de facto standard for remote control for decades.

Biomedical and analytical applications

In medical and analytical fields, infrared LEDs are valuable tools for non-invasive diagnostics. Near-infrared light (often called the "therapeutic window," 650–1350 nm) penetrates biological tissues more deeply than visible light because it is less absorbed by hemoglobin and water. This enables techniques like near-infrared spectroscopy (NIRS), where arrays of IR LEDs at multiple wavelengths illuminate tissue (e.g., brain or muscle), and a detector analyzes reflected or transmitted light to infer parameters like blood oxygenation (oximetry), tissue metabolism, or chemical composition.

Other applications include fingertip pulse oximeters, which use red and infrared LED pairs to measure blood oxygen saturation (SpO₂), and phototherapy devices, where IR light stimulates circulation, reduces inflammation, or accelerates wound healing. In laboratories, temperature-stabilized IR LEDs serve as compact, cost-effective light sources for spectrophotometers and composition analyzers.

Poultry farming and livestock

In the poultry sector, infrared LEDs offer innovative solutions for animal welfare and sustainability. Primarily used as radiant panels, they provide direct, localized heating for chicks and young animals, with up to 60% higher energy efficiency than traditional systems. IR light can also help reduce problematic behaviors—such as feather pecking in laying hens—by creating a calmer environment. IR illumination also enables continuous animal monitoring via IR cameras without disrupting natural day-night cycles, supporting more precise and ethical farming practices.

IR Spectra Used in Poultry Farming: Poultry applications leverage two main infrared bands. For radiant heating, 850 nm and 940 nm LEDs are predominantly used, with a preference for 940 nm when complete invisibility is required. For deep tissue warming—especially in chicks—spectra around 980 nm are particularly effective, as water in biological tissues strongly absorbs this wavelength, ensuring optimal conversion of light energy into heat.

Infrared LEDs: a world in continuous evolution

In this technologically advanced landscape, choosing the right optoelectronic component supplier is crucial. Support in selecting the right wavelength, designing optimal driving circuits, and providing mechanical and thermal integration guidance ensures every installation achieves maximum performance and reliability.

Whether you're designing a new video surveillance system, an innovative medical device, or an industrial automation line, a deep understanding of the capabilities and technical specifications of infrared LEDs is the first step toward success. This guide has aimed to provide a solid foundation for that understanding, in the belief that the invisible light of infrared will continue illuminating the path of technological progress across countless sectors.