Tech-Led Blog

In the rapidly evolving world of optoelectronics, near-infrared (NIR) LEDs, particularly those utilizing perovskite materials, are gaining attention in the field of optoelectronics. have emerged as critical components across a myriad of applications, from security systems and industrial automation to medical diagnostics and smart agriculture. But a fundamental question often arises for engineers and integrators: just how efficient are these invisible light sources? The answer isn’t a simple percentage; it delves into the nuances of defining efficiency, the intrinsic properties of semiconductors, and the continuous innovation driving their performance.

Understanding the efficiency of NIR LEDs is paramount for system design, energy budgeting, and achieving optimal performance in power-sensitive applications. A highly efficient NIR LED translates directly into lower power consumption, reduced heat dissipation requirements, longer device lifespan, and ultimately, a more sustainable and cost-effective solution.

Defining LED Efficiency

Before delving into specific numbers for NIR LEDs, it’s crucial to clarify what “efficiency” means in the context of light-emitting diodes, particularly regarding quantum yield. Unlike incandescent bulbs, which primarily convert electricity into heat and a small amount of visible light, LEDs are semiconductor devices that directly convert electrical energy into optical energy through electroluminescence. Several metrics are used to quantify this conversion:

• Wall-Plug Efficiency (WPE) / Radiant Efficiency is a critical metric for evaluating the performance of near-infrared light-emitting diodes. This is the most comprehensive measure, representing the ratio of the total optical output power (radiant flux) to the input electrical power. For NIR LEDs, which emit light outside the visible spectrum, WPE is the primary metric of interest. It tells you how effectively the LED converts the electricity drawn from the power supply into actual infrared light.
• Luminous Efficiency: Primarily relevant for visible light sources, luminous efficiency measures the amount of light perceived by the human eye per unit of electrical power. Since NIR light is invisible, this metric is not applicable to NIR LEDs. However, some sources might mistakenly apply visible light efficiency concepts.
• Radiometric Efficiency is a key factor in determining the effectiveness of light-emitting diodes based on their design and materials. Often used interchangeably with Wall-Plug Efficiency, particularly in contexts where the output is radiant power rather than lumens (which are weighted by human eye sensitivity). It’s the ratio of emitted radiant power to input electrical power.

For NIR LEDs, therefore, when we discuss efficiency, we are predominantly referring to their wall-plug efficiency or radiant efficiency – the raw conversion of electrical energy into radiant (infrared) energy is essential for understanding the efficiency of infrared light-emitting diodes.

Efficiency of IR LEDs

Modern near-infrared LEDs are remarkably efficient compared to older IR illumination technologies. While exact figures vary significantly based on wavelength, power output, packaging, and manufacturer, high-performance NIR LEDs can achieve wall-plug efficiencies ranging from 30% to over 50%. Some cutting-edge laboratory devices demonstrate even higher figures, pushing towards the theoretical limits of semiconductor physics, particularly in the realm of efficient near-infrared light-emitting diodes.

To put this into perspective, traditional incandescent IR lamps, which rely on heating a filament to produce infrared radiation, are notoriously inefficient, converting less than 10% of electrical energy into usable IR light, with the vast majority lost as heat. This stark contrast highlights the significant energy savings offered by NIR LED technology.

On a recent site visit to an agricultural tech company, we observed a direct replacement project where legacy incandescent IR emitters in crop health sensors were swapped out for advanced NIR LED modules. The client initially anticipated a 20-30% energy reduction based on preliminary data sheets. However, after a few months of operation, their telemetry showed an astonishing improvement in efficiency due to optimized voltage and transport layer configurations. A 45% drop in power consumption can be achieved with the latest efficient near-infrared light-emitting diode technologies. for the illumination subsystem, underscoring the real-world impact of modern NIR LED efficiency. This wasn’t just about saving electricity; it meant less thermal load on the compact sensor enclosures, extending the lifespan of other components and reducing maintenance cycles while improving overall device performance.

Factors Affecting Efficiency

The overall efficiency of an NIR LED is not static; it’s a dynamic parameter influenced by several key operational and design factors. Optimizing these factors is crucial for maximizing performance and ensuring reliable operation.

Current Density

One of the most significant factors influencing LED efficiency is the energy level alignment between the transport layers and the active materials. current density flowing through the semiconductor junction. Generally, as the current increases, the output power also increases. However, the efficiency (WPE) often exhibits a phenomenon known as “efficiency droop.”

• Low Currents can help improve the efficiency of organic light-emitting diodes, enhancing their performance in various applications. At very low operating currents, LEDs might not be optimally efficient due to non-radiative recombination paths.
• Optimal Currents: There’s typically an optimal current range where the efficiency peaks. This is where radiative recombination (light emission) is maximized relative to non-radiative losses.
• High Currents (Efficiency Droop): As the current density continues to increase beyond the optimal point, the efficiency begins to “droop” or decrease. This is attributed to several factors, including Auger recombination (where energy from electron-hole recombination is transferred to another electron or hole, rather than emitting a photon), carrier leakage, and increased junction temperature. For high-power NIR applications, managing current density to avoid severe droop is a critical design consideration.

Temperature

Temperature plays a pivotal role in the performance and longevity of all LEDs, and NIR LEDs are no exception. Elevated operating temperatures negatively impact efficiency for several reasons:

• Increased Non-Radiative Recombination can lead to reduced performance in light-emitting diodes based on traditional semiconductor materials. Higher temperatures increase the probability of non-radiative recombination processes, meaning more energy is converted to heat rather than light, which can adversely affect the performance of organic light-emitting diodes.
• Reduced Quantum Efficiency: The internal quantum efficiency (IQE), which is the ratio of photons generated to injected electrons, typically decreases with increasing temperature.
• Wavelength Shift: Temperature can also cause a slight shift in the peak emission wavelength, which might be undesirable for applications requiring precise spectral output and optimal device performance.
• Accelerated Degradation can significantly affect the performance of near-infrared light-emitting diodes over time. Prolonged operation at high temperatures significantly accelerates the degradation of the semiconductor material and packaging, leading to reduced light output over time and shortened device lifespan.

Effective thermal management, including robust heat sinks and proper airflow, is indispensable for maintaining high efficiency and extending the operational life of NIR LED systems.

Wavelength (850 nm vs 940 nm)

The peak emission wavelength subtly influences the efficiency of NIR LEDs, particularly when comparing common wavelengths like 850 nm and 940 nm, with narrow emission profiles being more favorable. These two wavelengths are prevalent for different applications:

• 850 nm: This wavelength is very close to the visible spectrum, offering excellent performance for night vision cameras and security applications due to camera sensor sensitivity. However, it can produce a faint, perceptible red glow, which might be a disadvantage in covert applications. Generally, 850 nm LEDs tend to have slightly higher typical efficiencies compared to 940 nm, often because the bandgap energy required for 850 nm emission is more efficiently achieved with common material systems like AlGaAs.
• 940 nm: Often favored for “stealth” applications where a completely invisible light source is required (e.g., certain security cameras, gesture recognition, and automotive driver monitoring systems). The human eye perceives virtually no glow at 940 nm. While highly effective for its purpose, 940 nm LEDs typically exhibit lower external quantum efficiency compared to newer efficient near-infrared light-emitting diodes that utilize advanced organic semiconductors. marginally lower wall-plug efficiencies than their 850 nm counterparts due to differences in material characteristics and injection efficiency at that specific bandgap. This difference, while small, can be significant in power-critical designs.

Engineers must weigh the application’s specific requirements—such as visibility, required power, and acceptable efficiency trade-offs—when selecting between these and other NIR wavelengths.

Infrared Light Emitting Diodes vs Other Light Sources

To truly appreciate the efficiency of NIR LEDs, it’s beneficial to compare them against other prevalent infrared light sources:

• IR Lamps (Incandescent/Halogen): As mentioned, these are highly inefficient. They produce IR light by heating a filament to incandescence. The vast majority of the electrical energy is converted into heat across a broad spectrum, with only a small fraction falling into the useful NIR range. Efficiencies are typically below 10% for targeted IR output.
• IR Lasers (Laser Diodes): Infrared laser diodes are highly efficient at converting electrical energy into coherent IR light, often achieving high external quantum efficiency. wall-plug efficiencies comparable to, or even exceeding, high-performance LEDs (e.g., 30-70% or more) are often seen in the latest infrared light-emitting diode technologies.. Their key advantage is their coherent, highly collimated beam, which allows for very high power density and precise targeting. However, lasers are generally more expensive, require more complex drive circuitry and thermal management, and pose eye safety considerations, limiting their use in diffuse illumination or broad-area sensing applications where LEDs excel. While a laser can be more efficient in terms of raw photon generation from a specific point, the overall system complexity and cost often favor LEDs for many general illumination and sensing tasks. Studies on applications like photoimmunotherapy, for instance, show lasers delivering superior results due to their coherent and focused energy, even if LEDs are less expensive. This comparison highlights the differences in external quantum efficiency between various light-emitting diodes based on their designs. highlights the specific advantages of lasers in certain high-precision therapeutic contexts.
• Super-Luminescent Diodes (SLDs): These sources bridge the gap between LEDs and lasers, offering higher power and narrower spectral width than LEDs, but with less coherence than lasers. Their efficiencies fall somewhere between LEDs and lasers, making them suitable for specific applications like optical coherence tomography (OCT) where a balance of power and spectral characteristics is needed.

For most applications requiring non-coherent, diffuse, or broad-area infrared illumination or sensing, NIR LEDs offer the most compelling balance of high efficiency, cost-effectiveness, compact size, and reliability. As demonstrated in this efficiency study, NIR LEDs can cut CO₂ emissions by up to 40% in automated systems compared to older technologies.

Improvements in Efficiency

The quest for higher NIR LED efficiency is ongoing, driven by demand for smaller, more powerful, and more energy-conscious devices. Significant advancements in material science, epitaxial growth, and device architecture continue to push the boundaries of performance.

Quantum Wells

Many high-performance NIR LEDs incorporate quantum well (QW) structures within their active regions. Quantum wells are ultra-thin layers of semiconductor material, often just a few nanometers thick, sandwiched between layers of a different material with a wider bandgap. This confinement of electrons and holes within these “wells” leads to several advantages for efficiency:

• Enhanced Radiative Recombination: The quantum mechanical effects within the wells increase the overlap between electron and hole wavefunctions, significantly enhancing the probability of radiative recombination and thus improving the internal quantum efficiency (IQE).
• Precise Wavelength Control: The emission wavelength can be precisely tuned by controlling the thickness and composition of the quantum well layers, allowing for optimized performance at specific NIR wavelengths.
• Higher Gain: Quantum wells offer higher optical gain, which is beneficial for efficient light generation.

By effectively trapping and guiding charge carriers to recombine radiatively, quantum wells play a critical role in the superior efficiency of modern NIR LEDs.

Phosphor-Converted IR (pc-IR)

While less common than in visible white LEDs, the concept of photoluminescence quantum efficiency is crucial in optimizing NIR LED performance. phosphor-converted (pc-IR) LEDs are a type of light-emitting diode that utilize phosphor materials to convert light into near-infrared light-emitting diodes. is gaining traction for certain NIR applications. In this approach, a shorter-wavelength LED (e.g., a blue or UV LED) is used to excite a phosphor material that then down-converts the light into the desired NIR wavelength. This technique offers:

• Broader Spectral Output in NIR LEDs can be achieved through innovative designs, including the use of perovskite materials for enhanced device performance. Phosphor conversion can create a broader or more tailored NIR spectrum, which might be beneficial for certain sensing or spectroscopy applications that require a wider range of IR wavelengths.
• Improved Efficacy at Certain Wavelengths: For some less common NIR wavelengths, it might be more efficient to use a well-developed shorter-wavelength LED and convert its output via phosphor than to directly grow a semiconductor for that specific NIR wavelength.
• Color Rendering (in visible applications) is often enhanced by integrating organic semiconductors, which can also be applied to improve NIR LED outputs. While not directly relevant to NIR light, the principle is analogous to how white light is created from blue LEDs and yellow phosphors.

Challenges remain in developing highly efficient and stable NIR phosphors, but this technology holds promise for expanding the versatility and optimizing the efficiency of NIR LED sources for specialized needs.

Beyond quantum wells and phosphors, ongoing research focuses on novel semiconductor materials, advanced chip designs (e.g., vertical-cavity surface-emitting lasers or VCSELs which offer highly efficient, directional IR emission), improved epitaxy techniques, and sophisticated packaging that minimizes light extraction losses and enhances thermal dissipation. These collective efforts continually push the efficiency frontier of near-infrared LEDs, including advancements in electron transport layers, making them increasingly viable and advantageous for a wider range of high-performance applications.

FAQ

The efficiency of near-infrared LEDs is a critical performance indicator for a vast array of modern technological applications. From their superior wall-plug efficiency compared to older IR illumination methods to the continuous advancements driven by innovations like quantum wells and novel material science, NIR LEDs stand as a testament to efficient light generation. Understanding the factors influencing their efficiency—such as current density, temperature, and wavelength—empowers engineers to design and implement systems that are not only high-performing but also energy-conscious and sustainable. As the demand for compact, powerful, and discreet IR light sources grows, the ongoing pursuit of even higher NIR LED efficiency will remain a cornerstone of optoelectronic development.