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On a recent site visit to a high-tech security installation, I noticed a bank of LEDs glowing bright red on one panel, while a nearby infrared camera’s LED illuminators glowed completely unseen by my eyes. This simple scene highlights the fundamental difference: normal LEDs emit light in the visible range (so we can see them), whereas infrared (IR) LEDs emit longer-wavelength light beyond human vision.
Emission Wavelength (Visible vs Infrared)
Normal LEDs emit light in the visible spectrum (roughly 380–750 nm), making colors like red, green, blue, and white. The human eye is sensitive to about 380–750 nm. In contrast, IR LEDs emit light with wavelengths typically above 700 nm. For example, near-infrared LEDs commonly emit around 800–940 nm – wavelengths our eyes cannot see. This means an IR LED might be on and bright to a camera sensor, but to us it appears dark. The figure below illustrates the visible band versus the infrared band.
Visible light vs infrared: Visible LEDs produce photons we perceive as colors, whereas IR LEDs produce photons in the invisible infrared range. In practice, manufacturers classify IR LEDs into sub-bands (near-IR ~700–1000 nm, short-wave IR, etc.), but the key is that IR LEDs lie just beyond the visible range. For context, Wikipedia notes that the human eye responds to about 380–750 nm, so IR LEDs emit beyond that range.
Materials & Construction (GaP/GaN vs GaAs and Packaging)
LED chip materials: The color (or wavelength) of an LED depends on its semiconductor bandgap. Normal visible LEDs often use materials like gallium arsenide phosphide (GaAsP), gallium phosphide (GaP), or gallium nitride (GaN) to cover red, green, blue and white light. For example, red and green LEDs commonly use GaAsP or GaP alloys, and modern blue LEDs use GaN. In contrast, infrared LEDs typically use gallium arsenide (GaAs) or related alloys (like aluminum-gallium-arsenide, AlGaAs) tuned for IR output.
Packaging differences: Physically, IR LEDs often look similar to visible LEDs (they may have a clear or tinted epoxy lens), but there are differences. High-power IR LEDs sometimes use a dark lens or black epoxy to filter out any stray visible light, resulting in a “black” LED that hides the die. In single LEDs (like 5mm IR diodes) the epoxy might be deep red or opaque. By contrast, normal LEDs often have colored bodies or clear domes shaped for lighting. Package form factors (DIP vs SMD vs COB) exist for both types, but IR LEDs for illumination or sensing often come in arrays and specially coated packages to focus infrared output.
Electrical Characteristics
One clear difference is forward voltage. Because infrared photons have lower energy, IR LEDs require a smaller bandgap, so they conduct at lower voltages. For example, Tech-LED notes that IR LEDs have a forward voltage around 1.2–1.5 V, whereas many visible LEDs need ~2–3 V to conduct. In fact, an electronics reference states IR LEDs typically turn on at ~1.5–1.7 V, while a blue LED might need ~3.3 V.
- Forward voltage: Visible LEDs (red/green) ~2.0 V, blue ~3.3 V; IR LEDs ~1.2–1.7 V.
- Current: Both types may run similar currents (e.g. 20 mA for indicator LEDs, hundreds of mA for high-power LEDs), but IR LED datasheets often specify radiant intensity instead of luminous intensity.
- Output units: Visible LEDs are rated in lumens or candela (light output to human eye), whereas IR LEDs are rated in milliwatts (optical power) or radiant intensity (mW/sr) since output is invisible.
Applications (Lighting/Indicators vs Sensing/Communication)
Visible LEDs and IR LEDs serve very different applications. Normal LEDs are used where human-visible illumination or indication is needed: indicator lights, digital displays, color lighting, architectural and general illumination, backlights, etc. Wikipedia explains that LEDs are “widely used in indicator and display functions” and white LEDs are replacing other light sources for general lighting. On the other hand, IR LEDs are used for non-visual signaling and sensing:
- Remote controls & data transfer: TV or AC remotes use ~940 nm IR LEDs to send commands to devices. IR LEDs also enabled wireless IrDA data links and are used in some short-range wireless modules [oai_citation:13‡moon-leds.com.
- Security/night vision: IR LED illuminators flood a scene with invisible light for cameras. An IR camera in a security system or wildlife cam can see in total darkness by using IR LEDs (850/940 nm) that are imperceptible to people [oai_citation:14‡tech-led.com](https://tech-led.com/near-infrared-nir-led/#:~:text=,21). This provides covert illumination.
- Sensors and proximity: Many sensors use IR LEDs. For example, proximity sensors on phones, obstacle detectors, and automatic faucets emit IR light and detect reflections. Automatic garage door and break-beam alarms also use IR emitters and detectors.
- Medical/biometric: IR LEDs penetrate skin and are used in pulse oximeters (measuring blood oxygen), pulse sensors, and vein finders. They’re also used in various non-contact medical instruments and IR-based biometric devices (like some facial recognition systems using 850 nm flood illumination).
- Machine vision and optical comm: In industry, IR LEDs illuminate products for machine vision (sometimes using 880 nm or 940 nm to see through certain materials). In fiber optics, certain wavelengths around 850–1550 nm are used to transmit data (IR LEDs in multimode fiber).
In summary, normal LEDs provide visible light for human use (lighting, signage, indicators), whereas IR LEDs provide invisible light for devices and sensors. In fact, Tech-LED’s near-infrared LED guide emphasizes this point: a normal LED “lights up” for people, while an IR LED is used for communication or illumination that only electronic sensors detect.
Detection by Humans vs Devices
The most obvious difference is how each is perceived. You can look at a normal LED and see its light and color. By contrast, when an IR LED is on, your eyes see nothing – it looks off. This is because IR light is invisible to our eyes. To detect an IR LED, you need a camera or an IR photodiode. For example, a smartphone camera will often show a faint glow if you point it at an active remote-control LED. Tech-LED notes: “you cannot tell if an IR LED is on just by looking (since it doesn’t visibly glow), whereas a normal LED obviously lights up when active”. In practice, engineers use IR-sensitive cameras, IR viewers, or photodiodes to see IR illumination.
Perception: In visible LEDs, the output is designed for human perception (color and brightness). In IR LEDs, the output is for machines – a camera sensor or detector picks up the IR. This is why IR LEDs are popular in night-vision cameras and remote controls: they are “invisible” to intruders or users, but clear to electronic sensors.
FAQ
Q: Can I see infrared LED light without a camera?
A: No. Infrared light is beyond the human visible range. An IR LED glowing will appear dark to your eyes, although some IR LEDs (especially 850 nm) may emit a faint red glow in the visible band. To verify an IR LED is on, use an IR-sensitive camera or an IR photodiode.
Q: Why do IR LEDs have a lower forward voltage than visible LEDs?
A: The forward voltage of an LED is set by its semiconductor bandgap. IR LEDs use materials with smaller bandgaps (e.g. GaAs), so they conduct and emit at ~1.2–1.7 V. Visible LEDs (green, blue, UV) have larger bandgaps (GaN, etc.) requiring 2–3+ V.
Q: What materials are used in IR LEDs vs normal LEDs?
A: Normal visible LEDs typically use materials like GaAsP/GaP for reds/greens and GaN for blues. In contrast, IR LEDs use GaAs or AlGaAs-based chips specifically engineered for IR emission. These different materials tune the emitted wavelength.
Q: How do I distinguish an IR LED from a regular LED?
A: IR LEDs often look similar to regular LEDs but may have a black, deep red, or opaque lens. You won’t see it glow when on. To test one, point a digital camera at the LED while powering it; the camera will usually show a purplish light if it’s an IR LED.
Q: What are common uses for IR LEDs that normal LEDs can’t do?
A: IR LEDs are used in applications where human vision isn’t needed or would be intrusive – remote controls, surveillance cameras, IR communication links, proximity sensors, medical sensing, etc. They allow devices to “see” or communicate without visible light.
What is the difference between an IR sensor and an IR LED?
An IR sensor detects infrared radiation while an IR LED (light-emitting diode) emits infrared light. The IR sensor is designed to respond to infrared light signals, which are invisible to the human eye, whereas the IR LED serves as a source, producing light within the infrared spectrum, typically around 850nm IR.
How do IR receivers work with IR LEDs?
IR receivers are devices that detect and interpret signals emitted by IR LEDs. When an IR LED emits infrared light, the IR receiver can capture this light if it falls within its sensitivity range, allowing it to process the information, such as in remote controls or various applications of IR technology.
What are the applications of IR sensors and IR LEDs?
IR sensors and IR LEDs have numerous applications, including remote controls, motion detectors, and data transmission. They are commonly used in security systems, TVs, and other consumer electronics, as well as in industrial settings for various sensing applications.
What is the difference between different types of IR LEDs?
The differences between types of IR LEDs generally relate to their wavelength, power output, and design. For instance, high power LEDs emit stronger infrared light, while standard IR LEDs may be used for basic remote control functions. Each type serves specific needs based on the application, such as whether the light is for short-range or long-range detection.
How does an IR transmitter LED differ from a standard LED?
An IR transmitter LED is specifically designed to emit infrared light, which is not visible to the human eye, while a standard LED emits visible light. The IR transmitter LED is optimized to generate light at specific wavelengths suitable for applications like remote signaling, whereas standard LEDs are used for general illumination.
Can IR sensors detect ambient light?
Most IR sensors are designed to detect infrared light rather than visible ambient light. However, some advanced models can differentiate between IR signals and ambient light, allowing them to function accurately in varying lighting conditions. This capability is crucial in applications where infrared signals might be affected by external light sources.
What is the difference in light emission between IR LEDs and visible light LEDs?
The primary difference in light emission is that IR LEDs emit infrared light, which is not visible to the human eye, while visible light LEDs emit light that can be seen. The light emitted by IR LEDs often serves purposes such as communication or detection, whereas visible light LEDs are used for general lighting and display purposes.
Ready to explore LEDs for your project? Contact the Tech-LED team for expert advice and custom solutions. Contact Tech-LED.
