LED

A light-emitting diode (LED) is a semiconductor device that emits light when an electric current passes through it. It is a p-n junction diode in which charge carriers, electrons and holes, recombine across the junction and release energy as photons, a process called electroluminescence. The color of the emitted light is set by the band gap of the semiconductor material rather than by a filter or a phosphor, so different alloys produce different wavelengths from the infrared through the visible spectrum to the ultraviolet.

The first practical visible-spectrum LED was demonstrated by Nick Holonyak Jr. at General Electric in 1962. Since then the LED has become one of the building blocks of display and sensing hardware. In virtual reality (VR) and augmented reality (AR) the LED appears in several distinct roles: as the light source behind liquid-crystal panels (LED and Mini-LED backlights), as the light-emitting element of self-emissive displays (OLED, Micro-OLED and inorganic Micro-LED microdisplays), and as the infrared emitter used for positional tracking, eye tracking and hand tracking.

How it works

An LED is built from a semiconductor crystal that has been doped to form two adjacent regions: an n-type region with an excess of electrons and a p-type region with an excess of holes. The boundary between them is the p-n junction. When the diode is forward biased, electrons from the n-side and holes from the p-side drift toward the junction and recombine. Each recombination event drops an electron from a higher energy level to a lower one, and the released energy is emitted as a photon.

The photon energy, and therefore the wavelength and color of the light, is approximately equal to the band gap of the semiconductor. Wide-band-gap materials emit shorter wavelengths (blue and ultraviolet) while narrower-band-gap materials emit longer wavelengths (red and infrared). Early visible LEDs used gallium arsenide phosphide (GaAsP); efficient blue and green LEDs are based on gallium nitride (GaN) and indium gallium nitride (InGaN), and most infrared emitters used in tracking are gallium arsenide (GaAs) devices.

Because the LED is a directly modulated electronic device with no mechanical parts, it can switch on and off very quickly and can be driven in pulses. This property is used in VR and AR tracking, where infrared LEDs are flashed in timed patterns that a camera can synchronize to.

History

The infrared LED predates the visible one. Robert Biard and Gary Pittman at Texas Instruments built an infrared-emitting gallium arsenide diode and filed a patent for it in August 1962; in the same period Robert N. Hall at General Electric demonstrated the first gallium arsenide injection laser, a related diode emitting coherent infrared light. Later that year, on 9 October 1962, Nick Holonyak Jr., working at General Electric's Advanced Semiconductor Laboratory near Syracuse, New York, demonstrated the first visible-spectrum LED. He grew crystals of the alloy GaAsP, and the resulting device emitted red light at room temperature. Holonyak is widely described as the inventor of the first practical visible LED, and the device was the forerunner of commercial LEDs.

For about three decades after 1962, commercially available LEDs were limited to red, then orange, yellow and green, which restricted them to indicator lamps and numeric displays. The missing piece was an efficient blue LED, without which a full-color display or a white light source could not be made. Practical high-brightness blue LEDs based on gallium nitride were developed in the late 1980s and early 1990s; Isamu Akasaki, Hiroshi Amano and Shuji Nakamura shared the 2014 Nobel Prize in Physics for that work. The combination of red, green and blue emitters, and the use of a blue LED with a phosphor to make white light, opened LEDs to general lighting and to color displays.

LEDs in displays

LEDs reach VR and AR displays in two different ways: as a backlight behind a liquid-crystal panel, and as the directly emissive pixel material itself.

LED and Mini-LED backlights for LCD

A liquid-crystal display does not emit its own light. It modulates light from a separate source, and in modern panels that source is an array of LEDs. In a basic LED-backlit LCD the LEDs provide uniform white illumination behind the whole panel. Mini-LED backlights divide that illumination into many small, independently driven zones, a technique called local dimming: the backlight under dark regions of the image is dimmed or switched off while bright regions stay lit, which deepens black levels and raises contrast.

The Pimax Crystal line is a consumer VR example. The Crystal Light is offered in a version whose LCD panels use a Mini-LED backlight with local dimming; this version has 576 dimming zones per panel, which lets the display approach OLED-like black levels in high-contrast scenes. The tradeoff with zoned backlights is blooming, a halo of light around a bright object on a dark background, because each zone covers a block of pixels rather than a single pixel.

OLED and Micro-OLED

An OLED (organic light-emitting diode) is an LED whose emissive layer is a film of organic compound. Each pixel emits its own light, so an OLED display needs no backlight and can produce true blacks by switching individual pixels off. These properties, along with fast response and thin form factor, made OLED common in earlier VR headsets.

Micro-OLED places OLED pixels directly on a silicon backplane (OLED-on-silicon) to make a very small, very high-resolution microdisplay suited to the short throw of a near-eye optical system. The Apple Vision Pro, released in 2024, uses two 1.41-inch Micro-OLED panels supplied with an OLED frontplane from Sony on a silicon backplane from TSMC, with a roughly 7.5-micron pixel pitch and about 23 million pixels across the pair.

Micro-LED

Micro-LED (also written microLED or uLED) uses arrays of microscopic inorganic LEDs as the pixels themselves, rather than the organic emitters of OLED. Like OLED it is emissive and needs no backlight, but because the emitters are inorganic (typically gallium nitride based) the technology can reach much higher brightness and, in principle, longer lifetime and a wider color gamut.

That brightness is the reason Micro-LED is pursued for AR glasses. A see-through AR display must compete with daylight after most of its light is lost in a waveguide combiner, so a microdisplay with an extreme luminance budget is valuable. JBD, a Micro-LED microdisplay maker, reports panel brightness above 10 million nits for green, 2 million nits for blue and 1.5 million nits for red, and its Phoenix series reaches a white-balanced 2 million nits. By the end of 2024 JBD said its Micro-LED engines were used in more than 30 announced AR smart-glasses models, including products from Vuzix, Rokid, INMO and others.

A common point of confusion is that Micro-LED and Micro-OLED are different technologies despite the similar names. Micro-LED pixels are inorganic LED structures; Micro-OLED pixels are organic. As of 2026 full-color Micro-LED microdisplays remain difficult to manufacture, in part because efficient red Micro-LEDs are harder to make than green or blue, and most shipping consumer headsets that use self-emissive microdisplays use Micro-OLED rather than Micro-LED.

The table below summarizes how these display approaches use, or do not use, an LED light source.

Display type	Light source	Backlight needed	Notable VR/AR use
LED / Mini-LED backlit LCD	White LEDs behind the LCD; local-dimming zones	Yes	Pimax Crystal Light (Mini-LED, local dimming)
OLED	Organic LED, one emitter per pixel	No	Earlier VR headsets; emissive panels
Micro-OLED	Organic LED on a silicon backplane	No	Apple Vision Pro, Pimax Crystal Super 8K Micro-OLED
Micro-LED	Inorganic LED, one emitter per pixel	No	AR smart-glasses microdisplays (JBD, Porotech)

Infrared LEDs in tracking

Beyond displays, the largest VR/AR use of LEDs is invisible. Many positional tracking and gaze-tracking systems rely on near-infrared (NIR) LEDs, whose light the user cannot see but a camera can.

Active-marker outside-in tracking

In active-marker outside-in tracking the tracked device carries the LEDs and an external camera observes them. The Oculus Rift CV1 and its Oculus Touch controllers use the Constellation system: a known pattern of infrared LEDs is hidden under the plastic of the headset and controllers, and one or more external IR sensors observe these LEDs to compute pose. Because the geometric layout of the LEDs is known in advance, the system matches each bright spot in the camera image to a specific LED and solves for position and orientation; Meta's engineering description notes that at least four matched LEDs are needed to robustly solve a controller's pose from a single camera image.

PlayStation VR uses the same general idea but in visible light: the original PSVR headset carries nine LEDs on its surface that the PlayStation Camera tracks, along with the illuminated spheres of the PlayStation Move controllers. The use of visible LEDs makes PSVR more sensitive to room lighting than infrared systems such as Constellation.

Contrast with Lighthouse

Not every infrared tracking system puts LEDs on the headset. Valve's Lighthouse system, used by the HTC Vive and the Valve Index, reverses the arrangement: the base stations emit the structured infrared light (a synchronization flash plus swept infrared laser planes), and the headset and controllers carry photodiode sensors, not emitters, that time when each sweep arrives. The Vive headset alone has 32 photodiodes behind its shell. Lighthouse therefore is an example where the LED-like emitters are in the fixed base station and the tracked device only receives light, the inverse of Constellation's active markers.

Eye tracking and hand tracking

Inside the headset, near-infrared LEDs illuminate the eye for eye tracking. Small NIR LEDs placed around each lens produce reflections, called glints, on the cornea; a small camera images the eye and the system computes gaze direction from the positions of the pupil and the glints. Near-infrared is used, commonly around 850 nm, because it is invisible to the wearer and gives good contrast between the pupil and the iris. Research and product eye-tracking modules use arrays of several NIR LEDs per eye for this active illumination.

The same principle helps inside-out hand tracking and controller tracking in the dark. Headset cameras that see in the near-infrared can be aided by IR LED illuminators so that hands and controllers remain trackable in low light; third-party IR illuminators are sold specifically to improve hand tracking on headsets such as the Meta Quest series, which otherwise lose tracking when ambient light is too low.

Current status

As of 2026 LEDs are present in essentially every consumer VR and AR headset, but in shifting roles. LCD panels with LED or Mini-LED backlights remain common in high-resolution PC VR headsets where local dimming narrows the contrast gap with emissive panels. Micro-OLED has become the self-emissive microdisplay of choice for premium mixed-reality headsets such as the Apple Vision Pro. Inorganic Micro-LED is in volume production for monochrome and limited-color AR microdisplays, mainly for AR glasses where its high brightness suits see-through waveguide optics, while full-color, high-yield Micro-LED for wide-field VR is still a development target. Infrared LEDs continue to underpin active-marker tracking, eye tracking and low-light hand tracking across the field.