Head-up display

A head-up display (HUD, also written heads-up display) is a transparent display that places information in the user's line of sight, so that it can be read while the user keeps looking out at the world instead of down at a panel. In aviation the term describes a display that projects flight information directly into the pilot's line of sight on a transparent glass or plastic screen called a combiner, which reflects the image toward the eyes without blocking the view outside. HUDs have been flown in military aircraft since the early 1960s and have been fitted to production cars since 1988.

The HUD is closely related to optical see-through augmented reality. In his 1997 survey of the field, Ronald Azuma compared optical see-through head-mounted displays to the HUDs of military aircraft, the difference being that the combiners are attached to the head; such headsets had "sometimes been described as a 'HUD on a head'". The 1992 Boeing paper by Thomas Caudell and David Mizell that introduced the term "augmented reality" was titled "An Application of Heads-Up Display Technology to Manual Manufacturing Processes". The term is now also applied to smart glasses such as the Meta Ray-Ban Display, which show a small, fixed image in one eye rather than placing virtual objects in the world.

Reviewed 27 September 2026. Checked every cited source (BAE, RAeS, Aviation Today, TI DLPA098, Zhou et al. 2024, SAE 890288, PistonHeads, WardsAuto, NASA TP-1711, FAA AM-19/13, Azuma 1997, Caudell and Mizell 1992, Military & Aerospace Electronics, RTX, Boeing, Engadget, UploadVR, Meta developer pages) against the claims, figures and quotes cited to them. About review dates.

How it works

An aviation HUD system has four main parts: a computer that processes aircraft data in real time, a projector, the combiner, and a control panel. The projected image is collimated, meaning its light rays are made to appear parallel out to infinity instead of converging on the physical display surface.

Automotive HUDs follow the same principle but usually use the windshield as the combiner. A 2024 review of automotive HUDs by Chen Zhou and colleagues at Soochow University describes the hardware as a picture generation unit (PGU), which creates the image using a TFT-LCD, digital light processing (DLP), liquid crystal on silicon (LCoS) or micro-LED device, and an optical system that projects a virtual image beyond the windshield. The optics fold the light path, magnify the image, form the eye box and correct the aberration introduced by the curved windshield.

Eye box

Because the image is formed by optics fixed in the vehicle, the user's eyes must stay inside a limited volume, the eye box, to see it. Modern aircraft HUDs allow head movement within roughly 5 inches laterally, 3 inches vertically and 6 inches longitudinally. A 2018 Texas Instruments white paper explains that in a car HUD the eye box is the exit pupil of the optical system and must be large enough for both eyes, plus variation in eye spacing, head position and driver height. It is often as large as 140 mm x 60 mm and in many cases has to be adjusted mechanically to the driver's head position. That size is one of the main reasons HUD optics are bulky.

History

Military aviation

BAE Systems traces the first HUD concepts to the Second World War, when they were drafted to help pilots locate targets. The Royal Aeronautical Society dates BAE's HUD line to 1958 and the Strike Sight system for the Blackburn Buccaneer, described as "the worlds first HUD in operational service". According to BAE, its predecessor Elliott Flight Automation, together with Cintel, developed and manufactured that system, which entered service on the Buccaneer in 1961. HUDs became widespread in military aircraft during the 1960s.

BAE later supplied HUDs for aircraft including the F-16, F-22, Eurofighter Typhoon and C-17, and stated in 2016 that it had delivered more than 14,500 HUDs. The company lists night vision, diffractive optics, computer-generated holography and waveguide optics among the technologies it added to HUDs over the following decades.

The next step moved the HUD onto the pilot's head. BAE describes its Striker II helmet-mounted display as transferring the functions of a fixed HUD to the helmet, with the image projected onto the visor. The F-35 was described in 2019 as the first tactical fighter in 50 years without a traditional HUD: its helmet blends head-up display, helmet-mounted display and visor-projected night vision, and the aircraft's Distributed Aperture System streams real-time imagery from six infrared cameras around the airframe to the helmet. In February 2024 Collins Elbit Vision Systems delivered its 3,000th F-35 Gen III Helmet Mounted Display System, which it describes as the pilot's primary display system.

Civil aviation

In 2001 Boeing announced that Rockwell Collins' Flight Dynamics HGS 4000 head-up guidance system would be standard on its Boeing Business Jets. The system displays flight data on a holographic transparent glass combiner between the pilot and the windscreen and provides approach and landing guidance, low-visibility takeoff guidance, runway deceleration cueing, runway length remaining and an unusual attitude recovery cue; it can also show raster images from enhanced and synthetic vision systems. According to Radiant Vision Systems, the Boeing 787 was the first large commercial aircraft to offer a HUD as standard equipment.

Cars

The first production HUD in a car appeared in the 1988 Oldsmobile Cutlass Supreme Indianapolis 500 Pace Car parade convertibles. Its General Motors designers described a vacuum fluorescent display tube and reflective optics that used the standard production windshield as the final optical element. It produced a virtual image of a digital speedometer and selected warning telltales just above the hood line, at roughly the distance of the front bumper. PistonHeads reports that the system was unveiled in May 1988; Nissan had finished its first HUD in December 1987 but did not offer it until late 1988, and Toyota (1991 Crown Majesta) and BMW (2003) followed.

Zhou and colleagues divide automotive HUDs into three generations: combiner HUDs (C-HUD) with a separate optical panel above the dashboard, windshield HUDs (W-HUD), and augmented reality HUDs (AR-HUD). Because a C-HUD image sits inside the car, the driver still has to shift focus away from the road. Their review gives these typical figures:

Type	Field of view	Virtual image distance	Volume
C-HUD	under 5 x 1.4 degrees	about 1 m	under 2 L
W-HUD	6 x 2 degrees	under 4.5 m	under 4 L
AR-HUD	over 13 x 5 degrees	over 7 m	under 10 L
Ideal target	over 20 x 10 degrees	over 20 m	under 3 L

The TI white paper notes that many conventional car HUDs have a field of view of about 5 degrees with the image placed about 2.5 m in front of the driver, just over the hood, and mainly repeat instrument-cluster data such as speed. Carmakers want the image to span the width of the road (more than 15 degrees) and sit on the road surface up to 20 m ahead, so that driver-assistance information can be overlaid on the scene. In July 2020 Mercedes-Benz announced an AR-HUD for its next-generation S-Class, projecting animated navigation arrows over the road at a virtual distance of 10 m, with a display area equivalent to a 77-inch monitor. A longer image distance reduces how often the driver's eyes have to change focus between the road and the display. Short image distances also make the two surfaces of the windshield produce a visible ghost image, a problem Zhou and colleagues note mostly disappears when the image is far enough away.

Human factors

Putting information over the outside view has known costs as well as benefits. In a 1980 NASA study, eight airline pilots flew approaches in a fixed-base Boeing 727 simulator with and without a flight-path HUD. Their mean response time to an unexpected obstacle on the runway was 4.13 seconds with the HUD against 1.75 seconds without it, and two of the pilots did not see the obstacle at all with the HUD. In every condition, however, both vertical and lateral tracking were better with the HUD than with conventional instruments.

A 2018 literature review for the Federal Aviation Administration by Christopher Wickens and Michelle Yeh summarized later work. A meta-analysis of 22 studies by Fadden, Ververs and Wickens (2001) found an overall significant benefit for the head-up location, because pilots scanned less, but a small cost to the detection of discrete events, observed only during landing and statistically significant only when the event was unexpected. Conformal, scene-linked symbology, which overlays and moves with its real-world counterparts as the aircraft rotates and translates, reduced that cost without removing it. A very bright HUD image can also make traffic seen through it harder to see. The authors concluded that "the compellingness of the HUD does not appear to be a major concern, and its advantages far outweigh its costs". The same review cites a study in which a head-mounted see-through display slightly disrupted the detection of unexpected events compared with a hand-held display.

Relationship to augmented reality

Azuma defined augmented reality by three characteristics: it combines real and virtual, it is interactive in real time, and it is registered in 3-D. He noted that military aircraft and helicopters had long used HUDs and helmet-mounted sights to superimpose vector graphics on the pilot's view, and that these graphics were sometimes registered with targets in the environment to aim weapons. He also described fixed combiners that the user looks through, "typical of Head-Up Displays on military aircraft", as one of the optical configurations for AR.

Caudell and Mizell's Boeing prototype, which they called the "HUDset", combined a see-through head-mounted display with head position sensing and a registration system for the workplace. By tracking the six degrees of freedom of the head, the system kept a graphic such as an arrow marking a drill hole fixed at the same physical location as the worker moved, and the authors called the technology "augmented reality". Aircraft HUD graphics are sometimes registered with targets, but many HUDs do without registration of this kind; HUD glasses such as the Meta Ray-Ban Display provide a small display fixed in the user's vision rather than attaching content to objects in the world.

Smart glasses

Early smart glasses were described as head-up displays. Reviewing the Google Glass Explorer Edition in 2013, Engadget wrote that "A heads-up display seems like a natural fit, and thus we have Google Glass". Its display sits above the right eye, with a panel beaming light onto a reflective surface angled at 45 degrees; Google did not officially specify the resolution, but developers worked with a 640 x 360 pixel array.

The same distinction is drawn for current products. In its review of the Meta Ray-Ban Display, UploadVR called the product HUD glasses and explained that they "can't place virtual 3D objects into the real world, nor even 2D virtual interfaces". Its display is visible only to the right eye, covers about 14 degrees horizontally and vertically (20 degrees diagonal) at 600 x 600 pixels, reaches a maximum brightness of 5000 nits, and is translucent enough that the real world stays visible through it.

HUDs in VR and mixed reality software

Meta's design guidelines for its headsets note that displaying information around the user's view "like a heads-up display (HUD), is a popular method used in first-person games", but that in passthrough mixed reality such information can tire the user quickly and reduce usability. The guidelines advise developers to avoid locking HUD-style content to head movement and to anchor it in space or have it follow the user loosely with smoothing animation. In a 2017 article on VR design patterns, Chris Pruett of Oculus wrote that hanging HUDs and subtitles in space "can cause depth cue conflict" if done improperly, and that the best solution seen so far was to attach such elements to objects in the world, for example putting subtitles on a wall or a life bar on the user's arm.

See also

• Helmet-mounted display
• Head-mounted display
• Optical see-through head-mounted display
• Optical combiner
• Eye box
• Virtual image
• Waveguide display
• Smart glasses