Head-up display

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A head-up display (HUD) is a transparent screen that shows important information right in a viewer’s line of sight. By keeping eyes forward, you don’t have to look away to check instruments, and you don’t need to refocus when looking back out at work or the sky. HUDs started in military aviation but are now common in commercial planes, cars, and other professional uses. They also helped pave the way for augmented reality, though they don’t always perfectly align virtual data with the real world.

How a typical HUD works
- Projector unit: creates an image that appears to come from infinity, using a lens or mirror and a display like LED or LCD.
- Combiner: a special piece of glass at eye level that reflects the projected image so you can see both the outside view and the HUD data at the same time.
- Computer: feeds the HUD with data and creates the symbols you see (like speed, altitude, and horizon).

Types and evolution
- Fixed HUDs sit in the cockpit; head-mounted displays (HMDs) or helmet-mounted displays move with your head.
- Some modern fighters use both a HUD and an HMD; the F-35 relies mainly on the HMD.
- HUD technology has evolved through four generations and now uses micro-displays such as LCD, LCoS, DMD, and OLED.

From sights to flight data
- HUDs trace their roots to early optical sights for aircraft. Over time they added flight data and navigation to a single glance range.
- In the 1950s–1960s, the UK and other countries helped develop standardized HUD symbols to make it easier for pilots to switch between aircraft.
- By the 1970s–1980s, HUDs moved from military to commercial aviation, and the first car HUD appeared in 1988 (Oldsmobile Cutlass Supreme).
- Today, many large passenger planes, including newer Boeing and Airbus models, use HUDs or HUD-like systems, and some have optional enhanced or synthetic vision features.

What HUDs show
- Typical cockpit data: airspeed, altitude, horizon line, heading, and turn/bank indicators.
- Advanced displays add flight path vectors, flight guidance cues, and sometimes a “tunnel” or path line to show the best approach or flight path.
- Some HUDs pair with synthetic vision systems (SVS) that render a 3D view of terrain and obstacles from navigation data, often in monochrome green.

Enhanced and augmented vision
- Enhanced Vision Systems (EVS) overlay live outside-camera images (usually infrared) onto the HUD to improve visibility in poor conditions. For safety, the overlay must be accurately registered with reality to avoid misleading pilots.
- SVS and EVS can help with low-visibility landings and complex navigation, and they’re designed to work with the HUD to keep crucial cues in the pilot’s line of sight.
- In cars, HUDs have expanded to display speed, navigation, and sometimes night-vision imagery. Automotive HUDs are common, but unlike aircraft HUDs, they aren’t parallax-free and can be affected by sunglasses with polarized lenses.

AR and new display tech
- Some companies are exploring holographic and retinal-display approaches (display data directly on the eye or through holographic optics) to widen the field of view and reduce the size of the device.
- Ideas include AR-HUDs that blend real-world views with computer graphics, eye-tracking, and even hands-free gesture control.
- Military and civilian experiments include helmet-mounted displays for tanks and other vehicles, as well as language translation and other assistive apps.

In short
HUDs bring critical information into the pilot’s or driver’s direct line of sight, helping with situational awareness, safer landings, and quicker responses. From early gun sights to modern cockpit data and AR-assisted displays, HUD technology keeps eyes on the world while still providing the data you need.