# head-mounted display

> device used in virtual reality systems

**Wikidata**: [Q1333980](https://www.wikidata.org/wiki/Q1333980)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Head-mounted_display)  
**Source**: https://4ort.xyz/entity/head-mounted-display

## Summary
A **head-mounted display (HMD)** is a wearable device that presents visual information directly to the user's eyes, commonly used in virtual reality (VR), augmented reality (AR), and mixed reality (MR) systems. It is worn on the head and typically includes screens, optics, and sometimes audio components to create an immersive experience.

## Key Facts
- **Definition**: A head-mounted display is a device worn on the head that provides visual output, often used in VR, AR, or MR applications.
- **Parent Class**: It is a subclass of **display device**, which is an output device for presenting information visually.
- **Related Devices**:
  - **Virtual reality headset**: A type of HMD that provides fully immersive virtual environments.
  - **Augmented reality headset**: Overlays digital information onto the real world.
  - **Mixed reality headset**: Combines elements of both VR and AR.
- **Early Example**: *The Sword of Damocles* (1968) is considered the first head-mounted display.
- **Aliases**: Also known as **HMD, Datenhelm, Videobrille, or VR-Helm** in different contexts.
- **Worn On**: Designed to be worn on the **head**.
- **Notable Models**:
  - **VPL EyePhone LX** (early VR HMD)
  - **Sony HMZ-T1** (stereoscopic display)
  - **Avegant Glyph** (retinal projection-based HMD)
  - **Saab AddVisor 150** (military/aviation HMD)

## FAQs
### Q: What is a head-mounted display used for?
A: Head-mounted displays are primarily used in **virtual reality (VR), augmented reality (AR), and mixed reality (MR)** applications, providing immersive visual experiences for gaming, training, simulation, and professional use.

### Q: What was the first head-mounted display?
A: *The Sword of Damocles*, developed in **1968**, is recognized as the first head-mounted display, created by Ivan Sutherland and his team.

### Q: How does a head-mounted display differ from a VR headset?
A: While all **VR headsets** are head-mounted displays, not all HMDs are VR-specific—some are designed for **augmented reality (AR)** or **mixed reality (MR)**, which blend digital content with the real world.

### Q: Are head-mounted displays only for gaming?
A: No, HMDs are used in **military training (e.g., Saab AddVisor 150), medical simulations, aviation, engineering, and industrial design**, in addition to gaming and entertainment.

### Q: What are some well-known head-mounted displays?
A: Notable examples include the **Oculus Rift (VR)**, **Microsoft HoloLens (AR)**, **Sony HMZ-T1 (stereoscopic display)**, and **Avegant Glyph (retinal projection HMD)**.

## Why It Matters
Head-mounted displays revolutionize how humans interact with digital content by placing immersive visuals directly in the user’s field of view. They enable **realistic simulations for training** (e.g., flight, surgery, or combat), **enhanced gaming experiences**, and **new forms of remote collaboration**. In industries like **aerospace, healthcare, and manufacturing**, HMDs improve precision and safety by overlaying critical data onto real-world views. For consumers, they unlock **virtual travel, social VR, and interactive storytelling**, blurring the line between physical and digital realities. As AR and VR technologies advance, HMDs are becoming lighter, more affordable, and more integrated into daily life, potentially redefining communication, education, and entertainment.

## Notable For
- **First HMD**: *The Sword of Damocles* (1968) pioneered the concept of wearable immersive displays.
- **Versatility**: Used across **VR, AR, and MR**, serving gaming, military, medical, and industrial applications.
- **Wearable Form Factor**: Designed to be **lightweight and head-worn**, unlike traditional monitors.
- **Stereoscopic Vision**: Many HMDs (e.g., Sony HMZ-T1) support **3D depth perception** for enhanced immersion.
- **Military & Aviation Use**: Devices like the **Saab AddVisor 150** provide pilots and soldiers with real-time data overlays.

## Body
### **Definition and Classification**
A **head-mounted display (HMD)** is a display device worn on the head, positioning screens close to the user’s eyes to create an immersive visual experience. It belongs to the broader category of **display devices** but is distinct due to its wearable nature and direct alignment with the user’s line of sight.

HMDs are further categorized based on their application:
- **Virtual Reality (VR) Headsets**: Fully immerse the user in a digital environment (e.g., Oculus Rift).
- **Augmented Reality (AR) Headsets**: Overlay digital elements onto the real world (e.g., Microsoft HoloLens).
- **Mixed Reality (MR) Headsets**: Merge real and virtual worlds, allowing interaction with both (e.g., Magic Leap).

### **Historical Development**
- **1968**: *The Sword of Damocles*, developed by **Ivan Sutherland**, is the first known HMD. It used primitive mechanics to track head movements and display simple wireframe graphics.
- **1980s–1990s**: Early commercial HMDs like the **VPL EyePhone LX** emerged, though they were bulky and expensive.
- **2010s**: Consumer VR took off with devices like the **Oculus Rift (2012)** and **HTC Vive (2015)**, making HMDs more accessible.
- **2020s**: Advances in **optics, tracking, and wireless technology** led to standalone HMDs (e.g., Meta Quest) and lightweight AR glasses.

### **Technical Features**
- **Display Technology**:
  - **LCD/OLED screens**: Common in modern VR headsets for high-resolution imagery.
  - **Retinal projection**: Used in devices like the **Avegant Glyph** to project images directly onto the retina.
  - **Stereoscopic 3D**: Dual displays (one per eye) create depth perception (e.g., Sony HMZ-T1).
- **Tracking Systems**:
  - **Inside-out tracking**: Cameras on the HMD map the environment (e.g., Oculus Quest).
  - **Outside-in tracking**: External sensors track the HMD’s position (e.g., HTC Vive with base stations).
- **Field of View (FoV)**: Typically ranges from **90° to 120°** in consumer VR headsets, with professional models offering wider angles.
- **Refresh Rate**: High-end HMDs support **90Hz–120Hz** to reduce motion sickness.

### **Applications**
- **Gaming & Entertainment**: VR headsets like the **PlayStation VR** and **Valve Index** provide immersive gaming experiences.
- **Military & Aviation**:
  - **Saab AddVisor 150**: Used by pilots for helmet-mounted targeting and flight data.
  - **U.S. Military**: HMDs like the **Scorpion HMIT** assist soldiers with tactical information.
- **Medical Training**: Surgeons use HMDs for **surgical simulations** and remote assistance.
- **Industrial & Engineering**: AR HMDs overlay **3D models and instructions** for assembly and repair tasks.
- **Education**: VR field trips and interactive learning environments.

### **Challenges and Limitations**
- **Comfort & Weight**: Prolonged use can cause **fatigue or discomfort** due to pressure on the head.
- **Motion Sickness**: Latency or low refresh rates may induce nausea in some users.
- **Cost**: High-end HMDs remain expensive, though prices have decreased with mass-market adoption.
- **Battery Life**: Standalone wireless HMDs often have limited battery duration.

## Schema Markup
```json
{
  "@context": "https://schema.org",
  "@type": "Thing",
  "name": "Head-mounted display",
  "description": "A wearable device that presents visual information directly to the user's eyes, used in virtual reality, augmented reality, and mixed reality systems.",
  "url": "https://en.wikipedia.org/wiki/Head-mounted_display",
  "sameAs": [
    "https://www.wikidata.org/wiki/Q844250",
    "https://en.wikipedia.org/wiki/Head-mounted_display"
  ],
  "additionalType": "DisplayDevice"
}

## References

1. Freebase Data Dumps. 2013
2. KBpedia