Head-mounted display: Difference between revisions

*   '''Display Technology''': The type of display panel used significantly impacts image quality. Common types include:

    *   [[LCD]] (Liquid Crystal Display): Often offers higher pixel density (reducing the [[screen-door effect]]) and potentially lower cost, but may have slower response times and lower contrast compared to OLED. Modern LCDs in VR often use fast-switching technologies and [[Quantum dot display|quantum dots]] for better color.<ref name="LCDvsOLED_VR">AR/VR Tips. "LCD vs OLED VR Headsets: Which Screen is Best?". Retrieved 2023-10-27. [https://arvrtips.com/lcd-vs-oled-vr-headsets/ Link]</ref>

    *   [[OLED]] (Organic Light-Emitting Diode): Provides true blacks (infinite contrast ratio), vibrant colors, and very fast pixel response times (reducing motion blur or ghosting). Can be more susceptible to "[[Screen burn-in|burn-in]]" over long periods and may use [[PenTile matrix family|PenTile]] [[Subixel rendering|subpixel layouts]] affecting perceived sharpness.

    *   [[Micro-OLED]] / [[OLEDoS]] (OLED-on-Silicon): Very small, high-resolution OLED displays built directly onto silicon wafers. Offer extremely high pixel densities (PPD) and brightness, often used in high-end or compact HMDs (e.g., [[Bigscreen Beyond]], [[Apple Vision Pro]]).<ref name="MicroOLED_Intro">OLED-Info. "MicroOLED displays". Retrieved 2023-10-27. [https://www.oled-info.com/microoled Link]</ref><ref name="microoled2025">Systems Contractor News (23 Apr 2025). "Dual micro-OLED displays grow within the AR/VR headset market". Retrieved 2024-05-15. [https://www.svconline.com/proav-today/dual-micro-oled-displays-grow-within-the-ar-vr-headset-market Link]</ref>

    *   [[MicroLED]]: An emerging technology promising high brightness, efficiency, contrast, and longevity, potentially surpassing both LCD and OLED for HMDs.

*   '''[[Resolution]]''': The number of [[pixel]]s on the display(s), usually specified per eye (e.g., 2064 x 2208 per eye for Meta Quest 3) or sometimes as a total resolution. Higher resolution reduces the [[screen-door effect]] (the visible grid pattern between pixels) and increases image sharpness. [[Pixels Per Degree]] (PPD) is often a more perceptually relevant metric, combining resolution and FOV. Human visual acuity corresponds to roughly 60 PPD; current consumer VR is typically in the 20-35 PPD range, while high-end devices like Vision Pro exceed 40 PPD centrally.

*   '''[[Refresh Rate]]''': The number of times per second the display updates the image, measured in Hertz (Hz). Higher refresh rates (e.g., 90Hz, 120Hz, 144Hz) lead to smoother motion, reduced flicker, and can help mitigate motion sickness. 90Hz is often considered a comfortable minimum for VR. Low persistence displays (where pixels are illuminated only for a fraction of the refresh cycle) are crucial in VR to reduce motion blur during head movements.<ref name="LowPersistence">Abrash, Michael (2014-07-28). "Understanding Low Persistence on the DK2". Oculus Developer Blog. Retrieved 2023-10-27. [https://developer.oculus.com/blog/understanding-low-persistence-on-the-dk2/ Link]</ref>

*   '''[[Field of View]] (FOV)''': The extent of the visual field visible through the HMD, usually measured horizontally, vertically, and/or diagonally in degrees. Human binocular vision covers roughly 200-220° horizontally (with ~120° stereoscopic overlap). VR HMDs aim for a wide FOV (typically 100°-110° horizontally for consumer devices, sometimes wider like [[Pimax]] headsets) to enhance immersion. AR OHMDs often have a much narrower FOV (e.g., 30°-55°) due to the challenges of see-through optics.<ref name="VR_FOV_Comparison">VR Compare. "Headset Feature: Field of View". Retrieved 2023-10-27. [https://vr-compare.com/headsetfeature/fieldofview Link]</ref>

*   '''Optics / [[Lens|Lenses]]''': The lenses used heavily influence FOV, image sharpness (center-to-edge), [[Chromatic aberration|chromatic aberration]], geometric distortion, and physical characteristics like size and weight.

    *   [[Aspheric lens|Aspheric Lenses]]: Simple, often used in early or budget HMDs. Can be bulky.

    *   [[Fresnel lens|Fresnel Lenses]]: Use concentric rings to reduce thickness and weight compared to simple aspheric lenses while maintaining a short focal length. Common in many VR HMDs (e.g., Rift CV1, Vive, Quest 2), but can introduce visual artifacts like concentric rings and "[[God rays]]" (stray light scattering off the ridges).

    *   [[Pancake lens|Pancake Lenses]]: A newer, more complex folded optic design using polarization. Allow for significantly shorter distances between the display and lens, enabling much slimmer and lighter HMD designs. Often offer improved edge-to-edge clarity but can be less light-efficient, requiring brighter displays. Used in devices like Meta Quest Pro, Pico 4, Bigscreen Beyond.<ref name="PancakeOptics">Guttag, Karl (2021-12-09). "VR Optics (Part 1) – Brief History and Pancake Lenses". KGOnTech. Retrieved 2023-10-27. [https://kguttag.com/2021/12/09/vr-optics-part-1-brief-history-and-pancake-lenses/ Link]</ref><ref name="optics2023">Expand Reality (05 Oct 2023). "Pancake vs Fresnel Lenses in VR Headsets". Retrieved 2024-05-15. [https://landing.expandreality.io/pancake-vs.-fresnel-lenses-in-vr-headsets-advanced-optics-for-vr Link]</ref>

    *   [[Waveguide (optics)|Waveguides]] (AR): Used in many see-through OHMDs (e.g., HoloLens, Magic Leap). Light from a microdisplay is injected into a thin piece of glass or plastic and then directed out towards the eye using [[Diffractive optics|diffractive]] or reflective elements, allowing the user to see the real world through the waveguide. Achieving wide FOV and high efficiency with waveguides is challenging.<ref name="AROpticsReview"/><ref name="waveguide2022">Radiant Vision Systems (11 Jan 2022). "Ride the Wave: AR Devices Rely on Waveguides". Retrieved 2024-05-15. [https://www.radiantvisionsystems.com/blog/ride-wave-augmented-reality-devices-rely-waveguides Link]</ref>

    *   [[Beam splitter|Beam Splitters / Birdbaths]] (AR): A simpler see-through optic where a partially reflective mirror combines light from a display with the view of the real world. Often bulkier and may have a smaller FOV or less uniform transparency than waveguides. Used in devices like Google Glass (using a prism variant) and Nreal/XREAL Air.<ref name="BirdbathOptics">Guttag, Karl (2019-04-01). "HoloLens 2 (HL2) and AR Optics in General (Part 1)". KGOnTech. Retrieved 2023-10-27. [https://kguttag.com/2019/04/01/hololens-2-hl2-and-ar-optics-in-general-part-1/ Link]</ref>

    *   [[Holographic Optical Elements]] (HOEs): Thin, lightweight optical components created using holographic recording techniques, capable of performing complex functions like focusing, diffusion, or beam steering. Used in some advanced AR displays.

*   '''[[Interpupillary distance]] (IPD) Adjustment''': The distance between the centers of the pupils varies between individuals (typically 54-72mm for adults). HMDs need to accommodate this for optimal clarity, comfort, and correct stereo rendering. Adjustment can be:

    *   Physical/Manual: Lenses can be moved closer together or further apart, often via a slider or dial (e.g., Valve Index, Quest 3). Continuous adjustment allows finer tuning.

    *   Stepped: Some HMDs offer discrete IPD steps (e.g., original Quest, Quest 2).

    *   Software-based: The rendering viewpoint separation is adjusted in software (less common or effective for major mismatches without physical lens movement).

    *   Automatic: High-end systems might use eye-tracking to measure IPD and adjust automatically or prompt the user.

*   '''[[Eye tracking]]''': Sensors (typically small infrared cameras) inside the HMD track the user's gaze direction. This enables:

    *   [[Foveated rendering]]: Rendering the area where the user is looking at full resolution, and the periphery at lower resolution, saving significant computational power.<ref name="FoveatedRenderingNvidia">NVIDIA Developer. "NVIDIA Variable Rate Shading (VRS) & Foveated Rendering". Retrieved 2023-10-27. [https://developer.nvidia.com/vrworks/graphics/foveatedrendering Link]</ref>

    *   Improved Social Interaction: [[Avatar]]s can mimic the user's eye movements, enhancing realism in social VR.

    *   Automatic IPD adjustment.

    *   Gaze-based interaction as an input method.

*   '''Connectivity''': How the HMD connects to the processing unit (if not standalone).

    *   Wired: Typically [[USB]] (often Type-C for power/data) and [[DisplayPort]] or [[HDMI]] for high bandwidth video. Offers highest fidelity and lowest latency but restricts movement.

    *   Wireless: Uses [[Wi-Fi]] (often Wi-Fi 6/6E/7) or proprietary radio frequencies (e.g., older WiGig solutions) to stream video and data. Offers freedom of movement but requires video compression (potentially affecting quality) and can introduce latency. Examples: [[HTC Vive Wireless Adapter]], [[Meta Air Link]], [[Virtual Desktop]].<ref name="WirelessVRComparison">Heaney, David (2022-01-20). "Wireless PC VR Comparison: Air Link vs Virtual Desktop vs Vive Wireless". UploadVR. Retrieved 2023-10-27. [https://uploadvr.com/wireless-pc-vr-comparison/ Link]</ref>

*   '''Audio''': Sound is crucial for immersion. HMDs may feature:

    *   [[Spatial Audio]]: 3D audio rendering techniques that make sounds appear to come from specific locations in the virtual environment. Supported via various output methods.

    *   Integrated [[Speaker]]s: Often open-ear [[Near-field communication|near-field]] speakers built into the strap or near the ears, providing spatial audio without blocking external sounds (e.g., Valve Index, Quest series).

    *   [[Headphone]] Jack (3.5mm): Allows users to connect their own headphones or earbuds.

    *   Integrated Headphones: High-fidelity on-ear or over-ear headphones attached to the HMD (e.g., original Rift CV1, HP Reverb G2).

    *   [[Microphone Arrays]]: Multiple microphones for clear voice input, communication in multiplayer apps, voice commands, and potentially noise cancellation.

*   '''[[Ergonomics]]''': Factors affecting comfort during extended use:

    *   Weight: Lighter is generally better (most consumer HMDs are 400-700g).

    *   Weight Distribution: Balanced weight (front-to-back) is often more important than total weight. Battery placement in standalone HMDs (e.g., rear-mounted) can improve balance.

    *   Strap Design: Different mechanisms (soft elastic straps, rigid "halo" straps, top straps) distribute pressure differently.

    *   Facial Interface: Foam or fabric padding, material breathability, light blocking. Options/space for glasses wearers or [[prescription lens]] inserts.