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Nit (unit)

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The nit (symbol nt) is a name for the candela per square metre (cd/m2), the SI derived unit of luminance. One nit equals one candela per square metre.[1][2] The name is not part of the SI, but it is in wide use.[3]

In virtual reality (VR) and augmented reality (AR), nits describe how bright a display panel, an optical engine or the final image at the eye is. These figures can differ by orders of magnitude for the same device, because head-mounted display optics pass only part of the panel's light to the eye. An AR waveguide can need over a million nits from the display to put 10,000 nits into the eye.[4] For optical see-through AR, the luminance needed also depends on the brightness of the real scene behind the image. Review papers estimate that, on a sunny day, the display needs at least 10,000 nits for a 3:1 ambient contrast ratio, or 30,000 nits for 10:1, before optical losses are counted.[5][6]

Reviewed 11 October 2026. Definition, conversion factors and every nit figure checked against the cited BIPM, CIE, NIST, IALA, IEC and ITU pages, the Xiong 2021, Hsiang 2022, Matsuda 2022 and Erickson 2020 papers (DOIs via Crossref), and the cited press and maker pages. About review dates.

Definition

The International Commission on Illumination (CIE) defines luminance as the density of luminous intensity with respect to projected area, in a specified direction, at a specified point on a real or imaginary surface. Its unit is the candela per square metre, which the CIE also writes as lm·m-2·sr-1 (lumens per square metre per steradian).[7] Put simply, luminance is the amount of light traveling through or reflected from a surface, and it depends on the viewing angle.[8]

The candela is the SI base unit of luminous intensity. In the current SI, described in the 9th edition (2019) of the SI Brochure, it is defined by fixing the luminous efficacy of monochromatic radiation of frequency 540 x 1012 Hz, Kcd, at exactly 683 lm/W. In practice, one candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation at that frequency with a radiant intensity of 1/683 W/sr in that direction.[9][2]

Luminance is a photometric quantity. Radiometric measurements are weighted by CIE spectral luminous efficiency functions, which model the eye's sensitivity to different wavelengths, and are then scaled by Kcd.[2] Two sources with the same radiance can therefore have different luminances if their spectra differ. Luminance is also distinct from perceived brightness, which the CIE defines separately as an attribute of visual perception: how much light an area appears to emit, transmit or reflect.[10]

The CIE notes that, in a lossless optical path, luminance divided by the square of the refractive index (a quantity it calls basic luminance) stays constant along a beam.[7] In near-eye display design, Xiong and colleagues describe the trade-off between field of view and eye box in geometric optics as a consequence of etendue conservation, and note that a larger eye box or field of view usually lowers image brightness.[5]

Name and related units

The name comes from the Latin niteo, "to shine". According to Russ Rowlett's dictionary of units at the University of North Carolina at Chapel Hill, the nit is not approved as part of the SI but has been approved by the CIE since 1947. Rowlett also lists "meterlambert" as an occasional alternative name, by analogy with the footlambert.[3] The IALA dictionary of marine aids to navigation, which credits the CIE as its reference, says that the candela per square metre "is sometimes called Nit" and gives the symbol nt.[1]

NIST gives these conversion factors for older luminance units:[11]

Unit Symbol Value in cd/m2 (nits)
nit nt 1 (by definition)[1]
footlambert fL 3.426 259[11]
candela per square inch cd/in2 1,550.003[11]
lambert L 3,183.099[11]
stilb sb 10,000[11]

Ambient light is usually measured as illuminance, in lux (lumens per square metre), which is the light falling on a surface rather than the light leaving it.[8] To compare ambient light with display luminance, AR display researchers often convert lux to nits by dividing by pi, which assumes a Lambertian (perfectly diffuse) emission profile.[5]

Measurement

The BIPM's mise en pratique for the candela describes how the candela per square metre is realized in practice. The unit can be realized with a diffuse Lambertian source, either by calculating the luminance of a blackbody radiator from its temperature with Planck's law, or by measuring the luminance of a uniformly diffusing surface produced by an integrating sphere or a white reflecting surface.[2]

The International Electrotechnical Commission published IEC 63145-20-10 on 16 August 2019. It sets standard measurement conditions and methods for the optical properties of eyewear displays that use virtual image optics, covering both non-see-through VR goggles and see-through AR glasses. Contact-lens displays and retina direct projection displays are outside its scope.[12]

Nits in VR and AR hardware

Panel brightness and brightness at the eye

A nit figure for a headset or pair of glasses can refer to the panel, the light engine or the image after the optics. Industry analyst Karl Guttag measured the Nreal Light birdbath glasses and reported that "the nits to the eye are only ~15% of the nits from the display", adding that birdbath optics typically pass about 15 percent of the display's light to the eye.[13] In VR, the half mirror in pancake optics limits efficiency to a maximum of 25 percent, so at most about a quarter of the panel's light reaches the eye even before other losses. The limit is stated in a news release on a 2024 paper in Opto-Electronic Advances, "Breaking the optical efficiency limit of virtual reality with a nonreciprocal polarization rotator", by Yuqiang Ding, Zhenyi Luo, Garimagai Borjigin and Shin-Tson Wu.[14]

Waveguides lose far more light. Mojo Vision's Nikhil Balram told IEEE Spectrum in 2023 that waveguide optics are less than 1 percent efficient, so delivering 10,000 nits to the eye for a sunlit scene needs over a million nits from the display. He said a typical customer requirement for the company's MicroLED panels was 1 million nits.[4] Xiong and colleagues rate AR combiners by output luminance divided by input luminous flux, in nits per lumen, noting that for a fixed input flux the output luminance depends on the field of view and exit pupil. They gave typical values of about 50-200 nit/lm for diffractive waveguides and about 650 nit/lm for a partial-mirror combiner with two-dimensional exit pupil expansion, compared with about 4,000 nit/lm for conventional geometric optics with a large form factor.[5] Waveguide makers also quote nits per watt of light-engine power. At CES 2026, Lumus said an updated version of its Z-30 optical engine weighed 11 g and had a luminance efficiency of more than 8,000 nits per watt.[15]

Product listings sometimes give both kinds of number. Xreal's store page for the Xreal One, which uses Sony Micro-OLED panels, lists 600 nits as its "Highest Perceived Brightness", while an image on the same page refers to a "5000 nits peak brightness display".[16] Jade Bird Display reported MicroLED panel brightness records in 2024 of 10 million nits for green, 2 million for blue and over 1.5 million for red, while rating its Hummingbird I polychrome module at 6,000 nits through diffractive waveguides.[17]

Panel ratings also depend on drive conditions. Sony Semiconductor Solutions announced the ECX350F, a 0.44-type 1920 x 1080 OLED microdisplay for AR glasses, in September 2024 with a peak luminance of 10,000 cd/m2, specified at 100% duty drive and described as about double that of its conventional model.[18] Duty ratio matters in VR because headsets light each frame only briefly to reduce motion blur (see persistence). Hsiang and colleagues write that a low duty ratio of 10-20% illumination is key to suppressing motion blur, and that a shorter emission time needs an instantaneously brighter backlight, with higher drive current and power consumption.[6] According to the Xiong review, Sony proposed in 2019 to add newly designed InZnO cathodes and microlens arrays to its white OLED microdisplays, which raised their peak brightness from 1,600 to 5,000 nits.[5]

Virtual reality headsets

Because a VR headset blocks ambient light, Hsiang and colleagues write that 150-200 nits received by the eye is acceptable after optical losses are considered, and the 2021 Xiong review gives about 150-200 cd/m2 as the display brightness of a typical VR headset.[6][5] Writing in 2022, UploadVR put the luminance of Meta's Meta Quest 2 at about 100 nits.[19]

These levels are far below the range of the real world. Hsiang and colleagues give the range of the human visual system as running from starlight at about 10-6 nits to bright sunlight at about 108 nits, with cone vision active from about 10 nits upward.[6] High dynamic range (HDR) television standards also use much higher luminance levels than older systems. The ITU's report on HDR television describes the perceptual quantizer (PQ) signal as operating over the range from 10,000 cd/m2 down to less than 0.001 cd/m2, and compares it with the legacy ITU-R BT.1886 standard operating at a peak level of 100 cd/m2.[20]

Reality Labs researchers studied what luminance VR users prefer. Nathan Matsuda, Alexandre Chapiro, Yang Zhao, Clinton Smith, Romain Bachy and Douglas Lanman built an HDR VR headset able to exceed 20,000 nits of peak luminance, analyzed the luminance of an existing HDR panorama dataset, and ran a study of brightness preferences. They concluded that "current commercial VR headsets do not meet user preferences for display luminance, even for indoor scenes".[21] The prototype, called Starburst, was demonstrated at the SIGGRAPH 2022 conference in Vancouver. UploadVR described it as topping out at 20,000 nits and so heavy that the headsets had to be suspended from above. It was a research device built from off-the-shelf parts, not a product.[22]

Optical see-through AR and ambient light

In optical see-through AR, the virtual image is added to light from the real world, so its visibility depends on the ratio between the two rather than on the display luminance alone. Researchers measure this with the ambient contrast ratio (ACR), which compares the luminance seen through a lit pixel with that seen through an unlit pixel, after adding the ambient luminance reduced by the combiner's see-through transmittance to both.[5] Xiong and colleagues estimate ambient luminance at about 30 nits in a normal living room (about 100 lux), about 150 nits under typical office lighting, about 300 nits outdoors on an overcast day and about 3,000 nits on a sunny day.[5]

The same review gives a minimum ACR of 3:1 for recognizable images, 5:1 for adequate readability and 10:1 or more for outstanding readability. Ignoring optical losses, it estimates that an ACR of 10:1 on a sunny day needs a display brightness of at least 30,000 nits.[5] Hsiang and colleagues use a 3:1 target and estimate that a display needs at least 10,000 nits on a sunny day, again before optical losses. They add that methods that enlarge the eye box, such as exit pupil expansion, demand a much brighter panel.[6] The Xiong review argues that a light engine of about 10,000 nits is needed to deliver about 1,000 nits to the eye, enough for an ACR above 3:1, through a typical AR combiner with less than 10% optical efficiency. It also notes that continuously displaying an image brighter than 10,000 nits may shorten device lifetime considerably.[5]

Measurements on shipping headsets show the problem. Austin Erickson, Kangsoo Kim, Gerd Bruder and Gregory Welch measured illuminance through the Microsoft HoloLens and HoloLens 2 under environments from 0 to 20,000 lux. The HoloLens 2 outperformed its predecessor, but both performed best in low light, gave suboptimal results in the 100-1,000 lux range where most indoor work happens, and were practically unusable outdoors above 10,000 lux.[8]

Two ways around the problem are to raise display luminance and to darken the view of the world. The Xiong review names both: tunable dimmers that change the see-through transmittance, and brighter microdisplays with more efficient combiners.[5] The Magic Leap 2 pairs a display range of 20-2,000 nits with dynamic dimming that can change lens transmission from 22% to 0.3%, according to details that Magic Leap's vice president of optical engineering, Kevin Curtis, presented at SPIE Photonics West 2022, as reported by Road to VR.[23] The Meta Ray-Ban Display, announced in September 2025, has a 600 x 600 pixel display with a 20 degree field of view and a brightness range Road to VR reported as 30-5,000 nits.[24]

Representative values

The figures below come from different measurement points (panel, engine or eye) and different conditions, so they are not directly comparable.

Item Luminance (nits) Point in optical path Source
Starlight to bright sunlight, range of human vision about 10-6 to 108 Scene Hsiang et al. (2022)[6]
Living room / office / overcast day / sunny day about 30 / 150 / 300 / 3,000 Ambient scene Xiong et al. (2021)[5]
Typical VR headset about 150-200 Display Xiong et al. (2021)[5]
Meta Quest 2 about 100 Headset UploadVR (2022)[19]
Starburst research prototype more than 20,000 Headset Matsuda et al. (2022)[21]
Magic Leap 2 20-2,000 Headset Road to VR (2022)[23]
Meta Ray-Ban Display 30-5,000 Glasses Road to VR (2025)[24]
Xreal One 600 perceived; 5,000 panel peak Eye and panel Xreal[16]
Sony ECX350F OLED microdisplay 10,000 (100% duty) Panel Sony (2024)[18]
JBD Hummingbird I module 6,000 Through diffractive waveguide JBD (2025)[17]
JBD green MicroLED panel record 10,000,000 Panel JBD (2025)[17]

See also

References

  1. ↑ 1.0 1.1 1.2 "Candela per Square Metre". International Dictionary of Marine Aids to Navigation. IALA. https://www.iala.int/wiki/dictionary/index.php/Candela_per_Square_Metre. Retrieved 2026-10-11.
  2. ↑ 2.0 2.1 2.2 2.3 Consultative Committee for Photometry and Radiometry (2021-03-22). "Mise en pratique for the definition of the candela and associated derived units for photometric and radiometric quantities in the SI (SI Brochure, 9th edition (2019), Appendix 2, v1.02)". BIPM. https://www.bipm.org/utils/en/pdf/si-mep/SI-App2-candela.pdf. Retrieved 2026-10-11.
  3. ↑ 3.0 3.1 Russ Rowlett (2008). "Units: N". How Many? A Dictionary of Units of Measurement. University of North Carolina at Chapel Hill. https://www.ibiblio.org/units/dictN.html. Retrieved 2026-10-11.
  4. ↑ 4.0 4.1 Matthew S. Smith (2023-06-30). "Mojo Vision Rocks the AR World with Red MicroLEDs". IEEE Spectrum. https://spectrum.ieee.org/microled. Retrieved 2026-10-11.
  5. ↑ 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 5.11 5.12 Jianghao Xiong, En-Lin Hsiang, Ziqian He, Tao Zhan, Shin-Tson Wu (2021). "Augmented reality and virtual reality displays: emerging technologies and future perspectives". Light: Science & Applications, vol. 10, article 216. doi:10.1038/s41377-021-00658-8. https://doi.org/10.1038/s41377-021-00658-8. Retrieved 2026-10-11.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 En-Lin Hsiang, Zhiyong Yang, Qian Yang, Po-Cheng Lai, Chih-Lung Lin, Shin-Tson Wu (2022-11-09). "AR/VR light engines: perspectives and challenges". Advances in Optics and Photonics, vol. 14, no. 4, pp. 783-861. doi:10.1364/AOP.468066. https://doi.org/10.1364/AOP.468066. Retrieved 2026-10-11.
  7. ↑ 7.0 7.1 "luminance (17-21-050)". CIE e-ILV, International Lighting Vocabulary. International Commission on Illumination. https://cie.co.at/eilvterm/17-21-050. Retrieved 2026-10-11.
  8. ↑ 8.0 8.1 8.2 Austin Erickson, Kangsoo Kim, Gerd Bruder, Gregory F. Welch (2020-10-30). "Exploring the Limitations of Environment Lighting on Optical See-Through Head-Mounted Displays". Proceedings of the 2020 ACM Symposium on Spatial User Interaction (SUI '20), pp. 1-8. ACM. doi:10.1145/3385959.3418445. https://par.nsf.gov/servlets/purl/10275660. Retrieved 2026-10-11.
  9. ↑ "SI unit - candela". BIPM. Bureau International des Poids et Mesures. https://www.bipm.org/en/si-base-units/candela. Retrieved 2026-10-11.
  10. ↑ "brightness (17-22-059)". CIE e-ILV, International Lighting Vocabulary. International Commission on Illumination. https://cie.co.at/eilvterm/17-22-059. Retrieved 2026-10-11.
  11. ↑ 11.0 11.1 11.2 11.3 11.4 "NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically". NIST Special Publication 811. National Institute of Standards and Technology. https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8. Retrieved 2026-10-11.
  12. ↑ "IEC 63145-20-10:2019 Eyewear display - Part 20-10: Fundamental measurement methods - Optical properties". IEC Webstore. International Electrotechnical Commission. 2019-08-16. https://webstore.iec.ch/en/publication/62508. Retrieved 2026-10-11.
  13. ↑ Karl Guttag (2021-06-01). "Nreal Teardown: Part 1, Clones and Birdbath Basics". KGOnTech. https://kguttag.com/2021/06/01/nreal-teardown-part-1-clones-and-birdbath-basics/. Retrieved 2026-10-11.
  14. ↑ "Revolutionizing next-generation VR and MR displays with a novel pancake optics". EurekAlert!. Compuscript. 2024-02-06. https://www.eurekalert.org/news-releases/1033555. Retrieved 2026-10-11.
  15. ↑ "Lumus Unveils Next-Gen Waveguides for AR Glasses at CES 2026, Including its First Geometric Waveguide to Exceed 70 degree Field of View". PR Newswire. Lumus. 2026-01-06. https://www.prnewswire.com/news-releases/lumus-unveils-next-gen-waveguides-for-ar-glasses-at-ces-2026-including-its-first-geometric-waveguide-to-exceed-70-field-of-view-302653598.html. Retrieved 2026-10-11.
  16. ↑ 16.0 16.1 "XREAL One". XREAL US Shop. XREAL. https://us.shop.xreal.com/products/xreal-one. Retrieved 2026-10-11.
  17. ↑ 17.0 17.1 17.2 "JBD cemented its MicroLED leadership in 2024 through breakthrough technologies and expanded market presence". JBD News. Jade Bird Display. 2025-01-01. https://www.jb-display.com/newsdetails/73.html. Retrieved 2026-10-11.
  18. ↑ 18.0 18.1 "Sony Semiconductor Solutions to Release 0.44-Type Full HD OLED Microdisplay with Industry's Smallest Pixels and Highest Brightness". Sony Mediaroom. Sony Semiconductor Solutions. 2024-09-24. https://sony.mediaroom.com/2024-09-24-Sony-Semiconductor-Solutions-to-Release-0-44-Type-Full-HD-OLED-Microdisplay-with-Industrys-Smallest-Pixels-and-Highest-Brightness. Retrieved 2026-10-11.
  19. ↑ 19.0 19.1 Ian Hamilton (2022-06-23). "Meta Research Suggests High Brightness HDR Key To VR's Future". UploadVR. https://www.uploadvr.com/hdr-meta-research-vr-future/. Retrieved 2026-10-11.
  20. ↑ "Report ITU-R BT.2390-11: High dynamic range television for production and international programme exchange". ITU-R. International Telecommunication Union. 2023-03. https://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-BT.2390-11-2023-PDF-E.pdf. Retrieved 2026-10-11.
  21. ↑ 21.0 21.1 Nathan Matsuda, Alexandre Chapiro, Yang Zhao, Clinton Smith, Romain Bachy, Douglas Lanman (2022-11-29). "Realistic Luminance in VR". SIGGRAPH Asia 2022 Conference Papers, pp. 1-8. ACM. doi:10.1145/3550469.3555427. https://research.facebook.com/publications/realistic-luminance-in-vr. Retrieved 2026-10-11.
  22. ↑ Ian Hamilton (2022-08-22). "Starburst: Eyes-In With Meta's 20K Nit HDR Display Tech". UploadVR. https://uploadvr.com/starburst-hdr-demo/. Retrieved 2026-10-11.
  23. ↑ 23.0 23.1 Ben Lang (2022-01-27). "Tons of New Magic Leap 2 Details Shed Light on Dynamic Dimming & More". Road to VR. https://www.roadtovr.com/magic-leap-2-details-dynamic-dimming-kevin-curtis/. Retrieved 2026-10-11.
  24. ↑ 24.0 24.1 Scott Hayden (2025-09-17). "Meta Unveils Ray-Ban Smart Glasses with Display, Launching for $800 This Month". Road to VR. https://roadtovr.com/meta-ray-ban-smart-glasses-display-price-release-date-specs/. Retrieved 2026-10-11.
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