Nits and cd/m² are the same luminance quantity — the harder part is understanding what was measured
Display listings often switch between “nits” and “cd/m²” as though they were different brightness scales. They are not. One nit is one candela per square meter. The number only becomes useful once you also know whether it describes a small HDR highlight, a full-screen level, a minimum, a typical value, or a peak under a particular test.
What cd/m² measures
The SI derived unit of luminance is the candela per square meter, written cd/m². NIST and the Bureau International des Poids et Mesures describe luminance in those units. Luminance is directional: it characterizes the light leaving or reflected from a surface toward a given direction rather than simply counting all light emitted in every direction.
That makes luminance a natural quantity for screens. When a monitor specification says 400 cd/m², it is describing the brightness of the display surface in a viewing direction under the stated or implied test conditions.
Where “nit” fits
“Nit” is a commonly used name for the same magnitude as one candela per square meter. NIST technical material explicitly identifies the candela per square meter as the SI luminance unit and notes that it is also known as the nit. Consumer display marketing usually prefers the shorter word because “500 nits” is easier to read than “500 cd/m².”
| Display claim | Equivalent luminance | Conversion needed? |
|---|---|---|
| 250 nits | 250 cd/m² | No — the numerical value is unchanged |
| 400 nits | 400 cd/m² | No |
| 600 cd/m² | 600 nits | No |
| 1,000 nits | 1,000 cd/m² | No |
The useful comparison is therefore not “nits versus cd/m².” The useful comparison is what kind of luminance result the number represents.
Nits are not lumens
Lumens measure luminous flux, which is a quantity of visible-light output. A screen's luminance is not the same measurement. Two objects can have the same total luminous flux while distributing that light over different areas or directions, so a lumen number does not translate directly into a monitor's nit value without geometry and directional information.
This is why projector specifications commonly emphasize lumens while monitors and televisions commonly emphasize luminance in nits or cd/m². The quantities answer different questions.
Nits are not lux either
Lux measures illuminance: luminous flux arriving on a surface per unit area. NIST lists the lux as the SI unit of illuminance and candela per square meter as the SI unit of luminance. A room-light meter measuring how much light falls on a desk is therefore measuring a different quantity from a display meter measuring the screen's luminance.
| Quantity | Typical unit | What it describes | Common consumer example |
|---|---|---|---|
| Luminance | cd/m², often called nits | Light from a surface in a given direction | Monitor or TV brightness |
| Illuminance | lux | Light arriving on a surface | Room or desk lighting |
| Luminous flux | lumens | Visible-light output across directions | Projector or lamp output |
A 1,000-nit peak does not necessarily mean 1,000 nits full-screen
This is the most important practical limitation. Displays can behave differently depending on how much of the screen is bright, how long the bright pattern is shown, thermal and power limits, local dimming behavior, and the image mode being used. A peak-luminance figure therefore needs test context.
VESA's DisplayHDR certification is useful evidence of this distinction. Its published performance criteria report luminance in cd/m² and separate a small center-patch test from full-screen flash and full-screen long-duration tests. The program does not treat one headline brightness number as a complete description of a display's luminance behavior.
If a product page says only “peak 1,000 nits,” you still need to know the measurement window, duration, image mode, and whether the claim describes a certified test or the manufacturer's own procedure. A bright HDR highlight and a bright full-screen web page are not automatically the same workload.
Peak, typical, minimum, and sustained are different claim types
Retail specifications often use qualifiers such as peak, typical, minimum, or sustained. Those words matter more than whether the unit is written as nit or cd/m². There is no safe rule that turns an unlabeled marketing value into a certified full-screen result.
| Wording | What it may describe | What to verify |
|---|---|---|
| Peak luminance | A highest value reached under a defined condition, often for a limited pattern or time | Window size, duration, mode, and test method |
| Typical luminance | A manufacturer-declared representative value | Manufacturer definition and whether a tolerance/minimum is also published |
| Minimum luminance | A lower guaranteed or required value under stated conditions | The exact condition and whether it is a product spec or certification threshold |
| Full-screen sustained | Luminance maintained with a large bright image for a longer interval | Duration, image pattern, thermal state, and image mode |
Why display area matters even though the unit already contains “per square meter”
The “per square meter” part of cd/m² defines the luminance unit; it does not mean every part of a real display must produce that luminance at the same time. A display can reach a high luminance on a small bright region while producing a lower value when the entire panel is white.
That is why a test report often specifies an area percentage or a particular test pattern. The unit stays cd/m² in both cases, but the display operating condition changes. This is an important distinction when comparing OLED, mini-LED LCD, conventional LCD, and other display architectures with different power and thermal behavior.
Does a higher nit number always mean a better display?
No. Higher available luminance can help in bright ambient light and can provide more headroom for HDR highlights, but luminance is only one display characteristic. Black level, contrast behavior, color gamut, color accuracy, tone mapping, viewing conditions, reflections, local dimming, panel uniformity, and sustained behavior also affect the result.
A display can therefore have a larger peak-luminance number while being a worse fit for a particular job. For HDR certification specifically, VESA's DisplayHDR tiers include more than luminance alone. See DisplayHDR 400, 600, 1000 and True Black for the separate brightness, black-level, color, and test-pattern requirements.
A practical brightness-spec checklist
- Treat nit and cd/m² as numerically identical. Do not waste time converting between them.
- Look for the qualifier. Is the number peak, typical, minimum, or sustained?
- Look for test area and duration. A small HDR window and a full-screen pattern can produce different results.
- Check the image mode. HDR, SDR, calibrated, vivid, and power-saving modes may not expose the same luminance behavior.
- Separate certification from a manufacturer claim. A DisplayHDR result follows the program's defined tests; an uncited product-page figure may use another method.
- Do not compare nits with lux or lumens as if they were the same quantity.
- Use luminance as one field in the decision, not the entire display verdict.
Example: two monitors both advertised as 600
Suppose one monitor is listed as “600 nits peak” with no test detail, while another carries a current DisplayHDR 600 certification. The two values have the same unit magnitude, but they do not contain the same amount of evidence. The certification ties the display to a defined set of luminance and other performance tests; the unlabeled peak claim tells you much less about full-screen or sustained behavior.
The right conclusion is not that the certified display must be better in every way. It is that the meaning of its brightness claim is more constrained by a published test framework.
Primary sources
- NIST — SP 330 Appendix 1, for luminance as candela per square meter, illuminance as lux, and luminous flux as lumen.
- NIST — Realization of related photometric units, for practical realization of luminance in candela per square meter.
- NIST/NBS Special Publication 480-16, for the explicit statement that the candela per square meter is also known as the nit.
- BIPM — CGPM Resolution 12 (1960), for the SI derived quantity table identifying luminance as cd/m².
- VESA Certified DisplayHDR — Performance Criteria, for current luminance tests reported in cd/m² and the separation of center-patch, full-screen flash, and full-screen long-duration behavior.
Bottom line
One nit equals one candela per square meter. The unit conversion is the easy part. The useful buying question is what test produced the number. Compare peak with peak, sustained with sustained, and certified criteria with the same certification framework whenever possible.