Luminance and Nits
A nit is one candela per square metre, a unit used to describe the luminance of displayed images.
1 nit = 1 candela per square metre (cd/m²). The unit expresses luminance: light leaving a surface in a specified direction, weighted for human vision.
The number is useful only when its object is identified:
| Stated number | Read it as |
|---|---|
| A patch at 500 nits | The intended or measured luminance of that patch |
| Mastering maximum of 1,000 nits | The mastering display's configured maximum |
| Television peak of 1,000 nits | A display result under stated test conditions |
| MaxFALL of 200 nits | A reported frame-average content-light bound |
Patch size makes a practical difference
A small 1,000-nit reflection and a large 1,000-nit field have the same local luminance, but ask the screen to illuminate different areas. The screen's power and thermal behavior can make the sustainable result depend on patch size and duration. A peak measurement therefore needs its test conditions beside the number.
Signal coordinates and light units are different
Video transfer functions establish the relationship between stored signal and light. With PQ, a normalized signal near 0.508 represents approximately 100 nits for neutral gray; doubling that signal would not double the nits. The PQ curve shows the nonlinear relationship.
HDR production guidance uses a 203-nit reference white under specified reference conditions, leaving space above ordinary white for highlights. Actual object placement is a grading decision.
During playback, tone mapping can change source light levels to fit the output. Keep the source request, metadata field, and measured screen output named separately when comparing an Emby session.