Nits and Luminance Explained

What does a screen rated at 300 nits really promise? It promises that every square metre of that glowing surface sends out 300 candelas of light toward your eyes. A movie theater spec may say the same thing in foot-lamberts, and a lighting plan may talk in lux. This guide shows how those numbers connect, and which ones never convert at all.

What Does One Nit Actually Measure?

One nit is one candela of light coming from each square metre of a surface. It measures luminance, which is how intense a surface looks from where you stand. The official SI name is the candela per square metre, written cd/m2.

The candela is the SI base unit for luminous intensity, the strength of light in one direction. Luminance spreads that intensity over the area you see. A small, fierce glow and a wide, gentle one can share the same candela total yet have very different nits.

This is why a phone and a large television can both claim a high nit rating. The number describes brightness per patch of screen, not the total light of the whole panel. Screen shape does not change it either, a separate topic covered in our guide to aspect ratio and screen shapes.

The name “nit” is informal but widely used by display makers. The NIST guide to the SI lists luminance simply as candela per square metre. Both labels point to exactly the same value, so 500 nits and 500 cd/m2 are identical.

How Do Nits Line Up Against Foot-Lamberts and Other Old Units?

Each older luminance unit equals a fixed number of nits, so conversion is one multiplication. NIST lists one foot-lambert as 3.426259 cd/m2, one lambert as 3,183.099 cd/m2, and one stilb as exactly 10,000 cd/m2.

Our converter uses its own example: turn 300 nits into foot-lamberts. Divide 300 by 3.426259 and you get 87.56, which rounds to 87.6 fL. Going the other way, 100 fL times 3.426259 gives about 342.6 nits.

For any pair of units, the luminance converter for nits, foot-lamberts and stilbs multiplies by the first unit’s nit value, then divides by the second. It rounds results to seven significant figures.

NIST also lists the candela per square inch at 1,550.003 nits. That unit is not in our converter, so multiply by hand when an older datasheet uses it.

Why Do Lambert Units Carry a Factor of Pi?

Lambert units describe a perfectly diffuse surface by the light it gives off, not by candelas per area. Turning that total into candelas means dividing by pi. That single step explains the untidy numbers.

A foot-lambert equals 1/pi candela per square foot. A square foot is 0.3048 squared, or 0.0929 square metres. Divide 1/pi by 0.0929 and you land on 3.4263 nits, which matches the NIST figure.

The same logic runs through the metric family. One lambert is 10,000/pi, or about 3,183 nits. One millilambert is a thousandth of that, about 3.183 nits. One apostilb is 1/pi, or about 0.3183 nits.

This detail matters when you check someone else’s math. A converted value that comes out perfectly round usually means the pi was dropped. Treating a foot-lambert as 3 nits, for example, puts a 300-nit screen at 100 fL instead of 87.6 fL.

Is a Lux the Same Thing as a Nit?

No. Lux measures illuminance, the light arriving on a surface, while nits measure luminance, the light leaving it toward your eye. NIST defines the lux as one lumen per square metre, a different unit from the candela per square metre.

Think of a desk lamp shining on paper. A light meter on the paper reads lux, because it catches the incoming light. A camera pointed at the paper responds to nits, because it sees the light bouncing back.

The two link only through the surface itself. For a perfectly diffuse surface, luminance equals illuminance times reflectance, divided by pi. Paper that reflects 80 percent of 500 lux shows about 127 nits. Dark card reflecting 20 percent shows about 32 nits under that same lamp.

So no single factor turns lux into nits. You always need the reflectance, and real surfaces are rarely perfectly diffuse. Treat the formula as a rough guide for matte surfaces, not for glossy or glowing ones.

The footcandle belongs on the lux side as well. NIST lists one footcandle as 10.76391 lux, so it measures arriving light, never nits.

What Brightness Numbers Show Up on Screens and in Cinemas?

Published reference values run from about 80 nits for a standard monitor target to about 2,500 nits for bright HDR displays. The figures below come from the references listed at the end of this article.

• The sRGB monitor specification targets 80 cd/m2, about 23.3 fL.
• Monitors calibrated for SDR broadcast or studio grading typically run at 100 cd/m2.
• Most consumer desktop LCDs reach 200 to 300 cd/m2.
• HDR displays range from around 400 to 2,500 cd/m2.

Cinema uses foot-lamberts. The film standard SMPTE 196M once recommended 16 fL with no film in the projector. Film peak white landed near 14 fL. Those equal about 54.8 and 48.0 nits. The current revision states 55 cd/m2, which matches the old 16 fL almost exactly.

What Should You Check Before Comparing Two Brightness Specs?

Confirm that both numbers describe luminance in the same unit and under similar conditions. A nit figure beside a foot-lambert figure needs conversion first. A lux or lumen figure is not luminance at all.

Lumens describe the total light a source sends out in every direction. A projector rated in lumens can look dim or bright depending on the screen size. The brightness you see on that screen is the luminance, in nits or foot-lamberts.

Watch the direction of the conversion too. Dividing when you should multiply turns 300 nits into about 1,028 fL instead of 87.6 fL. A quick sanity check helps: foot-lambert numbers are always smaller than the matching nit numbers.

Finally, keep brightness separate from energy use. A nit rating says nothing about electrical draw. For that side of a screen or lamp, see our guide on how to calculate power in watts.

FAQs About Nits and Luminance

Sources

This article explains luminance units for general education and does not rate or recommend any display. Unit factors follow NIST SP 811. Reviewed for accuracy by Prof. Dr. Khalil Mudassar, PhD. Last updated September 27, 2026.