Inside this guide
A display listing gives nits, while a projection document uses foot-lamberts. Both describe luminance, but the unit conversion is not the whole comparison. A small peak test window, a full-screen image and sustained output can produce different ratings on the same device.
One nit is one cd/m². Luminance depends on direction and projected surface area, and perceived brightness also depends on surroundings and adaptation. Illuminance in lux is a different quantity. Ambient light, reflections, image content and measurement geometry should remain in the record when comparing displays or surfaces.
Display comparisons need the same test pattern
A screen measurement of 250 cd/m² is 250 nits. The alternative name does not change the value. Expressing it in foot-lamberts gives about 72.9665 fL, but that equivalent retains the same viewing direction and test conditions.
A small-window peak rating can be higher than full-field sustained luminance. Comparing those different test conditions as though they were identical can make a specification table misleading. Include window size, duration, display mode and ambient conditions when they are available. A prefix conversion cannot recreate those missing details.
Perceived brightness also depends on contrast, reflections and visual adaptation. A high numerical luminance does not by itself rank a display's colour accuracy or suitability for a room. Illuminance in lux describes light arriving at a surface, so it cannot be translated directly into nits without an appropriate optical and surface model. Use this converter for a supplied luminance, and reserve display-quality conclusions for comparable measurements.
What the units preserve
Luminance describes visible light emitted or reflected in a specified direction per projected area and solid angle. Convert cd/m², cd/cm², foot-lamberts and lamberts for supplied measurements. It is often used for screens and surfaces; perceived brightness also depends on surroundings and visual adaptation.
A nit is exactly one cd/m². Foot-lamberts and lamberts use definitions involving area and π, so their displayed decimal equivalents can be rounded. Luminance is different from illuminance in lux. Converting between those physical quantities requires additional surface or optical information, not simply a prefix.
Practical checkpoint: Align the test window, duration and viewing conditions before treating converted luminance numbers as comparable performance.
Work through the numbers
Start with 300 cd/m², supplied in candelas/square metre (nits), and express the same quantity in foot-lamberts. The Luminance Converter gives 87.559052388 fL. The arithmetic below uses the converter's underlying factors, while the displayed values are rounded for reading.
Calculation: 300 × 1 ÷ 3.42625909964 = 87.559052388 fL.
Keep any reporting or purchasing rule separate from the arithmetic. The mathematical equivalent appears before a chosen rounding rule or practical margin.
Change one input at a time
The factor ratio is fixed for this pair of units. Half the input produces half the equivalent output, and twice the input produces twice the output. That relationship describes the numerical conversion of luminance, rather than a new prediction about the physical system. Only the input magnitude changes here. The source unit, destination unit and interpretation stay fixed, so the table is a controlled arithmetic comparison rather than a collection of unrelated examples.
| Controlled case | Original value | Equivalent value |
|---|---|---|
| Half the starting input | 150 cd/m² | 43.779526194 fL |
| Starting example | 300 cd/m² | 87.559052388 fL |
| Twice the starting input | 600 cd/m² | 175.118104776 fL |
The starting case is 300 cd/m² → 87.559052388 fL. Converting the unrounded result back gives 300 cd/m². A reverse calculation is useful for catching a reversed factor or a mistyped prefix. It cannot prove that the original observation was accurate or that the selected physical quantity was appropriate.
Useful equivalents for this example
Each row below expresses the same starting quantity, 300 cd/m². These are equivalent representations, not additional measured observations. Read the full unit symbol: its prefix, exponent and denominator determine the factor. A larger numerical display can simply mean that the destination unit is smaller.
| Destination convention | Unit symbol | Equivalent of the starting value |
|---|---|---|
| Candelas/square metre (nits) | cd/m² | 300 |
| Candelas/square centimetre | cd/cm² | 0.03 |
| Foot-lamberts | fL | 87.559052388 |
| Lamberts | L | 0.0942477796077 |
Use the convention required by the document or instrument. Keep the original unit beside the equivalent when the calculation needs to be traced.
A practical checking workflow
Before entering a figure, identify the quantity and collect the context that makes it interpretable. For this topic, use these specific checks:
- Retain the viewing direction and measurement geometry.
- Check whether a screen rating is peak, full-field or sustained luminance.
- Keep ambient-light and test-pattern conditions with a display measurement.
Then enter the original value in the Luminance Converter and select both unit labels deliberately. Inspect the output magnitude against the worked example rather than trusting a familiar-looking prefix. Copy the unit with the result so that a plain number is not separated from its meaning. If several values will be compared, use a consistent convention for all of them.
For a display comparison, convert like-for-like luminance readings and keep their peak or sustained labels. Retain the test window size and ambient conditions where available.
Digital and electrical specifications often depend on conventions that a prefix cannot describe. Decimal and binary storage units, bit and byte rates, average and peak electrical readings, and nominal versus usable capacity should stay distinguishable. A comparable display is useful only after the quantities themselves have been aligned.
A manufacturer's test conditions can explain a difference more effectively than an extra decimal place. Retain voltage, operating mode, waveform statistic, bandwidth or measurement geometry when it is relevant to the topic. An advertised maximum should not quietly become a sustained measured result. If a model needs another variable, such as time or voltage, show that variable explicitly instead of implying that it was contained in the unit conversion.
Common mistakes and how to resolve them
The following problems arise from interpretation rather than arithmetic alone. A correct factor can preserve an incorrect assumption, so address the cause before accepting the output.
| Mistake to look for | A more useful action |
|---|---|
| Converting lux as though it were nits | Illuminance and luminance describe different light measurements. |
| Comparing peak and full-screen ratings as equivalent | Align the test pattern and measurement conditions before comparing. |
If the source is ambiguous, identify the assumption and check it against the original specification. Regulated work should follow its specified measurement and verification procedure.
Pros and cons of a unit-first comparison
| Part of the comparison | Pros: what it helps with | Cons: what still needs checking |
|---|---|---|
| Unit alignment | 300 cd/m² and 87.559052388 fL can be compared as one quantity. | Nits and cd/m² are the same unit. Perceived brightness also depends on surroundings and display content. |
| A practical decision | Align the test window, duration and viewing conditions before treating converted luminance numbers as comparable performance. | Illuminance and luminance describe different light measurements. |
| A repeatable calculation | The controlled examples show how the output responds while the unit pair stays fixed. | Retain the viewing direction and measurement geometry. |
The benefit is a transparent unit relationship. The limit is that the source measurement and the physical model still determine whether the comparison answers the intended question.
Precision, uncertainty and reporting
Keep the distinction between an exact unit definition and an uncertain measurement. A factor can be defined exactly while the input comes from a limited instrument or a rounded specification. The converter carries up to twelve significant digits for a readable result; that display is a calculation format rather than a claim of twelve-digit measurement accuracy.
For a fixed-factor relationship, an input interval maps through the same factor ratio. For an offset relationship, apply the mapping to the relevant endpoints. For a reciprocal relationship, check both endpoints carefully because the order reverses. Report uncertainty using the source's meaning rather than inventing an interval from the number of decimal places shown on screen.
Round at the final reporting step, after any further calculation that needs the value. If rounding could affect a threshold, whole-pack count or specification comparison, retain the unrounded result and state the rule used for the decision. A result very close to a boundary deserves a check of the original measurement, not just another decimal in the display.
Frequently asked questions
Are nits and cd/m² the same?
Yes. Nit is a commonly used name for the candela per square metre. Their numerical values are identical; neither is a direct measure of perceived brightness in every setting.
Does higher luminance always mean a better display?
No. Contrast, colour, reflections, viewing conditions and sustained performance also matter. This converter changes units rather than ranking display quality.
What does the worked example establish?
It establishes the arithmetic under the stated unit conventions. 250 cd/m² = 250 nits ≈ 72.9665 foot-lamberts. The illustrative inputs are not measurements of your equipment, material or project. Replace them with a suitable record and preserve the conditions before applying the result.
Conclusion: keep the meaning with the number
Align the test window, duration and viewing conditions before treating converted luminance numbers as comparable performance. The numerical example converts 300 cd/m² into 87.559052388 fL. Its value comes from making the unit relationship visible while keeping the physical interpretation intact. Use the Luminance Converter for the calculation, then apply the task's measurement conditions and decision rules separately.