Luminance Converter
Convert surface luminance between SI, Lambert, and foot-Lambert units.
Converter guide
About Luminance Converter
Luminance describes light emitted or reflected from a surface in a given direction per apparent area. This converter translates between SI and legacy units such as candela per square meter and foot-lamberts, which appear in display, projection, and lighting references.
How to use this converter
- 1Enter the surface luminance value from the source or meter.
- 2Choose the current and target units, making sure the measurement is luminance rather than illuminance on a surface.
- 3Read the converted value and retain the viewing or measurement geometry associated with the original.
Conversion method and technical details
Candela per square meter is the SI luminance unit. A foot-lambert is a customary luminance unit; conversion applies fixed factors through a common base. Luminance differs from illuminance because it concerns directional light leaving or reflecting from a surface.
Worked real-world example
A projector specification in foot-lamberts can be converted to cd/m² to compare with an SI-based display reference, while keeping the original screen and viewing conditions in mind.
Common scenarios and use cases
Translate screen brightness, projection, signage, and photometric specifications between unit systems.
For a dependable comparison, confirm both unit labels, keep the original measurement with the converted value, and use the precision required by the task. The converter changes the representation of a value; it does not measure the item or decide which standard your project requires.
Important details and limitations
Luminance measurements depend on direction, surface reflectance, display settings, and instrument geometry. A converted value does not establish image quality, comfort, or compliance with a display standard.
Check the output unit as well as the number. If the result will be reused in another calculation, retain full precision where possible and round only at the end. For measurements governed by a technical specification, use the standard and tolerance required by that document.
Frequently asked questions
Is luminance the same as illuminance?
No. Luminance describes light from a surface in a direction; illuminance describes light arriving at a surface.
What is the SI luminance unit?
Candela per square meter, written cd/m².
Does a higher luminance always look better?
No. Viewing conditions, contrast, glare, content, and user preference also matter.
Why can the converted number look much larger or smaller?
Different units use different scales. A measurement can have a larger number in a smaller unit and still describe the same quantity. Check the source and target unit labels before comparing values.
How many decimal places should I keep?
Keep enough precision for the job and avoid rounding values between steps. Round the final displayed answer to match the specification, document, or measuring tool you are using.