Enter the luminous intensity (in candelas, in the viewing direction) and the emitting area (m²) into the calculator. The calculator will estimate the luminance in candela per square meter (cd/m²). Note: cd/m² describes luminance (surface “brightness” in a direction), not illuminance on a surface (lux).
Candela Per Square Meter Formula
CPSM = I / A
Variables:
- CPSM is the candela per square meter (cd/m²), also called luminance (sometimes “nits,” where 1 nit = 1 cd/m²).
- I is the luminous intensity in candelas (cd) in the viewing direction.
- A is the emitting (projected) area (m²) of the source surface for that viewing direction (often approximated as the physical area when viewed head-on).
To estimate candela per square meter, divide the luminous intensity (in a specified direction) by the emitting/projected area in square meters.
How to Calculate Candela Per Square Meter?
The following steps outline how to calculate the Candela Per Square Meter.
- First, determine the luminous intensity (in candelas) in the viewing direction.
- Next, determine the emitting (projected) area (m²).
- Next, gather the formula from above = CPSM = I / A.
- Finally, calculate the candela per square meter (cd/m²).
- After inserting the variables and calculating the result, check your answer with the calculator above.
Example Problem :
Use the following variables as an example problem to test your knowledge.
luminous intensity (cd) = 91203
emitting area (m²) = 1123, so CPSM = 91203 / 1123 = 81.22 cd/m²
Frequently Asked Questions
What is a candela and how is it used in lighting?
A candela (cd) is the SI unit of luminous intensity, which describes how much light a source emits in a particular direction per unit solid angle. It is commonly used to describe directional output of light sources (for example, a spotlight beam). For total light output in all directions, luminous flux in lumens (lm) is typically used.
Why is measuring Candela Per Square Meter important in lighting design?
Candela per square meter (cd/m²) is a measure of luminance—the apparent brightness of an emitting or reflecting surface in a given direction (for example, a display, a luminaire diffuser, a wall, or pavement). In lighting design it is useful for evaluating perceived brightness, uniformity, and potential glare. If you need “light falling on a surface,” that is illuminance, measured in lux (lm/m²).
Can the Candela Per Square Meter value affect the mood or atmosphere of a room?
Yes. The luminance (cd/m²) of key surfaces in the field of view (such as walls, ceilings, fixtures, and screens) strongly influences perceived brightness, comfort, and glare, which can affect mood and atmosphere. (Illuminance in lux also matters for task visibility.)
How does the area influence the calculation of Candela Per Square Meter?
In this calculator, cd/m² is estimated as luminous intensity (cd) divided by emitting/projected area (m²). For a fixed luminous intensity in a given direction, using a larger emitting area results in a lower average luminance, and a smaller emitting area results in a higher average luminance.
