Luminous Intensity Converter
Convert luminous intensity between candela, millicandela, spherical candela, Hefner candle, and Violle. Enter a value and select the units to convert from and to.
Convert Luminous Intensity Between Units
Luminous Intensity Conversion Formula
Where:
- \(I_{\mathrm{from}}\) — luminous intensity entered in the selected From unit
- \(I_{\mathrm{to}}\) — luminous intensity in the selected To unit
- \(f_{\mathrm{from}}\) and \(f_{\mathrm{to}}\) — the number of candelas represented by one of each selected unit
The calculator first expresses the entered value in candelas, then divides by the candela value of the target unit. Both factors must use the same candela reference.
Luminous Intensity – Calculation Example
Example: convert the default value of 100 candela (cd) to millicandela (mcd). One candela equals 1,000 millicandela, so the factors are 1 cd per cd and 0.001 cd per mcd.
\[ I_{\mathrm{to}}=100\,\mathrm{cd}\times\frac{1\,\mathrm{cd/cd}}{0.001\,\mathrm{cd/mcd}}=100{,}000\,\mathrm{mcd} \]
Result: 100 cd = 100,000 mcd.
How to use the calculator
- Enter a nonnegative number in Luminous intensity value. Use the value as stated in a lamp, LED, or other light-source specification.
- Choose its current unit in From unit.
- Choose the unit you need in To unit.
- Read Converted Luminous Intensity. The result includes the abbreviation of the selected target unit.
The default settings convert 100 cd to mcd. If you select the same unit in both menus, the numerical value remains unchanged. The displayed result is rounded to up to six decimal places, so very small converted values may appear as zero.
What luminous intensity means
Luminous intensity describes how much visible light a source sends in a particular direction per unit of solid angle. Its SI unit is the candela (cd). Because it is directional, a source can have different intensity values at different viewing angles. For example, a focused beam may have a high intensity along its centerline without emitting the same amount of light in every direction.
A conversion changes only the unit used to report an intensity. It does not change the direction being measured or provide a complete picture of the source’s light output. When comparing two specifications, check whether they refer to the same measurement direction. A peak intensity and an average intensity over a range of directions may describe the same product but answer different questions.
Luminous intensity is not the same as luminous flux, illuminance, or luminance. Luminous flux, measured in lumens, describes light output across directions; illuminance describes light arriving on a surface; and luminance describes the apparent brightness of a surface in a direction. If you are working with light on a surface, use the Light Illumination converter. For surface luminance units, use the Light Luminance converter.
Unit factors and practical limits
The converter uses the following factors. Each factor is the number of candelas assigned to one unit in this calculator:
| Unit | Abbreviation | Candelas per unit |
|---|---|---|
| Candela | cd | 1 |
| Millicandela | mcd | 0.001 |
| Spherical candela | scd | 1.0187 (approximate) |
| Hefner candle | hk | 0.903 |
| Violle | vi | 19.22 (approximate) |
The historical-unit factors, particularly those for spherical candela and Violle, are approximate values used by this calculator. Check the definition and conversion factor required by your source or standard before using a historical-unit result in a technical document. Candlepower (cp) and candela per steradian (cd/sr) are not selectable units here; do not treat them as alternative labels for the units in the menus.
Unit conversion alone cannot determine beam angle, total lumens, or brightness at a surface. Those quantities need additional information about how light is distributed or how far the surface is from the source. If you have a luminous-flux value and need to compare lumens with electrical watts under specified assumptions, see the Lumens to Watts calculator.
Frequently Asked Questions
How can I convert luminous intensity by hand?
Convert the starting value to candelas, then divide by the number of candelas in one target unit. For example, 5 Hefner candles equal \(5\times0.903=4.515\) cd. To express that in Violle, divide by 19.22, giving approximately 0.235 vi. Historical-unit factors can vary by reference, so use the factors specified by your source when precision matters.
What is a good luminous intensity for an LED?
There is no single good value: it depends on the LED’s purpose and viewing angle. A narrow-beam LED can have a high candela rating while lighting only a small area; a wide-angle LED may have a lower rating yet spread light more broadly. Compare specifications measured at similar angles and operating currents, and consider luminous flux when overall light output matters.
Can I convert candelas to lumens?
Yes, but only if you know how the light is distributed. For uniform intensity over a known solid angle, luminous flux is \(\Phi=I\Omega\), where \(I\) is in candelas, \(\Omega\) is in steradians, and \(\Phi\) is in lumens. A single peak candela rating is not enough to find total lumens for a real beam.
How do I convert candelas to lux at a given distance?
For a point-like source shining directly onto a surface, illuminance is approximately \(E=I/r^2\), where \(E\) is in lux, \(I\) is the intensity toward the surface in candelas, and \(r\) is the distance in metres. For example, 20 cd at 2 m gives about 5 lux. This approximation assumes the surface faces the light directly and ignores obstructions.
Why might a spherical candela conversion differ from another source?
Spherical candela is a historical unit whose quoted conversion can depend on the reference used. This converter assigns it approximately 1.0187 cd. It is not the same as multiplying a candela value by \(4\pi\): that operation gives lumens only for a source with uniform intensity in every direction. Check the source’s definition before comparing historical measurements.
Why does a small converted value show as zero?
The displayed answer is rounded to at most six decimal places. A positive result smaller than the displayed precision can therefore appear as zero even though its unrounded value is not zero. For a more useful figure, convert to a smaller unit when available, or calculate with the unit factors separately if you need additional decimal places.
Is candlepower the same as candela?
Candlepower is an older term often used informally for luminous intensity, and some modern specifications treat one candlepower as one candela. Historical uses were not always identical, however, so the term alone does not establish an exact conversion. Check the definition used in the specification rather than entering a candlepower figure as candelas without verification.
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