Luminous Intensity Converter
Convert between luminous intensity units — candela (international), German and UK candle, decimal candle, pentane candle, Hefner candle, Carcel unit, bougie décimale, and lumen/steradian.
Results from this calculator are estimates provided for general informational purposes only, based on formulas, rates, and standards commonly accepted as of 2026. Figures may differ slightly from other calculators or professional sources due to rounding methods, differing assumptions, or regional regulations, and rules may change over time. Always consult a qualified professional — such as a financial advisor, healthcare provider, or other relevant specialist — before making decisions based on these results.
Result
1 cd = 1.1111111 HK
1 Candela (International) = 1.1111111 Hefner Candles
1 Hefner Candle = 0.9 Candela (International)
1 cd in every supported unit
What is a Luminous Intensity Converter?
Luminous intensity is one of the seven base physical quantities in the International System of Units (SI) — alongside length, mass, time, electric current, temperature, and amount of substance. It measures how much light-power a source radiates in a specific direction, weighted by how sensitive the human eye is to that light's wavelength, and its SI unit is the candela (cd). That's different from luminous flux, measured in lumens, which totals up the light a source emits in every direction at once, and different again from illuminance, measured in lux, which is how much of that light actually lands on a given surface area. A single LED can have a high candela rating in one narrow beam direction while emitting relatively few total lumens overall — which is exactly why intensity, flux, and illuminance are all reported separately on a good lighting spec sheet.
This converter is used whenever someone needs to compare a luminous intensity figure across unit systems or eras — reading a light bulb or LED spec sheet's candela rating, comparing flashlight or headlight beam-intensity ratings (often quoted in candela for "throw" distance), specifying stage and theatrical lighting fixtures, or translating historical photometric literature that used long-obsolete national "candle" standards into the modern SI candela. Every unit below is defined relative to the candela, so any two luminous intensity units — modern or historical — can be converted directly and consistently.
Conversion chart: Candela (International) to Hefner Candles
Conversion table
| Candela (International) (cd) | Hefner Candle (HK) |
|---|---|
| 0.01 cd | 0.011111111 HK |
| 0.1 cd | 0.11111111 HK |
| 1 cd | 1.1111111 HK |
| 2 cd | 2.2222222 HK |
| 3 cd | 3.3333333 HK |
| 5 cd | 5.5555556 HK |
| 10 cd | 11.111111 HK |
| 20 cd | 22.222222 HK |
| 50 cd | 55.555556 HK |
| 100 cd | 111.11111 HK |
| 1000 cd | 1111.1111 HK |
Supported Units
| Unit | Symbol | In Candela |
|---|---|---|
| Candela (International) | cd | 1 cd |
| Candle (German) | c (German) | 1.0526316 cd |
| Candle (UK) | c (UK) | 1.0416667 cd |
| Decimal Candle | dec. candle | 1 cd |
| Candle (Pentane) | candle (pentane) | 1 cd |
| Pentane Candle (10 Candle Power) | 10cp candle | 10 cd |
| Hefner Candle | HK | 0.9 cd |
| Carcel Unit | carcel | 9.61 cd |
| Bougie Décimale | bougie déc. | 1 cd |
| Lumen/Steradian | lm/sr | 1 cd |
About These Parameters
- Value
- The luminous intensity value you want to convert, expressed in the "From" unit. Accepts decimals, and can represent anything from a small LED indicator's fraction of a candela to a searchlight's rating of thousands of candela.
- From Unit
- The unit your input value is currently measured in — a modern spec sheet's candela (cd) rating, or a historical figure quoted in Hefner candles, Carcel units, or another older photometric standard.
- To Unit
- The unit you want the result converted into. Use the swap button to flip From and To instantly, which is handy when translating an older historical figure into the modern candela or vice versa.
How Luminous Intensity Conversion Works
The Formula
Every unit here is defined by a fixed multiplier relative to the candela (international). To convert a value from one unit to another:
result = value × (factor of "From" unit ÷ factor of "To" unit)
For Candela (International) → Hefner Candle: multiply by 1.1111111. For example, 1 cd × 1.1111111 = 1.1111111 HK.
From Candles to Candela
Before 1979, "how bright is this light" had no single international answer — it depended on which country's reference flame you were comparing against. Germany used the Hefner candle, a small lamp burning amyl acetate; France used first the oil-fed Carcel lamp and later the metric bougie décimale; Britain used its own standardized spermaceti candle; and photometry labs more broadly relied on pentane lamps for their reproducibility. Each of these was a literal physical object, burned under tightly controlled conditions, that labs had to maintain and periodically recalibrate against each other. In 1979 the International Committee for Weights and Measures replaced all of them with a single physics-based definition: the candela is now defined as the intensity of a source emitting monochromatic 540 THz radiation at a radiant intensity of 1/683 watt per steradian — no flame, lamp, or physical artifact required, and reproducible identically in any properly equipped laboratory on Earth.
Why So Many Historical "Candle" Units?
Before international standards bodies coordinated photometry, each industrializing nation needed its own reproducible light-intensity reference for gas lighting, lighthouses, and early electric lamps — and building one from scratch, tuned to locally available materials like German amyl acetate lamps or French colza oil, was more practical than importing another country's exact standard. That's why this page carries so many near-but-not-quite-equal "candle" units: they were all solving the same problem independently, in different countries, within a few decades of each other, before the candela unified them into a single SI-defined quantity.
Example
A luminous intensity of 1 cd equals 1.1111111 HK. For scale, a single common candle flame is close to 1 candela, a typical household LED bulb might be rated around 100-200 candela in its brightest direction, and a car headlight's high beam can exceed 100,000 candela in its most concentrated beam.
Frequently Asked Questions
What's the difference between candela, lumens, and lux?
Candela measures luminous intensity — how bright a source is in one specific direction. Lumens measure total luminous flux — the light emitted in every direction combined. Lux measures illuminance — how much light actually reaches a given surface area. A narrow, focused beam can have very high candela but relatively modest total lumens, while a wide floodlight can have high lumens spread across a much lower candela in any single direction.
Is the international candle the same as the modern candela?
Yes — the international candle (candela, international) is the base unit this whole converter is built on, with a factor of exactly 1. It's the direct predecessor terminology to today's SI candela and the two are used interchangeably in most modern contexts.
Why is the Hefner candle slightly less than one candela?
The Hefner candle was defined by a physical amyl-acetate lamp built to German specifications in 1884, decades before the candela was redefined using monochromatic radiation. When photometrists later measured the Hefner lamp's output against the international candle standard, it came out to about 0.9 candela — a real, measured physical relationship rather than a designed round number.
Why does lumen/steradian equal candela exactly?
Because that's literally how the candela is defined mathematically — one candela is defined as one lumen of luminous flux per steradian of solid angle. Lumen/steradian isn't a different physical quantity being converted to candela, it's the same quantity written out in its base SI derived-unit form, so the conversion factor between them is exactly 1.