Luminous Intensity Converter
Print pageAll Equivalents Reference Table
| Unit | Equivalent Value |
|---|
Luminous Intensity (also known as Directional Light Power Density, Angular Luminous Flux Rate, or Photometric Candle Power, symbolized by Iv or I) measures the wavelength-weighted optical power emitted by a light source in a specific direction per unit solid angle, evaluated according to the standard human eye V(λ) photopic luminosity function (Iv = dΦv ÷ dΩ, where Φv is luminous flux in lumens and dΩ is solid angle in steradians). Across automotive LED headlight beam pattern compliance, marine navigation lighthouse signaling ranges, architectural spotlight beam angles, stage lighting design, optical fiber laser emission, and historical photometric candle standards, luminous intensity is categorized across three major optical unit families: International System of Units (SI fundamental base metric: Candela / cd, Lumen per Steradian / lm/sr, Candle (International) / c, Bougie Decimale, Decimal Candle), Historical Fuel Lamp Standards (Hefner Candle / HK / Hefnerkerze, Carcel Unit, Pentane Candle, 10-Candlepower Pentane Lamp), and Regional Imperial Candle metrics (Candle (German), Candle (UK) / Parliamentary Standard Candle).
Our free online Luminous Intensity Converter provides instant, high-precision conversions across all SI fundamental candela, CGS/imperial candlepower, and historical photometric lamp units:
- Candela to Lumen per Steradian [Exact SI 1:1 Base Identity]:
1 Candela (cd) = 1.0 lm/sr = 1.0 Candle (International) [c] = 1.0 Bougie Decimale = 1.0 Decimal Candle. - Hefner Candle (HK) to Candela [German Historic Standard]: Multiply HK by
0.900(1 HK = 0.900 cd = 0.900 lm/sr ⇒ 1 cd = 1.11111 HK). - Carcel Unit to Candela [French Colza Oil Standard]: Multiply Carcel by
9.610(1 Carcel = 9.610 cd = 9.610 lm/sr = 10.6778 HK). - German Candle to Candela & International Candle: Multiply German Candle by
1.05263158(1 c (German) = 1.05263 cd = 1.05263 lm/sr). - UK Parliamentary Candle to Candela: Multiply UK Candle by
1.04166667(1 c (UK) = 1.04167 cd = 1.04167 lm/sr). - 10-Candlepower Pentane Lamp to Candela: Multiply by
10.0(1 Pentane 10 c.p. = 10.0 cd = 10.0 lm/sr = 11.1111 HK).
Master Luminous Intensity Conversion Table
The table below displays exact mathematical conversion relationships, SI Candela (cd) multipliers, and Hefner Candle (HK) equivalents relative to 1 Candela (1 cd = 1 lm/sr = 1.11111 HK):
| Luminous Intensity Unit Name | Symbol | Exact Value in Candela (cd) | Lumen/Steradian & Hefner Candle Equivalent | Domain & Technical Application Standard |
|---|---|---|---|---|
| 1 Candela (Base SI Unit) | cd |
1.0 cd (Base SI Unit) |
1.0 lm/sr (1.11111 HK / 1.0 Candle (Int) / 0.104058 Carcel) |
SI Fundamental Base Unit of Luminous Intensity |
| 1 Lumen per Steradian | lm/sr |
1.0 cd |
1.0 lm/sr (100% mathematically equal to 1.0 cd) |
Derived Physical Definition of Directional Light Intensity |
| 1 Candle (International) | c, c.p. |
1.0 cd |
1.0 cd (1.11111 HK / 1.0 Bougie Decimale) |
International Photometry Standard (Adopted 1921) |
| 1 Hefner Candle (Hefnerkerze) | HK |
0.900 cd |
0.900 lm/sr (0.900 Candle (Int) / 0.093652 Carcel) |
German & Austrian Historic Standard Lamp Unit |
| 1 Carcel Unit | carcel |
9.610 cd |
9.610 lm/sr (10.6778 HK / 9.610 Candle (Int)) | French Colza Oil Burner Historic Standard Unit |
| 1 German Candle | c (German) |
1.052632 cd |
1.05263 lm/sr (1.16959 HK / 1.05263 c) | Historic Paraffin Candle Standard in Germany |
| 1 Pentane Candle (10 c.p.) | pentane (10 c.p.) |
10.0 cd |
10.0 lm/sr (11.1111 HK / 1.04058 Carcel) | Vernon Harcourt Pentane Standard Gas Lamp Unit |
Step-by-Step Automotive LED Headlight Intensity Calculation Example
To convert an automotive high-beam LED headlight array emitting a directional intensity of 65,000 Candelas (65,000 cd or 65 kcd) into Lumens per Steradian (lm/sr), Hefner Candles (HK), and total output in lumens for a narrow 15-degree spotlight beam cone (solid angle Ω = 0.054 steradians):
Step 1 (SI lm/sr Conversion): Iv = 65,000 cd × 1.0 = 65,000 Lumens per Steradian (lm/sr)
Step 2 (Hefner Candle HK Conversion): Iv = 65,000 cd × 1.11111 = 72,222.2 Hefner Candles (HK)
Step 3 (Spotlight Beam Total Lumens Calculation): Φv = Iv · Ω = 65,000 lm/sr × 0.054 sr = 3,510 Lumens
Thus, the 65 kcd LED headlight projects a directional intensity of 65,000 lm/sr (72,222 HK) and generates a total beam flux of 3,510 Lumens.
Real-World Light Source Luminous Intensity Benchmarks
Below is a comparative reference chart showing directional luminous intensity values (Iv) across everyday candles, light bulbs, headlights, and marine navigation lighthouses:
| Light Source / Illumination Device | Luminous Intensity in Candelas (cd) | lm/sr & Hefner Equivalent (lm/sr / HK) | Optical Photometry & Lighting Engineering Context |
|---|---|---|---|
| Standard Paraffin Wax Candle Flame | 1.0 cd (1.0 Candle) | 1.0 lm/sr (1.111 HK) | Historical reference baseline for 1 candlepower |
| 10-Watt Household LED Bulb (800 Lumens Omnidirectional) | 65.0 – 70.0 cd | 65.0 – 70.0 lm/sr (72.2 – 77.8 HK) | Uniform omnidirectional household room lighting |
| 100-Watt Incandescent Light Bulb (1,700 Lumens) | 135.0 cd (135.0 lm/sr) | 135.0 lm/sr (150.0 HK) | Classic tungsten wire filament omnidirectional emission |
| Automotive LED High-Beam Headlight Array | 40,000.0 – 100,000.0 cd (40 – 100 kcd) | 40,000 – 100,000 lm/sr (44.4k – 111.1k HK) | Focused long-range road illumination spot beam |
| Commercial Marine Navigation Lighthouse (Creac’h, France) | 500,000,000.0 cd (500 Megacandelas / Mcd) | 500.0 Mlm/sr (555.5 MHK) | Extreme ocean navigation signaling beam visible over 30 miles |
| Military Anti-Aircraft High-Power Searchlight | 1.0 × 109 cd (1 Gigacandela / Gcd) | 1.0 × 109 lm/sr (1.111 GHK) | Collimated carbon-arc searchlight beam piercing night sky |
History & Physics: 1890 Hefner Lamp vs 1979 CGPM SI Candela Definition
1890 Friedrich von Hefner-Alteneck & The Hefnerkerze (HK)
In 1890, German electrical engineer Friedrich von Hefner-Alteneck developed the Hefner Lamp, which burned pure amyl acetate with a precise 40 mm flame height. The lamp produced the Hefnerkerze (HK), which became the official photometric standard in Germany, Austria, and Scandinavia. In 1948, international standardization established that 1 HK = 0.900 Candela (cd).
1979 CGPM 16th Conference Definition of the SI Candela Base Unit
In 1979, the 16th General Conference on Weights and Measures (CGPM) redefined the SI base unit Candela (cd) strictly in terms of monochromatic physical radiation: “The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 Hertz (555 nm green light peak human eye sensitivity) and that has a radiant intensity in that direction of 1/683 watt per steradian.”
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Frequently Asked Questions (FAQ)
Is 1 Candela equal to 1 Lumen per Steradian?
Yes, 1 Candela (cd) is 100% mathematically equal to 1 Lumen per Steradian (1 lm/sr). Both units measure the exact same directional light power rate per solid angle.
How do you convert Hefner Candles (HK) to Candelas (cd)?
To convert German Hefner Candles (HK) to Candelas (cd), multiply HK by 0.900. For example, 100 HK × 0.900 = 90.0 Candelas (cd).
What is the difference between Lumens (lm) and Candelas (cd)?
Lumens (lm) measure the total overall light output emitted by a bulb in all directions. Candelas (cd) measure the directional intensity focused in a specific angle: Candela = Total Lumens ÷ Solid Angle (steradians).
Why was 555 nanometers chosen for the SI Candela definition?
Light at 555 nanometers (green light) corresponds to the absolute peak spectral sensitivity of human eye cone photoreceptors (photopic V(λ) curve). At 555 nm, 1 Watt of radiant optical power generates exactly 683 Lumens of light.