Illumination Converter
Print pageAll Equivalents Reference Table
| Unit | Equivalent Value |
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Photometric Illuminance (also known as Illumination Level, Incident Light Flux Density, or Surface Light Intensity Rate, symbolized by Ev or E) measures the total luminous flux incident per unit surface area (Ev = dΦv ÷ dA, where Φv is luminous flux in lumens and dA is illuminated surface area in square meters or square feet). Across commercial office building lighting design (OSHA and CIBSE compliance), indoor agricultural greenhouse PAR lighting, surgical operating room illumination, film set cinematography exposure, solar photovoltaic panel irradiance evaluation, and ecological nocturnal light pollution tracking, illuminance is categorized across four major optical unit families: International System of Units (SI metric fundamental: Lux / lx, Lumen per Square Meter / lm/m2, Meter-Candle / m·c, Candela Steradian per Sq. Meter), Imperial US/UK Architectural metrics (Foot-Candle / ft·c / fc, Lumen per Square Foot / lm/ft2, Flame), CGS High-Intensity standards (Phot / ph, Lumen per Square Centimeter / lm/cm2, Centimeter-Candle / cm·c), and Low-Light Astronomical metrics (Nox).
Our free online Illumination Converter provides instant, high-precision conversions across all SI metric, US imperial foot-candle, CGS phot, and architectural lighting illuminance units:
- Foot-Candle to Lux [US Architectural Lighting Standard]: Multiply fc by
10.7639104(1 foot-candle = 10.7639 Lux = 10.7639 lm/m2 ⇒ 1 Lux = 0.09290304 fc). - Phot to Lux & Foot-Candles [CGS Metric Standard]: Multiply phot by
10,000.0(1 phot = 10,000.0 Lux = 10,000.0 lm/m2 = 929.0304 foot-candles = 1.0 lm/cm2). - Lux to Lumen per Square Meter [Exact SI 1:1 Identity]:
1 Lux (lx) = 1.0 lm/m2 = 1.0 Meter-Candle (m·c) = 1.0 cd·sr/m2. - Flame to Lux & Foot-Candles: Multiply flame by
43.055642(1 flame = 43.0556 Lux = 4.0 foot-candles = 43.0556 lm/m2). - Nox to Lux [Low-Light Night Sky Metric]: Multiply nox by
0.001(1 nox = 0.001 Lux = 1.0 Millilux mlx = 0.0000929 fc). - Watt per Sq. Centimeter (at 555 nm) to Lux: Multiply by
6,830,000.0(1 W/cm2 at 555 nm = 6.83 × 106 Lux).
Master Photometric Illuminance Conversion Table
The table below displays exact mathematical conversion relationships, SI Lux (lx) multipliers, and Foot-Candle (fc) equivalents relative to 1 Lux (1 lx = 1 lm/m2 = 0.092903 fc):
| Illuminance Unit Name | Symbol | Exact Value in Lux (lx) | Foot-Candle (fc) & Phot Equivalent | Domain & Technical Application Standard |
|---|---|---|---|---|
| 1 Lux (Base SI Unit) | lx, lm/m2 |
1.0 lx (Base SI Unit) |
0.092903 fc (0.0001 phot / 1.0 m·c / 1,000 nox) |
SI Fundamental Unit of Surface Illuminance |
| 1 Foot-Candle | fc, ft·c, lm/ft2 |
10.7639104 lx |
1.0 fc (0.001076 phot / 10.7639 lm/m2) |
US Architectural Lighting & Building Code Standard |
| 1 Phot | ph, lm/cm2 |
10,000.0 lx |
929.030 fc (1.0 phot / 10,000 lm/m2 / 1.0 cm·c) |
CGS High-Intensity Solar & Optical Physics Unit |
| 1 Flame | flame |
43.055642 lx |
4.0 fc (0.004306 phot / 43.0556 lm/m2) | Traditional Gas Burner & Open Flame Illumination |
| 1 Meter-Candle | m·c |
1.0 lx |
0.092903 fc (100% mathematically equal to 1.0 Lux) | Historical Metric Distance Illumination Benchmark |
| 1 Centimeter-Candle | cm·c |
10,000.0 lx |
929.030 fc (1.0 phot / 10,000 lm/m2) | CGS Short-Range Point Source Illumination Unit |
| 1 Nox | nox |
0.001 lx |
0.0000929 fc (0.001 Lux / 1.0 Millilux mlx) | Low-Light Astronomical & Blackout Illumination Metric |
Step-by-Step Office Lighting Level & Inverse-Square Calculation Example
To calculate the illuminance level (E) delivered by a 4,000 Lumen LED ceiling luminaire (Φ = 4,000 lm) installed in an open-plan office desk area over a surface area of 8.0 square meters (A = 8.0 m2), and convert a required office desk rating of 500 Lux (500 lx) into Foot-Candles (fc) and Phots (ph):
Step 1 (Surface Illuminance Calculation): E = Φ ÷ A = 4,000 lm ÷ 8.0 m2 = 500 Lux (500 lm/m2)
Step 2 (Foot-Candle Conversion): E = 500 Lux ÷ 10.7639104 = 46.4515 Foot-Candles (46.45 fc)
Step 3 (Phot Conversion): E = 500 Lux ÷ 10,000 = 0.050 Phots (0.050 ph)
Thus, the 4,000-lumen luminaire provides 500 Lux (or 46.45 Foot-Candles) of workspace illumination, perfectly matching OSHA commercial office lighting standards.
Real-World Architectural & Ecological Illuminance Benchmarks
Below is a comparative reference chart showing illuminance levels (Ev) across natural daylight, moonlight, office environments, and surgical operating rooms:
| Illuminated Environment / Natural Light Condition | Illuminance in Lux (lx / lm/m2) | Foot-Candles & Phots (fc / ph) | Architectural & Ecological Photometry Context |
|---|---|---|---|
| Starlight Overcast Night Sky (No Moon) | 0.0001 – 0.001 lx | 0.0000093 – 0.000093 fc (0.1 – 1.0 nox) | Nocturnal ecosystem wildlife baseline lighting |
| Full Moon Clear Night Sky | 0.25 – 1.0 lx | 0.023 – 0.093 fc | Natural night moonlit ground illumination level |
| Residential Living Room / Building Corridor | 100.0 – 150.0 lx | 9.29 – 13.94 fc | Comfortable ambient home indoor illumination |
| Commercial Office Desk / Classroom Workspace | 500.0 lx (500 lm/m2) | 46.45 Foot-Candles (46.45 fc) | OSHA & CIBSE recommended office task lighting |
| Precision Surgical Operating Room / Micro-Assembly | 10,000.0 – 20,000.0 lx | 929.0 – 1,858.0 fc (1.0 – 2.0 phots) | High-intensity shadowless surgical task lighting |
| Full Daylight Overcast Sky (No Direct Sun) | 10,000.0 – 25,000.0 lx | 929.0 – 2,322.5 fc (1.0 – 2.5 phots) | Diffused outdoor daylight ambient light level |
| Direct Unshaded Summer Sunlight (Noon) | 100,000.0 – 130,000.0 lx | 9,290.3 – 12,077.4 fc (10.0 – 13.0 phots) | Peak solar ground surface illuminance level |
History & Physics: 1760 Inverse-Square Law vs 1948 CGPM Lux Standard
1760 Johann Lambert & The Inverse-Square Law of Illuminance (E = I ÷ r2)
In 1760, German polymath Johann Heinrich Lambert published Photometria, formulating the fundamental law of illuminance: incident light intensity (E) from a point light source decreases inversely with the square of distance (r) and proportionally with the cosine of the incident angle (θ): E = (I · &cos;θ) ÷ r2. This law forms the physical basis of all architectural lighting design.
1948 CGPM SI Standardization of the Lux (1 lx = 1 lm/m2)
In 1948, the 9th General Conference on Weights and Measures (CGPM) adopted the Lux (lx) as the official SI unit of illuminance (1 lux = 1 lumen per square meter). The SI lux replaced legacy regional units such as the CGS phot (1 phot = 10,000 lux) and British imperial foot-candle (1 fc = 10.7639 lux).
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Frequently Asked Questions (FAQ)
How do you convert Foot-Candles (fc) to Lux (lx)?
To convert Foot-Candles to SI Lux, multiply fc by 10.7639104 (or roughly 10.764). For example, 50 foot-candles × 10.764 = 538.2 Lux.
How do you convert Lux (lx) to Foot-Candles (fc)?
To convert Lux to Foot-Candles, divide Lux by 10.7639104 (or multiply by 0.092903). For example, 500 Lux ÷ 10.764 = 46.45 Foot-Candles.
What is the recommended Lux level for an office desk?
Under OSHA and CIBSE standards, recommended office desk task lighting is 500 Lux (approx. 46.5 Foot-Candles). Hallways and stairwells require 100 to 150 Lux.
What is the difference between Lux (Illuminance) and Lumens (Luminous Flux)?
Lumens (lm) measure the total total light output emitted by a lamp in all directions. Lux (lx = lm/m2) measures how much light actually lands on a surface area.