Illumination Conversion
Value:
Popular Illumination Converters:
What is a Illumination Converter?
An illumination converter is a tool that converts between units of illuminance such as lux, foot-candle, meter-candle, and phot. It is used in lighting design, architecture, photography, and workplace safety to ensure proper light levels.
History of Illumination Measurement
The lux (Latin for "light") is the SI unit of illuminance, equal to one lumen per square meter. The foot-candle, used in the US, was historically defined as illumination from a standard candle at one foot distance. The phot (10,000 lux) is a CGS unit from older scientific literature.
About This Illumination Converter
This illumination converter supports 11 units including lux, foot-candle, meter-candle, centimeter-candle, flame, nox, phot, lumen/m², lumen/cm², lumen/ft², and candela steradian/m². It covers SI, imperial, and CGS illuminance units.
Understanding Illumination (Illuminance)
Illuminance measures the amount of luminous flux (light) incident on a surface per unit area. It quantifies how brightly a surface is lit, as perceived by the human eye. The SI unit is the lux (lx), equal to one lumen per square meter. The foot-candle (fc) is the US customary equivalent, equal to one lumen per square foot. Other units include the phot (CGS, = 10,000 lux) and the nox (1 millilux, used for low-light measurements).
Illumination conversion is essential in architectural lighting design, photography, workplace safety regulations, and horticulture. US lighting standards specify illuminance in foot-candles (e.g., 50 fc for offices), while international standards use lux (500 lux for the same office). Converting between these ensures compliant designs regardless of which standard is referenced. Understanding these conversions also helps photographers match exposure settings across different light meter systems.
How to Convert Between Illuminance Units
Illuminance conversion is based on the relationship between the lumen and the area units:
- Identify the source and target illuminance units (lux, foot-candle, phot, nox).
- The key conversion: 1 foot-candle = 10.764 lux (since 1 ft² = 0.0929 m², and 1/0.0929 ≈ 10.764).
- For phot: 1 phot = 10,000 lux = 1 lumen/cm².
- For nox: 1 nox = 0.001 lux = 1 millilux.
- Verify direction: foot-candles to lux always gives a larger number (×10.764).
Key Illuminance Conversion Formulas
Essential relationships between illumination units:
- 1 foot-candle (fc) = 10.7639 lux
- 1 lux = 0.09290 fc
- 1 phot = 10,000 lux = 929.0 fc
- 1 lux = 10⁻⁴ phot
- 1 nox = 0.001 lux = 1 millilux
- 1 lux = 1 lm/m² (definition)
- 1 fc = 1 lm/ft² (definition)
Worked Examples — Illuminance Conversions
Example 1: US office standard specifies 50 foot-candles at desk level. What is this in lux?
Solution:
Conversion: 1 fc = 10.7639 lux.
Multiply: 50 × 10.7639 = 538.2 lux.
Answer: 50 fc = 538 lux ≈ 500 lux (the international standard for office lighting is 500 lux, closely matching).
Example 2: A greenhouse requires 25,000 lux for tomatoes. Express in foot-candles.
Solution:
Conversion: 1 lux = 0.09290 fc.
Multiply: 25,000 × 0.09290 = 2322.5 fc.
Answer: 25,000 lux = 2323 fc — intense supplemental lighting needed in winter.
Example 3: A scientific instrument measures starlight at 0.002 lux. Express in nox.
Solution:
Conversion: 1 nox = 0.001 lux, so 1 lux = 1000 nox.
Multiply: 0.002 × 1000 = 2 nox.
Answer: 0.002 lux = 2 nox — the nox unit is convenient for astronomical twilight levels.
Example 4: An old optics textbook specifies 0.5 phot illumination. Convert to lux and foot-candles.
Solution:
To lux: 0.5 × 10,000 = 5000 lux.
To fc: 5000 × 0.09290 = 464.5 fc.
Answer: 0.5 phot = 5000 lux = 465 fc — very bright, like outdoor shade on a sunny day.
Illuminance Conversion Quick Reference
Common illumination conversions with typical real-world values:
| From | To |
|---|---|
| 1 fc | 10.764 lux |
| 1 lux | 0.0929 fc |
| 1 phot | 10,000 lux |
| 1 nox | 0.001 lux |
| 100 fc | 1076 lux |
| 500 lux | 46.5 fc |
| 10,000 lux | 929 fc |
| 100,000 lux | 9290 fc |
| 1 lux | 1000 nox |
| 0.25 lux | 250 nox |
| 50 fc | 538 lux |
| 30 fc | 323 lux |
Understanding Illumination Measurement Systems
The SI unit lux (lx) is defined as one lumen per square meter. It is based on the candela (SI base unit for luminous intensity) weighted by the human eye's spectral sensitivity (photopic response). The lux measures how bright a surface appears to a human observer — it is a photometric quantity, not a radiometric one. The international lighting standard (ISO 8995) specifies workplace illuminance in lux: 500 lux for offices, 750 lux for technical drawing, 200 lux for corridors.
The foot-candle (fc = 1 lumen per square foot) is standard in US lighting practice (IES standards). Since 1 ft² = 0.0929 m², a uniform flux creates 10.764× more lux than foot-candles over the same area — hence the conversion factor. The phot (= 10,000 lux = 1 lm/cm²) is the CGS unit, rarely used today but found in older optics literature. The nox (= 0.001 lux) was proposed for scotopic (night vision) measurements and appears in research on nocturnal ecology and astronomical twilight quantification.
Real-World Applications of Illuminance Conversion
Architectural Lighting Design
Designers working with international clients must convert between IES foot-candle standards (US) and ISO lux standards (international). A 30 fc corridor standard = 323 lux, which must match EN 12464 specifications for European projects.
Photography & Cinematography
Light meters may read in lux or fc depending on origin. Exposure calculations require consistent units. Converting ensures proper exposure: EV 0 = 2.5 lux, and each EV step doubles the illuminance.
Workplace Safety
OSHA (US) specifies minimum lighting in fc; international standards use lux. Converting ensures compliance regardless of which regulation applies. Emergency lighting minimums: 10.8 lux (1 fc) at floor level.
Horticulture
Plant light requirements specified in lux (or more precisely PPFD in µmol/m²/s for PAR). Converting between fc and lux helps greenhouse operators interpret older growing guides written in US customary units.
Museum & Gallery Conservation
Light-sensitive artworks have maximum exposure limits: 50 lux for textiles and watercolors, 200 lux for oil paintings. Converting from fc-rated track lights ensures artwork protection in US and international venues.
Common Pitfalls in Illumination Conversion
The most common confusion is between illuminance (lux, light hitting a surface) and luminance (cd/m², light emitted or reflected from a surface). A white wall illuminated at 500 lux has luminance of about 160 cd/m² (assuming 80% reflectance and Lambertian reflection), while a black surface at the same illuminance might have only 25 cd/m². Another frequent error is assuming lux indicates the "brightness" of a light source — it does not. Lux depends on distance: a 100W bulb produces different lux at different distances (inverse square law). The source strength is measured in lumens (total flux) or candela (intensity per solid angle). Finally, beware of the spectral weighting: lux is photopically weighted for human daytime vision. For plants, PPFD (µmol/m²/s) is more relevant, and the conversion from lux to PPFD depends on the light spectrum — there is no single conversion factor.
Key Takeaways
- 1 foot-candle = 10.764 lux — the fundamental conversion between US and international illuminance.
- Lux = lumens per m²; foot-candle = lumens per ft². The difference is purely the area unit.
- Typical values: direct sunlight ≈ 100,000 lux; office ≈ 500 lux; full moon ≈ 0.25 lux.
- The phot (10,000 lux) is obsolete; the nox (0.001 lux) is used only in specialized night research.
- Illuminance (lux) measures light ON a surface; luminance (cd/m²) measures light FROM a surface.
- Human eyes adapt over ~6 orders of magnitude: 0.001 lux (starlight) to 100,000 lux (sunlight).
Metric Conversion Factor Tables for Illumination Converter
| Units to convert | Multiply By The Number | Convert as Unit |
|---|---|---|
| Lux (lx) | 1 | Meter-candle (m*c) |
| Lux (lx) | 0.0001 | Centimeter-candle (cm*c) |
| Centimeter-candle (cm*c) | 10000 | Lux (lx) |
| Lux (lx) | 1 | Lumen/square meter (lm/m²) |
| Lux (lx) | 0.09290304 | Lumen/square foot (lm/ft²) |
| Lumen/square foot (lm/ft²) | 10.763910417 | Lux (lx) |
| Meter-candle (m*c) | 0.09290304 | Foot-candle (ft*c) |
| Foot-candle (ft*c) | 10.763910417 | Meter-candle (m*c) |
| Phot (ph) | 10000000 | Nox |
| Nox | 1e-7 | Phot (ph) |
Illuminationconverters & it's abbreviations
| Unit | Abbreviation | Unit | Abbreviation | Unit | Abbreviation |
|---|---|---|---|---|---|
| lux | lx | meter-candle | m*c | centimeter-candle | cm*c |
| foot-candle | ft*c, fc | flame | - | nox | - |
| candela steradian/sq. meter | - | lumen/square meter | lm/m² | lumen/square centimeter | lm/cm² |
| lumen/square foot | lm/ft² |
Frequently Asked Questions
How do I convert lux to foot-candles?
Divide the lux value by 10.764 to get foot-candles. For example, 500 lux ÷ 10.764 = 46.5 foot-candles.
How do I convert foot-candles to lux?
Multiply the foot-candle value by 10.764 to get lux. For example, 50 fc × 10.764 = 538.2 lux.
What is the recommended lux level for an office?
Typical office lighting should be 300-500 lux (28-46 foot-candles). Detailed work like drafting may require 500-1000 lux. Corridors need only 100-150 lux.
What is the difference between lux and lumen?
Lumens measure total light output from a source. Lux measures how much light reaches a surface (lumens per square meter). A 1000-lumen bulb produces different lux levels depending on distance and room size.
Is lux the same as lumen per square meter?
Yes, 1 lux equals exactly 1 lumen per square meter. Lux is simply the special name given to this derived SI unit of illuminance.
Complete list of Illumination conversion units and its conversion.
- 1 lux = 1 meter-candle
lux to meter candle → - 1 meter-candle = 1 lux
meter candle to lux → - 1 lux = 0.0001 centimeter-candle
lux to cm candle →
- 1 lux = 0.09290304 lumen/square foot
lux to lumen per sq ft → - 1 lumen/square foot = 10.763910417 lux
lumen per sq ft to lux → - 1 meter-candle = 0.0001 centimeter-candle
meter candle to cm candle →
- 1 phot = 10000000 nox
phot to nox → - 1 nox = 1.E-7 phot
nox to phot → - 1 candela steradian/sq. meter = 0.0001 lumen/square centimeter
lumen per sq m to lumen per sq cm →
- 1 centimeter-candle = 10000 lux
cm candle to lux → - 1 lux = 1 lumen/square meter
lux to lumen per sq m → - 1 lumen/square meter = 1 lux
lumen per sq m to lux →
- 1 centimeter-candle = 10000 meter-candle
cm candle to meter candle → - 1 meter-candle = 0.09290304 foot-candle
meter candle to ft candle → - 1 foot-candle = 10.763910417 meter-candle
ft candle to meter candle →
- 1 lumen/square centimeter = 10000 candela steradian/sq. meter
lumen per sq cm to lumen per sq m →