# Illumination Converter

> Convert between illuminance (illumination) units: lux, foot-candle, phot, lumen per square meter, lumen per square foot, and more.

**Category:** Conversion
**Keywords:** illumination, illuminance, lux, foot-candle, phot, lumen, light, brightness, lighting
**URL:** https://complete.tools/illumination-converter

## How it calculates

The converter uses lux as the base unit and applies standardized conversion factors:

1 lux (lx) = 1 lumen/m² (SI base unit)
1 foot-candle (fc) = 10.76391 lux
1 phot (ph) = 10,000 lux
1 lumen/m² = 1 lux (by definition)
1 lumen/ft² = 10.76391 lux (equivalent to 1 foot-candle)
1 lumen/cm² = 10,000 lux (equivalent to 1 phot)
1 nox = 0.001 lux (millilux, used for astronomy and very low light)

The conversion formula is: result = value × (fromUnitFactor / toUnitFactor)

For example, to convert 500 lux to foot-candles: 500 × (1 / 10.76391) = 46.45 fc

The foot-candle value (10.76391) comes from the relationship between square meters and square feet: 1 m² = 10.76391 ft², since illuminance is flux per area.

## Who should use this

1. Lighting designers specifying illuminance levels for commercial and residential spaces, needing to convert between international (lux) and US (foot-candle) standards.
2. Photographers and cinematographers calculating exposure and determining proper lighting setups using light meters that may display in different units.
3. Architects and interior designers ensuring compliance with building codes that specify minimum light levels in various units.
4. Workplace safety officers verifying that office, industrial, and healthcare facilities meet OSHA or local illumination requirements.
5. Astronomers and researchers working with very low light measurements who need to convert between nox and lux.
6. Museum curators and archivists managing light exposure limits for sensitive artifacts and documents.

## Workplace lighting standards

Different work environments require specific illuminance levels for safety and productivity:

Office work: 300-500 lux (28-46 fc) for general tasks, 500-750 lux (46-70 fc) for detailed work
Industrial assembly: 300-750 lux (28-70 fc) depending on precision required
Warehouses and storage: 100-200 lux (9-19 fc)
Corridors and stairs: 100-150 lux (9-14 fc)
Operating rooms: 10,000-100,000 lux (930-9300 fc) at the surgical field
Retail spaces: 300-500 lux (28-46 fc) general, up to 1000 lux (93 fc) for displays

OSHA requires minimum 5 fc (54 lux) for general construction areas and 10 fc (108 lux) for first aid stations.

## Photography applications

Photographers use illuminance measurements to calculate exposure settings:

Bright sunlight: 100,000 lux (9,300 fc)
Overcast daylight: 1,000-10,000 lux (93-930 fc)
Indoor office lighting: 300-500 lux (28-46 fc)
Living room lighting: 50-150 lux (5-14 fc)
Candlelight: 10-15 lux (1-1.4 fc)
Full moon: 0.25 lux (0.023 fc)

The relationship between illuminance and exposure is: EV = log2(E × S / C), where E is illuminance in lux, S is ISO, and C is calibration constant.

## Worked examples

Example 1: An American lighting specification calls for 50 foot-candles in a workspace. What is this in lux?
50 fc × 10.76391 = 538.2 lux

Example 2: A museum limits artwork exposure to 50 lux. Convert to foot-candles for a US conservator.
50 lux ÷ 10.76391 = 4.65 foot-candles

Example 3: A scientific paper reports measurements in phot. Convert 0.5 phot to lux.
0.5 ph × 10,000 = 5,000 lux

Example 4: An astronomical observation reports 500 nox. What is this in lux?
500 nox × 0.001 = 0.5 lux

Example 5: Convert 1000 lumen/ft² to lumen/cm².
1000 lm/ft² = 10,763.91 lux = 1.076 lm/cm²

## Limitations

1. Illuminance only measures the quantity of light reaching a surface, not how it appears to the human eye (luminance) or color quality (CRI).
2. The tool assumes standard conversion factors and does not account for measurement uncertainties or instrument calibration differences.
3. Phot and nox are historical units rarely used in modern standards but included for legacy document conversions.
4. Real-world lighting varies significantly across surfaces; illuminance is typically measured at specific points and may not represent average conditions.
5. The tool does not convert to or from luminance units (candela/m², nits, foot-lambert) which measure light emitted or reflected from surfaces.

## FAQs

**Q:** What is the difference between illuminance and luminance?


**A:** Illuminance (measured in lux or foot-candles) is light falling ON a surface. Luminance (measured in candela/m² or nits) is light coming FROM a surface, either emitted or reflected.


**Q:** Why are foot-candles still used when lux is the SI standard?


**A:** Foot-candles remain common in the United States, particularly in building codes, IESNA standards, and industrial specifications. Most of the world uses lux exclusively.


**Q:** How do I measure illuminance?


**A:** Use a lux meter (light meter) with the sensor pointed toward the light source at the measurement surface. Many smartphone apps provide approximate readings using the camera sensor.


**Q:** What illuminance level is comfortable for reading?


**A:** 300-500 lux (28-46 fc) is recommended for reading printed material. Screens may require lower ambient light to reduce glare.


**Q:** How does distance affect illuminance?


**A:** Illuminance follows the inverse square law: doubling the distance from a point light source reduces illuminance to one-quarter. Moving from 1m to 2m from a lamp reduces light intensity by 75%.

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