Illuminance & Lux to Foot-Candles Calculator

Photometry, Architectural Lighting & Illuminance Metrology

Illuminance is the total luminous flux incident per unit surface area:

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• Universal Illuminance Conversion Formulas (IESNA & CIE Standards)**:

1 Foot-Candle (fc) = 1 lm/ft^2 = 10.76391 Lux (lx) = 10.76391 lm/m^2

E_fc = E_Lux10.76391 = E_Lux × 0.092903

1 Phot (ph) = 1 lm/cm^2 = 10,000 Lux = 929.03 fc

1 Nox (nx) = 0.001 Lux

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• Zonal Cavity Lumen Method for Lighting Layout**:

Φ_incident = E_Lux × A (Total Lumens Incident on Workplane)

N_fixtures = E_Lux × AUF × MF × Φ_lamp

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• Standard IESNA & EN 12464-1 Illuminance Recommendations**:

• Clear Full Moon: 0.25 Lux 0.0232 fc 250 Nox

• Living Room Ambient: 150.0 Lux 13.94 fc

• Commercial Office Desk: 500.0 Lux 46.45 Foot-Candles (Code required)

• Precision Inspection / Drafting: 1,000.0 Lux 92.90 fc

• Hospital Operating Room Surgery: 10,000.0 Lux 929.03 fc

• Direct Midday Sunlight: 100,000.0 Lux 9,290.3 fc 10.0 Phot

How to Use This Calculator

Enter your Illuminance Magnitude (E) (e.g. 500 in illuminance), From Illuminance Unit — choose from Lux (lx = lm/m² - SI Base Standard), Foot-Candles (fc = lm/ft² - US IESNA Standard), Phot (ph = lm/cm² = 10,000 Lux - CGS Unit), To Illuminance Unit — choose from Foot-Candles (fc = lm/ft²), Lux (lx = lm/m²), Phot (ph), Room Floor / Task Surface Area (A in m²) (e.g. 30 in m²), Single Luminaire Output (Lumens/fixture) (e.g. 3000 in lm), and IESNA & EN 12464-1 Lighting Benchmark — choose from Custom Illuminance Level, Commercial Office Desk (500.0 Lux) → 46.45 Foot-Candles | 15,000 total lumens (30m² room) | 11 LED fixtures, Direct Clear Midday Sunlight (100,000 Lux) → 9,290.3 fc | 10.0 Phot | Maximum natural daylight. Results update instantly as you type — adjust any value to compare scenarios.

The Formula

Multipliers to SI Base Unit Lux (lx = lm/m^2) (IESNA & EN 12464-1 Standards)

Standard commercial assumptions: Utilization Factor (UF) = 0.60, Maintenance Factor (MF) = 0.80 -> 0.48

Worked Example

An electrical lighting designer specifying illumination for a 30 m² office room targets 500 Lux (46.45 Foot-Candles) and calculates they need 11 LED fixtures of 3,000 lumens each to deliver code-compliant light.

Understanding Your Result

Unit conversions are exact by definition within a given measurement system (e.g., 1 km = exactly 1,000 m). Cross-system conversions (metric to imperial) use defined exchange factors: 1 inch = exactly 2.54 cm; 1 pound = 0.45359237 kg. Round your converted result to match the precision of your original measurement — expressing more decimal places than your input justifies implies false accuracy. For regulatory, legal, or safety-critical applications, verify which measurement system is required by the applicable standard.