Footcandle to Lux Converter — Free Online Calculator
Convert between footcandles and lux. Includes recommended lighting levels by space type.
How to Use This Calculator
Enter a value and select the conversion direction.
The Formula Explained
1 footcandle = 10.764 lux. Footcandles are used in the US, lux is the international standard.
Illuminance: The Light That Actually Reaches Surfaces
Light measurement distinguishes between the total light a source emits (lumens) and the light that actually reaches a surface (illuminance, measured in footcandles or lux). A 1,000-lumen bulb hanging in a large warehouse produces very different illuminance at the floor than the same bulb in a small bathroom because the light spreads over different areas. Illuminance is what matters for task performance, safety, and comfort — not the bulb rating itself.
The math: illuminance in lux = lumens / area in square meters. A 1,000 lumen source illuminating a 10 sq meter area produces 100 lux average. The same source in a 1 sq meter area produces 1,000 lux. Real-world calculations add fixture efficiency, light distribution pattern, reflection from walls and ceiling, and spacing effects. This is why professional lighting design uses software like AGi32 or Dialux to model illumination rather than simple formulas.
Worked Example: Office Lighting Design
A 500 sq ft (46.5 sq m) office with general office work tasks requiring 40 footcandles (about 430 lux) average illuminance. Ceiling height 9 ft, light-colored walls and ceiling (70% reflectance), desk height 30 inches.
Required lumens at work surface: 430 lux × 46.5 sq m = 20,000 lumens delivered to the work plane. Accounting for ceiling mounting height, light distribution, and room reflectance, the lumen output needed at the fixtures is about 25,000-30,000 lumens (coefficient of utilization typically 0.7-0.8 for this type of space).
Using 3,000 lumen 2x4 LED troffers (40W each): 30,000 / 3,000 = 10 fixtures. Layout: 2 rows of 5, spacing about 8 feet on centers. Total power: 400W. Light-to-watt: 75 lumens per watt.
Modern design targets 60-80 lumens per watt for commercial interior lighting. Energy codes (ASHRAE 90.1, California Title 24) limit lighting power density (LPD) to 0.6-0.8 W/sq ft for offices, so the 400W / 500 sq ft = 0.8 W/sq ft just meets code.
Worked Example: Parking Lot Lighting
A 200 ft × 150 ft parking lot (30,000 sq ft = 2,787 sq m) needs average 2 fc (21.5 lx) per IES parking lot recommendations for low-activity security.
Required average lumens delivered: 21.5 × 2,787 = 60,000 lumens at the pavement. Accounting for fixture utilization (about 0.5 for pole-mounted downlighting with wide dispersion) and light loss factors (0.7 for dirt, lumen depreciation, etc.), the fixture lumen output needed is about 170,000-200,000 lumens total.
Using 15,000 lumen LED shoebox fixtures (150W each) on 25 ft poles: 200,000 / 15,000 = 13 fixtures. Layout: 4 poles on short sides, spaced to avoid dark zones. Total power: 2,000W. Run 12 hours/night × 365 days = 4,380 hours/year. Annual energy: 2,000 × 4,380 / 1000 = 8,760 kWh. Cost at 10 cents commercial rate: 876 USD per year.
Replacing with previous HPS (400W each, 28,000 lumens) fixtures: would need 8 fixtures at 3,200W total, using 14,016 kWh per year at 1,402 USD. LED saves about 526 USD per year with better uniformity and 5x longer fixture life.
Footcandle/Lux Mistakes
1. Confusing lumens and lux. Lumens is source output, lux is surface illumination. A 1,000-lumen bulb does not produce 1,000 lux — it depends on distance and area.
2. Averaging over the whole room vs task area. IES recommendations apply to task areas, not overall room averages. A room with 40 fc average might have 10 fc at the desk if the light is concentrated elsewhere.
3. Ignoring light loss factor. Over 5-10 years, fixtures accumulate dust, lamps degrade, and wall reflectance decreases. Initial design should provide 20-30% more light than the final target to account for depreciation.
4. Using footcandles and lux interchangeably without conversion. 10x difference between the units. Always check what unit the specification uses.
5. Underlighting exits and egress paths. Fire and safety codes require minimum 1 fc at exits in occupied buildings during emergency mode. Normal operation levels must meet this plus margin.
Recommended Light Levels (IES RP-Series)
Residential:
Hallways, stairs: 5-10 fc (50-100 lx).
General rooms: 10-20 fc (100-200 lx).
Kitchen counters: 50-75 fc (500-750 lx).
Reading: 30-50 fc (300-500 lx).
Bathroom vanity: 30-50 fc (300-500 lx).
Commercial:
Office general: 30-50 fc (300-500 lx).
Retail general: 50-100 fc (500-1,000 lx).
Retail display: 100-500 fc (1,000-5,000 lx).
Warehouse general: 10-20 fc (100-200 lx).
Warehouse task: 30-50 fc (300-500 lx).
Parking lot: 1-5 fc (10-50 lx).
Industrial and specialized:
Machine shop general: 50-100 fc (500-1,000 lx).
Precision assembly: 100-200 fc (1,000-2,000 lx).
Inspection work: 200-500 fc (2,000-5,000 lx).
Hospital operating room: 1,000-2,500 fc (10,000-25,000 lx).
Standards and References
IES Lighting Handbook is the definitive reference for illuminance recommendations in North America. Specific recommended levels are published in RP (Recommended Practice) documents for different application types (offices, retail, sports, healthcare, education). CIE (International Commission on Illumination) publishes international equivalents. ASHRAE 90.1 and California Title 24 set energy code limits on lighting power density (watts per square foot) that interact with the illuminance targets.
Footcandle to lux: the two-system illumination conversion
Footcandles and lux both measure illuminance: lumens per area. Footcandles is US customary (lumens per sq-ft). Lux is metric (lumens per sq-meter). Since 1 sq-meter = 10.76 sq-ft, 1 fc = 10.76 lux. Most US lighting specs are in footcandles; international and modern LED datasheets use lux.
The formula and what it does
The conversion factor 10.764 is the area conversion (1 sq-m = 10.764 sq-ft). Light incident on a surface in lumens per sq-ft (fc) equals 10.764 times the same in lumens per sq-m (lux).
Worked example
Scenario: Office lighting spec calls for 500 lux at the work surface. Convert to footcandles.
fc = 500 / 10.764 = 46.5 fc. Roughly 50 fc, which matches IES recommendation for office task lighting. The unit choice does not change the design, just the number.
Common mistakes to avoid
undefinedFrequently asked questions
Why two different units for the same thing?
Historical. Lux is SI metric, footcandles is US customary. Most countries use lux. US is partially holdout, particularly in older specifications and codes.
What is a typical lux value for daylight?
Direct sunlight: 50,000-100,000 lux. Overcast day: 1,000-10,000 lux. Sunrise/sunset: 400 lux. Office: 300-500 lux. Living room: 50-100 lux. Twilight: 10 lux. Moonlight: 0.1-0.3 lux.
What about candela?
Different unit. Candela is luminous intensity (lumens per steradian), describing the directional output of a source. Lux/footcandle is the result of that intensity falling on a surface at some distance.
How do I measure footcandles?
Light meter held parallel to the work surface. Smartphone lux apps work okay (within 10-20 percent) for casual use. Cheap dedicated meters (Mastech, UNI-T) are accurate within 5 percent.
Does fc/lux change with light color?
No. Both measure photometric light (weighted to human eye response), so different LED color temps produce the same illuminance per lumen. Color affects perceived brightness slightly but not the meter reading.
Convert 1000 lumens output to footcandles at 10 ft?
For a point source: fc = lumens / (4 pi x distance squared) = 1000 / (12.57 x 100) = 0.8 fc. Real fixtures with reflectors deliver more than the inverse-square law suggests because they concentrate output.