Illuminance Converter Calculator
Convert between all common illuminance units. From lux for international lighting standards to foot-candles for US building codes, this converter helps lighting designers, photographers, and safety professionals work across measurement systems.
Understanding Illuminance Measurement
Illuminance measures the amount of light falling on a surface per unit area. The SI unit is the lux, defined as one lumen per square meter. A lumen measures the total perceived light output from a source, while lux accounts for how that light spreads across a surface. The same lamp produces lower lux at greater distances because its light covers more area.
The foot-candle is the US customary unit, defined as one lumen per square foot. Since one square meter equals about 10.764 square feet, one foot-candle equals approximately 10.764 lux. US building codes, OSHA regulations, and IESNA lighting recommendations frequently use foot-candles, while international standards use lux.
Lighting professionals measure illuminance with a lux meter or light meter. These instruments use a photodiode calibrated to match human eye sensitivity across the visible spectrum. Readings should be taken at the work surface height, not at the light fixture, since illuminance decreases with the square of the distance from the light source.
Illuminance Standards for Different Spaces
Workplace lighting standards exist to protect worker health and productivity. Office spaces require 300-500 lux per European EN 12464-1 standards, which translates to about 28-46 foot-candles. Detailed assembly work may need 750-1,000 lux. Hospital operating rooms require 10,000-100,000 lux at the surgical field.
Retail environments use lighting strategically. General sales floor lighting runs 300-500 lux, but accent lighting on featured merchandise can reach 1,500-3,000 lux to draw attention. Grocery stores aim for 500-750 lux to make produce look fresh and appealing. Restaurant ambiance varies from 50 lux for romantic dining to 300 lux for casual fast-service establishments.
Outdoor lighting standards address safety and light pollution. Street lighting ranges from 5 lux for residential side streets to 30 lux for major highways. Parking lots need 10-50 lux depending on activity level. Sports venues require 500-2,000 lux for professional play with TV cameras. Many jurisdictions now regulate maximum outdoor illuminance to reduce light pollution affecting astronomy and wildlife.
Illuminance in Photography and Cinematography
Photographers use illuminance to plan exposure settings. The sunny 16 rule states that on a bright sunny day (about 100,000 lux), correct exposure at ISO 100 uses f/16 and 1/100 second shutter speed. On an overcast day at 10,000 lux, you open up to f/8. Converting between lux and foot-candles helps when working with lighting guides from different countries.
Studio lighting is measured in lux or foot-candles to ensure consistent exposure across the set. Portrait photography typically uses 500-2,000 lux. Product photography may use 2,000-5,000 lux. Cinematographers working on film sets need precise light level control, often measuring with dedicated cine meters that display in foot-candles or lux.
Security camera specifications list minimum illuminance requirements for acceptable image quality. A standard security camera might need 1-3 lux for color images, while infrared-capable cameras can work at 0 lux using their own IR illumination. Understanding these specifications in consistent units helps when designing surveillance systems that must perform reliably under varying lighting conditions throughout the day and night cycle.
Frequently Asked Questions
How do I convert lux to foot-candles?
Divide lux by 10.764 to get foot-candles, or multiply foot-candles by 10.764 to get lux. A well-lit office at 500 lux equals about 46.5 foot-candles. One foot-candle is the illumination on a surface one foot away from a standard candle.
What is the difference between lumens and lux?
Lumens measure total light output from a source. Lux measures light arriving on a surface (lumens per square meter). A 1,000-lumen bulb produces the same total light regardless of room size, but it creates more lux in a small room than a large one because the light is concentrated over less area.
How much lux do I need for an office?
Standard recommendations are 300-500 lux for general office work, 500-750 lux for detailed tasks like drafting, and 50-100 lux for corridors. These values come from lighting standards like EN 12464-1 in Europe and IESNA guidelines in North America.
What is a phot?
A phot is a CGS unit of illuminance equal to 10,000 lux or about 929 foot-candles. It is rarely used in modern practice but appears in older scientific literature. Direct sunlight provides roughly 10 phots or 100,000 lux.
How does natural daylight compare to artificial lighting?
Direct sunlight provides about 100,000 lux. An overcast day gives 1,000-2,000 lux. A typical office has 300-500 lux. A living room in the evening might have 50-150 lux. Moonlight provides only about 0.25 lux. This enormous range shows why our eyes adapted to be logarithmic in their brightness perception.