Lux to Lumens Calculator
Convert between lux (illuminance) and lumens (luminous flux) based on area. Enter values for instant results with step-by-step formulas.
Formula
Lumens = Lux * Area (m2), Lux = Lumens / Area (m2)
Lux measures illuminance (light per unit area) in lumens per square meter. To convert lux to total lumens, multiply by the area in square meters. To convert lumens to lux, divide by the area. One foot-candle equals 10.764 lux.
Worked Examples
Example 1: Office Lighting Design
Problem: An office space is 10 square meters and requires 500 lux for desk work. How many lumens are needed and how many 800-lumen LED bulbs are required?
Solution: Total lumens = Lux * Area = 500 * 10 = 5,000 lumens\nWith 0.8 maintenance factor: 5,000 / 0.8 = 6,250 lumens needed\nNumber of 800-lumen LEDs = ceil(6,250 / 800) = 8 bulbs\nEstimated power = 6,250 / 100 lm/W = 62.5W\nFoot-candles = 500 * 0.0929 = 46.45 fc
Result: 5,000 lumens needed | 8 LED bulbs (800 lm each) | 62.5W total power
Example 2: Warehouse Illuminance from Existing Fixtures
Problem: A 200 square meter warehouse has 20 high-bay LED fixtures, each producing 15,000 lumens. What is the average lux level at floor level?
Solution: Total lumens = 20 * 15,000 = 300,000 lumens\nAverage lux = Total lumens / Area = 300,000 / 200 = 1,500 lux (theoretical)\nWith CU of 0.6 and LLF of 0.75: 1,500 * 0.6 * 0.75 = 675 lux\nFoot-candles = 675 * 0.0929 = 62.7 fc\nThis exceeds the 200-lux minimum for general warehouse lighting
Result: Effective illuminance: ~675 lux (62.7 fc) | Exceeds 200 lux warehouse minimum
Frequently Asked Questions
What is the difference between lux and lumens?
Lumens measure the total amount of visible light emitted by a source (luminous flux), while lux measures the amount of light falling on a surface per unit area (illuminance). One lux equals one lumen per square meter. A light bulb rated at 800 lumens always outputs 800 lumens regardless of the room size. However, the lux level on surfaces depends on how that light is distributed. In a small 5-square-meter room, 800 lumens produces 160 lux. In a 20-square-meter room, the same bulb produces only 40 lux. This distinction is crucial for lighting design because you need to achieve specific lux levels at the work surface for visual comfort and task performance, and the number of lumens needed depends on the room dimensions.
What are recommended lux levels for different spaces?
Lighting standards provide recommended illuminance levels based on task requirements and visual comfort. The Illuminating Engineering Society (IES) recommends: offices and classrooms need 300 to 500 lux for general work and 500 to 750 lux for detailed tasks. Retail spaces require 300 to 750 lux depending on merchandise type. Warehouses and storage areas need 100 to 200 lux for general areas and 300 lux at picking stations. Hospitals require 300 to 500 lux in examination rooms and 100 lux in corridors. Residential living rooms typically use 150 to 300 lux, kitchens 300 to 500 lux, and bedrooms 100 to 200 lux. Outdoor parking lots need 10 to 50 lux, while sports fields require 200 to 750 lux depending on competition level.
How do I convert between lux and foot-candles?
Foot-candles (fc) are the imperial equivalent of lux, measuring illuminance in lumens per square foot. The conversion is straightforward: 1 foot-candle equals 10.764 lux, or equivalently, 1 lux equals 0.0929 foot-candles. To convert from lux to foot-candles, multiply by 0.0929. To convert from foot-candles to lux, multiply by 10.764. Foot-candles are still commonly used in North America, particularly in building codes and IESNA standards, while lux is used internationally per the SI system. For quick mental conversion, dividing lux by 10 gives an approximate foot-candle value. For example, 500 lux is approximately 50 foot-candles (exact value: 46.45 fc). Many professional light meters display both units simultaneously.
What is luminous efficacy and how does it relate to lumens?
Luminous efficacy measures how efficiently a light source converts electrical power into visible light, expressed in lumens per watt (lm/W). Higher efficacy means more light output for less energy consumption. Modern LED bulbs achieve 80 to 150 lumens per watt, compared to compact fluorescent at 50 to 80 lm/W, halogen at 15 to 25 lm/W, and incandescent at 10 to 17 lm/W. This is why a 10W LED produces the same 800 lumens as a 60W incandescent bulb. When planning lighting installations, luminous efficacy determines the electrical load and energy cost. A room requiring 10,000 lumens needs only 100W of LED power versus 625W of incandescent power. Over a year of 8-hour daily use, this difference amounts to approximately 1,533 kWh of energy savings.
How do I measure lux levels in a room?
Lux levels are measured using a lux meter (also called an illuminance meter or light meter), which contains a photodiode sensor calibrated to match human eye sensitivity. Professional meters from manufacturers like Sekonic, Konica Minolta, or Extech cost $50 to $500 depending on accuracy. Smartphone apps can provide rough estimates but are typically 20 to 40 percent inaccurate because phone sensors are not properly calibrated. When measuring, place the sensor on the work surface (desk height, 30 inches for offices) facing upward to measure horizontal illuminance. Take multiple readings at different points since lighting is rarely uniform. Measure with the room set up normally including furniture, which can block and absorb light. Compare readings to IES recommended levels for the specific task performed at each location.
How do I get the most accurate result?
Enter values as precisely as possible using the correct units for each field. Check that you have selected the right unit (e.g. kilograms vs pounds, meters vs feet) before calculating. Rounding inputs early can reduce output precision.