Lighting Lux Calculator
Free Lighting lux Calculator for electrical engineering projects. Enter dimensions to get material lists and cost estimates.
Formula
Lux = (Total Lumens x UF x MF) / Area (m2)
The effective illuminance in lux equals the total luminous flux in lumens multiplied by the utilization factor and maintenance factor, divided by the area in square meters. The utilization factor accounts for how much light reaches the work plane, and the maintenance factor accounts for light loss over time from aging and dirt.
Worked Examples
Example 1: Office Illumination Check
Problem: An office is 100 sq meters with 12 fixtures producing 3,000 lumens each. UF is 0.55 and MF is 0.8. Calculate the lux level.
Solution: Total lumens: 12 x 3,000 = 36,000 lm\nEffective lux: (36,000 x 0.55 x 0.8) / 100 = 158.4 lux\nThis is below the 500 lux requirement for offices.\nLumens needed: (500 x 100) / (0.55 x 0.8) = 113,636 lm\nFixtures needed: 113,636 / 3,000 = 38 fixtures
Result: 158.4 lux (below 500 lux target) | Need 38 fixtures
Example 2: Warehouse Lighting
Problem: A 500 sq meter warehouse needs 200 lux. Each high-bay fixture produces 20,000 lumens. UF = 0.45, MF = 0.75.
Solution: Lumens needed: (200 x 500) / (0.45 x 0.75) = 296,296 lm\nFixtures needed: 296,296 / 20,000 = 15 fixtures\nActual lux: (15 x 20,000 x 0.45 x 0.75) / 500 = 202.5 lux
Result: Need 15 high-bay fixtures | Actual: 202.5 lux
Frequently Asked Questions
What is lux and how is it measured?
Lux is the SI unit of illuminance, measuring the amount of light that falls on a surface. One lux equals one lumen per square meter. A lux meter (light meter) placed on the work surface measures the illuminance at that point. Typical values range from 100 lux for corridors to 500 lux for offices and up to 1,000 lux for detailed work areas. Natural daylight provides about 10,000-25,000 lux outdoors and 500-1,000 lux near windows indoors. Understanding lux levels is essential for designing spaces that are comfortable, safe, and productive.
What is the difference between lumens and lux?
Lumens measure the total amount of visible light emitted by a source, while lux measures how much of that light actually lands on a surface. A 3,000-lumen fixture produces the same lumens regardless of room size, but the lux level depends on how that light is distributed. In a small 10 sq meter room, 3,000 lumens gives 300 lux, but in a 30 sq meter room the same fixture only provides 100 lux. Think of lumens as the total water flow from a sprinkler, and lux as how wet a specific spot on the ground gets.
What are the recommended lux levels for different spaces?
The Illuminating Engineering Society (IES) recommends the following minimum maintained lux levels: 50 lux for parking garages and outdoor walkways, 100 lux for corridors and stairways, 150-200 lux for lobbies and restrooms, 300 lux for general retail and conference rooms, 500 lux for offices and classrooms, 750 lux for detailed mechanical work, and 1,000 lux or more for surgical suites and precision manufacturing. These values represent the minimum maintained illuminance on the task surface, accounting for lamp depreciation and dirt accumulation over time.
How do I convert between lux and foot-candles?
Foot-candles (fc) are the imperial equivalent of lux, measuring 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 lux to foot-candles, divide by 10.764. To convert foot-candles to lux, multiply by 10.764. The IES in North America often specifies requirements in foot-candles while international standards use lux. For example, the common office recommendation of 50 foot-candles equals approximately 500 lux.
How do I interpret the result?
Results are displayed with a label and unit to help you understand the output. Many calculators include a short explanation or classification below the result (for example, a BMI category or risk level). Refer to the worked examples section on this page for real-world context.
What formula does Lighting Lux Calculator use?
The formula used is described in the Formula section on this page. It is based on widely accepted standards in the relevant field. If you need a specific reference or citation, the References section provides links to authoritative sources.