Watts to Lux Calculator
Convert electrical power to illuminance for lighting design and photometry calculations
Photometry Calculator
Watts → Lux
Calculate illuminance from electrical power
Lux → Watts
Calculate required power from target illuminance
80-120 lm/W
Light output per unit of electrical power input
Electrical power consumed by the light source
Area of the illuminated surface
Photometry Results
Formula: Enter values to see calculation
Light Source: LED Bulb (90 lm/W)
Example Calculations
Example 1: LED Room Lighting
Setup: 10W LED bulb (100 lm/W) in 20m² room
Calculation: E = (10W × 100lm/W) / 20m² = 50 lux
Result: Provides moderate ambient lighting suitable for living areas
Example 2: Office Workspace
Target: 500 lux for 10m² desk area using fluorescent tubes (72 lm/W)
Calculation: P = (500lx × 10m²) / 72lm/W = 69.4W
Result: Need approximately 70W of fluorescent lighting
Example 3: Energy-Efficient Comparison
Comparison: 60W incandescent (15 lm/W) vs 10W LED (100 lm/W)
Incandescent: 900 lumens total output
LED: 1000 lumens total output (11% more light, 83% less power)
Illuminance Standards
Light Source Efficacy
Unit Conversions
Understanding Photometry: Watts, Lumens, and Lux
Key Photometric Units
- •Watts (W): Electrical power consumed by the light source
- •Lumens (lm): Total light output from a source (luminous flux)
- •Lux (lx): Light intensity per unit area (illuminance)
- •Efficacy (lm/W): Light output efficiency of a source
The Relationship
Step 1: Watts × Efficacy = Lumens (total light output)
Step 2: Lumens ÷ Area = Lux (light per unit area)
Practical Applications
Lighting Design
- • Calculate required wattage for target illuminance
- • Compare efficiency of different light sources
- • Plan lighting layouts for optimal coverage
- • Meet building code lighting requirements
Energy Management
- • Calculate energy costs and savings
- • Optimize lighting for energy efficiency
- • Compare LED vs traditional lighting
- • Plan sustainable lighting systems
Why Conversion Matters
Energy Efficiency
Different light sources have vastly different efficacies. LEDs can produce 6x more light per watt than incandescent bulbs, dramatically reducing energy costs while maintaining the same illuminance levels.
Proper Illumination
Understanding the watts-to-lux relationship helps ensure adequate lighting for specific tasks while avoiding over-illumination that wastes energy and can cause discomfort.