Watt to Lux Calculator

Q: How do you convert watts to lux?

To convert watts to lux, use the formula: lux = (watts × luminous efficacy) ÷ distance². First convert watts to lumens using efficacy, then divide by area (distance squared).

Q: Why do you need distance to convert watts to lux?

Lux measures illuminance per unit area. Light intensity decreases with distance due to the inverse square law, so you need the distance from the light source to calculate surface illumination.

Q: What factors affect watt to lux conversion?

The conversion depends on luminous efficacy (light source efficiency in lm/W) and distance from the source. LED efficiency ranges from 80-200+ lm/W, while incandescent bulbs only achieve 10-17 lm/W.

Convert watts to lux with step-by-step calculations. Perfect for lighting design, energy efficiency analysis, and illuminance calculations.

Power to Illuminance Converter

Watts (W):

Efficacy (lm/W):

Distance (m):

Light Type:

0.5m (Close) 1m (Standard) 2m (Medium) 3m (Far)

Common Watt to Lux Conversions

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Understanding Watt to Lux Conversion

Converting watts to lux requires two steps: first converting electrical power to luminous flux using luminous efficacy, then converting flux to illuminance using the inverse square law and distance.

Conversion Formula

lux = (watts × luminous efficacy) ÷ distance²

Step 1: lumens = watts × efficacy (lm/W)
Step 2: lux = lumens ÷ distance² (m²)

Where:
• lux = illuminance (light per unit area)
• watts = electrical power consumed
• efficacy = luminous efficacy (lm/W)
• distance = distance from source (meters)

Key Concepts

Watts (W): Electrical power consumed by the light source
Lux (lx): Illuminance - the amount of light falling on a surface per unit area
Luminous Efficacy: How efficiently electricity is converted to visible light (lm/W)
Inverse Square Law: Light intensity decreases with the square of distance

Illuminance Examples by Light Source

Light Source	Power	Efficacy	Lux at 1m	Lux at 2m
60W Incandescent	60W	12 lm/W	720 lx	180 lx
15W CFL	15W	60 lm/W	900 lx	225 lx
10W LED	10W	100 lm/W	1000 lx	250 lx
8W High-Eff LED	8W	150 lm/W	1200 lx	300 lx
50W Halogen	50W	20 lm/W	1000 lx	250 lx

Frequently Asked Questions

How do you convert watts to lux?

First convert watts to lumens using luminous efficacy, then divide by distance squared: lux = (watts × efficacy) ÷ distance². Both efficacy and distance are crucial for accurate conversion.

Why do you need distance to convert watts to lux?

Lux measures illuminance per unit area. Due to the inverse square law, light intensity decreases with distance, so you need the distance from the light source to calculate surface illumination.

What factors affect watt to lux conversion?

The conversion depends on luminous efficacy (varies by technology: LED 80-200+ lm/W, CFL 50-70 lm/W, incandescent 10-17 lm/W) and distance from the source (follows inverse square law).