Watts to Lumens Converter Formula

Understand the math behind the watts to lumens converter. Each variable explained with a worked example.

Use the Watts to Lumens Converter

Formulas Used

Estimated Lumens

lumens = watts * efficacy

Incandescent Equivalent

incandescent_equiv = watts * efficacy / 14

Variables

VariableDescriptionDefault
wattsBulb Wattage(W)10
efficacyBulb Type (Efficacy)(lm/W)90

How It Works

Watts to Lumens

Lumens = Watts x Luminous Efficacy (lm/W)

Typical Efficacy by Bulb Type

Bulb TypeEfficacy (lm/W) Incandescent12-17 Halogen16-24 CFL50-70 LED80-120 High-efficiency LED100-150

A 10W LED produces roughly the same light as a 60W incandescent bulb.

Worked Example

10 watt LED bulb.

watts = 10efficacy = 90
  1. 01Lumens = 10W x 90 lm/W = 900 lumens
  2. 02Incandescent equivalent = 900 / 14 = 64W

Frequently Asked Questions

Why compare watts to lumens?

Watts measure energy consumed, lumens measure light produced. With different bulb technologies, the same wattage produces vastly different amounts of light. Lumens are the true measure of brightness.

How many lumens do I need?

For reference: 450 lm = 40W incandescent equivalent, 800 lm = 60W, 1100 lm = 75W, 1600 lm = 100W. Most rooms need 1,500-3,000 total lumens.

Ready to run the numbers?

Open Watts to Lumens Converter