Lumen to Watt & Luminous Efficacy Calculator (LED, CFL, Incandescent

Lumens, Watts, Luminous Efficacy & Energy Economics Metrology

Watts measure electrical energy consumed per second, whereas Lumens measure the total rate of visible light emitted weighted by the photopic eye response V(λ):

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• Universal Lumen to Watt Conversion Formula**:

P_Watts = Φ_Lumensη_Efficacy

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• Luminous Efficacy of Common Light Sources**:

• Standard Incandescent Bulb: 12 to 15 lm/W 90% wasted as heat

• Halogen Lamp: 18 to 22 lm/W Slightly higher tungsten filament temp

• CFL (Compact Fluorescent): 50 to 70 lm/W Gas discharge phosphor

• T8 Linear Fluorescent: 75 to 90 lm/W Commercial ceiling fixtures

• Standard Modern LED Bulb: 90 to 120 lm/W Standard consumer A19

• Commercial High-Efficiency LED: 130 to 180 lm/W High bays & streetlights

• Theoretical Physics Maximum: 683 lm/W Monochromatic green at λ = 555 nm

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• Standard Incandescent Wattage vs LED Lumens**:

• 40W Incandescent: ≈ 450 Lumens 4.5W to 5.5W LED

• 60W Incandescent: ≈ 800 Lumens 7.5W to 9.0W LED

• 75W Incandescent: ≈ 1,100 Lumens 10.0W to 12.0W LED

• 100W Incandescent: ≈ 1,600 Lumens 14.0W to 17.0W LED

• 150W Incandescent: ≈ 2,600 Lumens 22.0W to 26.0W LED

How to Use This Calculator

Enter your Luminous Flux (Lumens / lm) (e.g. 800 in lm), Lighting Technology & Luminous Efficacy — choose from LED High-Efficiency (100 lm/W - Modern LED Bulb), LED Commercial High-Efficacy (150 lm/W - Industrial Fixture), CFL Compact Fluorescent (60 lm/W - Spiral CFL), Daily Operating Usage (Hours/day) (e.g. 5.0 in hrs/day), Electricity Tariff Rate (/kWh) (e.g. 0.16 in /kWh), and Bulb Replacement & Lighting Benchmark — choose from Custom Flux & Efficacy, Night Light / Accent (100 lm) → 1.0W LED vs 7.5W Incandescent, 60W Incandescent Equivalent (800 lm) → 8.0W LED (86.7% Energy Saved). Results update instantly as you type — adjust any value to compare scenarios.

The Formula

Electrical Power = Lumens / Efficacy (Watts)

Annual Energy & Cost: kWh = (Watts hours 365) / 1000

Worked Example

A homeowner replacing ten 60W incandescent light bulbs (800 lumens each) with 8W LEDs calculates their total lighting power drops from 600W to 80W, saving approximately 150 per year on electricity bills.

Understanding Your Result

Unit conversion precision: round to the same number of significant figures as your original measurement. Converting 6 feet to meters gives 1.8288 m — but if your measurement was approximate (±1 inch), expressing more than 2 decimal places is false precision. For international trade and technical specifications, SI units (meters, kilograms, liters) are the standard. US customary units (feet, pounds, gallons) differ from Imperial UK units: 1 US gallon = 3.785 L vs. 1 UK gallon = 4.546 L.