Lumens to Watts Calculator

Lumens to Watts Calculator. Lumens measure how bright a light bulb is, but watts tell you how much electricity it uses — and the two aren't directly interchangeable across bulb types. Enter your luminous flux in lumens and select your bulb type (Incandescent, Halogen, CFL, LED, or a custom efficacy value) into the Lumens to Watts Calculator to get the estimated power consumption in watts. Secondary outputs include the luminous efficacy used and an estimated annual electricity cost based on 3 hours of daily use at $0.12/kWh. Also try the use the Lighting Layout Calculator.

Luminous Flux (Lumens) *

Amount of visible light emitted by the bulb

Bulb Type *

Custom Luminous Efficacy

lm/W

Only used when 'Custom Efficacy' is selected above

Results

Power Consumption

Luminous Efficacy Used

Estimated Annual Cost (3hrs/day @ $0.12/kWh)

Results Table

How are lumens different from watts?

Lumens measure the brightness of light output, while watts measure electrical power consumption. A higher lumen count means brighter light, while higher watts mean more energy used. See also our Lighting Calculator.

What is the (lm/W) figure?

Luminous efficacy (lm/W) measures how efficiently a bulb converts electrical power into visible light. LED bulbs typically achieve 80-100 lm/W, while incandescent bulbs only reach 12-18 lm/W.

What wattage light bulb do I need?

Focus on lumens for brightness needs, not watts. For example, 800 lumens (equivalent to old 60W incandescent) requires only 8-10W with LED technology.

How do I calculate watts from lumens?

Use the formula: Watts = Lumens ÷ Luminous Efficacy (lm/W). For example, 800 lumens ÷ 90 lm/W = 8.9 watts for an LED bulb.

Why are LED bulbs more efficient than incandescent?

LED bulbs convert most electrical energy directly into light, while incandescent bulbs waste about 90% of energy as heat. This makes LEDs 5-6 times more efficient.

What lumens do I need for different rooms?

Living rooms need 1500-3000 lumens, bedrooms 1000-2000 lumens, kitchens 3000-4000 lumens, and bathrooms 2000-3000 lumens depending on room size.

How much money can I save switching to LED?

LED bulbs use 75-80% less energy than incandescent bulbs. A 60W equivalent LED (9W actual) can save $50+ per year compared to incandescent when used 3 hours daily. You might also find our use the Emergency Lighting Calculator useful.