Lumens to Watts Converter — Free Online Calculator
Convert lumens to watts for LED, CFL, and incandescent bulbs. Find the right wattage equivalent for any brightness.
How to Use This Calculator
Enter the brightness you need in lumens. The calculator shows the wattage required for each bulb type.
The Formula Explained
LED: ~90 lumens/watt. CFL: ~60 lm/W. Incandescent: ~14 lm/W. Halogen: ~20 lm/W.
The End of the Incandescent Era
Until the early 2000s, light bulbs were rated by wattage because all household bulbs were incandescent and watts were a reasonable proxy for brightness. A 60W bulb was always brighter than a 40W bulb, period. That universe ended with the rise of fluorescent and LED lighting, which decoupled power consumption from light output. A modern 9-watt LED produces more light than a 60-watt incandescent. Power ratings became meaningless for comparing brightness; lumens became the new standard.
The FTC Lighting Facts label (required on US consumer bulbs since 2012) centers on lumens as the primary brightness metric, with watts listed as a secondary energy-use number. This confused consumers for years because everyone grew up thinking in watts. The lumens-to-watts conversion calculator bridges the old and new thinking: enter lumens, get estimated watts for each bulb technology. Useful for retrofit projects and comparing across bulb types.
Worked Example: Kitchen Lighting Retrofit
A kitchen currently has 6 recessed cans with 65-watt BR30 incandescent bulbs, total power draw 390 watts. Each bulb produces about 750 lumens, total kitchen illumination 4,500 lumens. Replace with LED BR30 bulbs rated 800 lumens each at 10 watts, total 60 watts. The lumen output actually increases slightly (4,800 vs 4,500) while power drops from 390 to 60 watts — 85% energy reduction.
Annual savings at 4 hours per day average use: old = 390 × 4 × 365 / 1000 = 569 kWh. New = 60 × 4 × 365 / 1000 = 87 kWh. Savings: 482 kWh per year. At typical US residential rate of 16 cents per kWh, that is 77 USD per year savings. LED bulbs cost about 8 USD each times 6 bulbs = 48 USD. Payback: about 8 months. After that, pure savings for the remaining 20+ year life of the LEDs.
Worked Example: Commercial Warehouse Relamping
A 10,000 square foot warehouse has 40 high-bay 400-watt metal halide fixtures (each producing about 36,000 lumens at 90 lm/W). Total power: 16,000 watts, total lumens: 1,440,000. Replace with 150W LED high-bays at 22,500 lumens each (150 lm/W). To match total lumens, need 1,440,000 / 22,500 = 64 fixtures. But warehouse lighting is typically oversized; 40 LED fixtures at 22,500 lumens = 900,000 lumens, which actually provides better uniformity than the metal halides (900,000 on working surfaces is more useful than 1,440,000 including wasted overspill).
Power savings: 16,000W to 6,000W = 10,000 watts saved. At 12 hours daily operation, 6 days per week: 10,000 × 12 × 6 × 52 / 1000 = 37,440 kWh saved annually. At 10 cents per kWh commercial rate, that is 3,744 USD per year. LED fixtures at 300 USD each = 12,000 USD. Payback: 3.2 years. Plus reduced maintenance costs (LEDs last 50,000+ hours vs 15,000 for metal halide).
Common Lumens-to-Watts Mistakes
1. Comparing LED wattage to incandescent watts directly. A 10W LED and a 10W incandescent produce vastly different amounts of light. Always compare lumens to lumens, not watts to watts, when evaluating replacements.
2. Ignoring color temperature. 2700K LED and 5000K LED at the same wattage produce similar lumens, but appearance is completely different (warm vs cold). Kitchen counters work better at 3000-4000K, bedrooms at 2700K, task lighting at 4000-5000K.
3. Forgetting CRI. Two LED bulbs with identical lumens and color temperature can look completely different if one has CRI 80 and the other CRI 95. CRI 90+ is noticeably better for residential use. CRI 80 is acceptable for general commercial, parking lots, and warehouses where color accuracy does not matter.
4. Trusting cheap LED lumen ratings. Bargain bin LEDs often overstate lumens by 20-30% on the package. Look for ENERGY STAR certification or UL-verified ratings for accurate numbers.
5. Using lumens when lux is the right metric. Lumens measure total light output from a bulb. Lux (or foot-candles) measures light falling on a surface, which depends on bulb lumens, distance, fixture optics, and reflectivity. Task lighting specs use lux; bulb ratings use lumens.
Luminous Efficacy by Bulb Type
Incandescent (standard): 10-17 lumens per watt. Halogen: 16-24 lm/W. Compact fluorescent (CFL): 50-70 lm/W. Linear fluorescent (T8, T5): 80-105 lm/W. Metal halide: 65-115 lm/W. High-pressure sodium: 100-150 lm/W (but poor color). Mercury vapor: 35-65 lm/W (obsolete). LED (residential): 70-120 lm/W. LED (commercial high-end): 140-180 lm/W. Laboratory LED records: 200+ lm/W.
Typical equivalence for common bulb sizes: 40W incandescent = 450 lumens ≈ 4-6W LED. 60W incandescent = 800 lumens ≈ 8-10W LED. 75W incandescent = 1,100 lumens ≈ 11-13W LED. 100W incandescent = 1,600 lumens ≈ 15-18W LED. 150W incandescent = 2,600 lumens ≈ 24-28W LED.
Lighting Standards and References
ENERGY STAR certification requires LEDs to meet minimum lumens-per-watt thresholds and verified lumen ratings. DLC (DesignLights Consortium) is the commercial equivalent for fixtures. UL 1993 covers safety standards for LED lamps. IES (Illuminating Engineering Society) publishes recommended light levels for different tasks and spaces.
For specifications: IES Handbook gives target lux levels for every common space type (residential rooms, offices, warehouses, surgical suites). FTC Lighting Facts label format is defined in 16 CFR 305. California Title 24 drives lighting efficiency requirements in new construction and retrofits, with minimum lumens-per-watt thresholds that effectively require LED in most applications.
Lumens to watts: bulb efficacy across technologies
Lumens measure light output; watts measure electrical input. Their ratio (lumens per watt, or lm/W) is called luminous efficacy and varies dramatically by technology. The calculator above gives wattage for a target lumen output across incandescent, halogen, CFL, and LED, plus the comparative wattage savings.
The formula and what it does
Efficacy ranges: incandescent 10-15 lm/W, halogen 15-20, CFL 50-70, LED 80-120 (typical) or up to 200 for high-efficacy commercial LEDs. So a 800-lumen output light: incandescent 60 W, halogen 43 W, CFL 14 W, LED 9 W typical or as low as 4 W for premium fixtures.
Worked example
Scenario: Retrofit a 4-lamp 4-foot T8 fluorescent fixture (10,400 lumens total at 32 W each = 128 W) with LED. Find LED wattage needed and savings.
At LED efficacy 130 lm/W, the same 10,400 lumens requires 80 W. Savings: 48 W per fixture. Over a 50-fixture office on 12 hr/day x 250 days/year: 48 W x 50 x 12 x 250 / 1000 = 7,200 kWh saved per year. At 12 cents/kWh: $864/year per office. Payback on a $50 LED retrofit per fixture: about 2.9 years before utility rebates.
Common mistakes to avoid
undefinedFrequently asked questions
Why is LED efficacy higher than other technologies?
LEDs produce light by electron-hole recombination in a semiconductor junction, which is intrinsically efficient. Incandescents waste 90 percent of energy as heat. CFLs waste 50-60 percent on phosphor conversion and ballast losses.
What about the color-quality tradeoff?
High-efficacy LEDs sometimes have lower CRI (color rendering index). Top-tier residential LEDs hit 90+ CRI at 100 lm/W. Commercial high-bay fixtures aim for 80 CRI and 150+ lm/W.
Does dimming affect efficacy?
LED dimming retains efficacy fairly well (within 10 percent). Incandescent dimming kills efficacy fast: a 50 percent dimmed incandescent uses 80 percent of full power for 30 percent of light output.
How long do LEDs last?
Quality LEDs are rated L70 at 25,000-50,000 hours, meaning they retain 70 percent of initial output at that time. That is 17-34 years at 4 hours/day. Cheap LEDs fall short of this due to inadequate thermal management.
Why do some LED bulbs say 60 W equivalent at 9 W?
It is a marketing convention. 800 lumens has been the de-facto 60 W incandescent equivalent since EnergyStar 2008. The actual LED wattage to hit 800 lm varies from 7-11 W across manufacturers.
How does this affect HVAC sizing?
LEDs reject far less heat to the conditioned space. A commercial office switching from fluorescent to LED can downsize cooling by 5-10 percent because the lighting load disappears. ASHRAE Manual J catches this on rigorous designs.