How to use the calculator
- Select whether you want to convert from lumens to watts or from watts to lumens.
- Pick a bulb type (LED, CFL, halogen, or standard incandescent) to load a representative luminous efficacy, or select “My own bulb” and enter the value from its Lighting Facts label (lumens ÷ watts).
- Enter the light output or power value and click Calculate.
- Use the Copy Result button to copy the exact figures and technology comparisons to your clipboard.
Formula and conversion principles
watts = lumens ÷ luminous efficacy (lm/W) | lumens = watts × luminous efficacy (lm/W)
Luminous efficacy (measured in lm/W) describes how effectively a light source converts electrical power into human-visible light flux. Because solid-state LEDs produce far less waste heat than thermal filament or fluorescent gas bulbs, they yield substantially higher efficacy.
The standard incandescent equivalence interpolates linearly between points of the U.S. Department of Energy benchmark (450 to 1,600 lumens).
Energy efficiency comparison: LED vs CFL vs incandescent
Luminous efficacy (lumens per watt) determines how much electrical energy is converted into visible illumination rather than wasted heat. Below is an energy efficiency comparison across modern LED, Compact Fluorescent (CFL), halogen, and traditional incandescent bulbs based on U.S. Department of Energy (DOE) and FTC benchmarks:
| Bulb Technology | Luminous Efficacy | 450 lm (~40W) | 800 lm (~60W) | 1,100 lm (~75W) | 1,600 lm (~100W) | Typical Lifespan | Energy Savings |
|---|---|---|---|---|---|---|---|
| LED (Light Emitting Diode) | 80–120 lm/W (typ. 90) | ~5 W | ~8.9 W | ~12 W | ~16 W | 15,000–25,000 hrs | ~85% savings |
| CFL (Compact Fluorescent) | 50–70 lm/W (typ. 57) | ~8 W | ~14 W | ~19 W | ~25 W | 8,000–10,000 hrs | ~75% savings |
| Halogen (Incandescent) | 16–22 lm/W (typ. 17.4) | ~26 W | ~43 W | ~63 W | ~92 W | 1,000–2,000 hrs | ~28% savings |
| Standard Incandescent | 12–16 lm/W (typ. 13.3) | 40 W | 60 W | 75 W | 100 W | 750–1,000 hrs | Baseline (0%) |
Figures are based on U.S. Federal Trade Commission (FTC) lighting facts (FTC consumer advice) and U.S. Department of Energy guidelines (DOE Energy Saver). Actual bulb efficacy varies by manufacturer, driver design, and color temperature.
Two-way workflow: sizing bulbs with Room Lux Calculator
Sources: efficacy values used
| Bulb type | Example efficacy | Based on |
|---|---|---|
| LED | 88.9 lm/W | an LED bulb giving about 800 lm at about 9 W: U.S. Federal Trade Commission, Consumer Advice: “Shopping for Light Bulbs” (checked 15 October 2026) |
| CFL (compact fluorescent) | 57.1 lm/W | a CFL bulb giving about 800 lm at about 14 W: U.S. Federal Trade Commission, Consumer Advice: “Shopping for Light Bulbs” (checked 15 October 2026) |
| Halogen (incandescent) | 17.4 lm/W | a 43 W halogen bulb rated at 750 lm: Signify (Philips) product sheet for a 43 W A19 halogen lamp: 750 lm nominal flux, “wattage equivalent 60 W” (checked 15 October 2026) |
| Standard incandescent | 13.3 lm/W | a 60 W incandescent bulb giving about 800 lm: U.S. Department of Energy, Energy Saver: “Lumens and the Lighting Facts Label” (rule of thumb for replacing incandescent bulbs) |
U.S. Department of Energy rule of thumb for replacing standard incandescent bulbs (U.S. Department of Energy, Energy Saver: “Lumens and the Lighting Facts Label” (rule of thumb for replacing incandescent bulbs)):
| Incandescent bulb | Look for about |
|---|---|
| 40 W | 450 lm |
| 60 W | 800 lm |
| 75 W | 1,100 lm |
| 100 W | 1,600 lm |
Units
Power in watts (W), light output in lumens (lm), efficacy in lumens per watt (lm/W).
Limits of this converter
- The example efficacies come from representative industry reference points. Real LED, CFL, halogen and incandescent bulbs vary; the lumens and watts stated on your bulb’s packaging are always the authoritative figures.
- Lumens represent total omnidirectional luminous flux. They do not indicate beam angle, Correlated Color Temperature (CCT), or Color Rendering Index (CRI), so two bulbs with identical lumen ratings can produce different visual environments.
- For LED fixtures with an external driver or transformer, check whether the rated wattage reflects lamp draw or total system power draw.
- Automotive headlamps are subject to separate vehicle lighting standards and regulations; verify automotive replacement bulbs against your vehicle owner manual.
Frequently asked questions
How do I convert lumens to watts for an LED bulb?
Divide the lumens you need by the bulb’s luminous efficacy in lumens per watt (watts = lumens ÷ lm/W). For example, to get 800 lumens from a typical 90 lm/W LED bulb, you need 800 ÷ 90 ≈ 8.9 watts. Always check the rated lumens and wattage printed on the bulb’s packaging for the true figure.
How many lumens is a 60-watt incandescent bulb equivalent to in LED?
Under U.S. Department of Energy (DOE) benchmarks, a traditional 60-watt incandescent bulb produces approximately 800 lumens. A modern energy-efficient LED bulb produces that same 800 lumens using only about 8 to 9 watts, saving over 85% in electrical power.
What is the difference between lumens and watts in lighting?
Watts measure the electrical power consumed by a light bulb, while lumens measure the visible light output (luminous flux) emitted by the bulb. Modern lighting separates power consumption from brightness because LED, CFL, and incandescent bulbs convert electricity to light with very different efficiencies.
What is luminous efficacy and why does it vary by bulb type?
Luminous efficacy indicates how efficiently a light source converts electrical energy into visible light, expressed in lumens per watt (lm/W). Standard incandescent bulbs offer low efficacy (10–17 lm/W) because most energy is wasted as heat. CFLs achieve 50–70 lm/W, while modern LEDs deliver 80–120+ lm/W.
How do I know the exact efficacy of my own light bulb?
Check the Lighting Facts label on the bulb’s retail box. Divide the stated light output in lumens by the power consumption in watts (efficacy = lumens ÷ watts). In this calculator, select “My own bulb” and enter that figure for the most accurate calculation.
Can I replace an incandescent bulb with a higher-lumen LED in the same fixture?
Yes, provided the actual electrical wattage drawn by the LED bulb does not exceed the fixture’s maximum rated wattage. Because LEDs consume 80% to 85% fewer watts for the same lumens, you can safely achieve significantly brighter illumination without overloading the socket.
Articles about this calculator
- Watts to Lumens: Practical Energy-Saving LED Lighting Guide
- LED Fixture Lumens Guide: Energy-Efficient Home Lighting