Lumens to Watts Calculator
Use our lumens to watts calculator to find out how much power a light bulb needs to produce a given amount of brightness — or do the reverse. Enter any two values (brightness, power, or efficacy) to instantly calculate the third.
How to Use This Calculator
Select one of three calculation modes:
- Lumens → Watts — Enter the desired brightness (lumens) and the luminous efficacy (lm/W) of the bulb to find out how many watts are required.
- Watts → Lumens — Enter the power consumption (watts) and efficacy to find how many lumens the bulb produces.
- Find Efficacy — Enter both lumens and watts to calculate the bulb's luminous efficacy.
Use the Bulb Type Preset dropdown to auto-fill the typical luminous efficacy for LED, CFL, halogen, incandescent, and other bulb types.
Lumens to Watts Formula
The relationship between brightness (lumens), power (watts), and luminous efficacy is:
P (W) = Φ (lm) ÷ η (lm/W)
Where:
- P — power consumed by the bulb in watts (W)
- Φ — luminous flux, i.e. the total light output in lumens (lm)
- η — luminous efficacy in lumens per watt (lm/W) — how efficiently the bulb converts electrical power into visible light
Example: An LED bulb with an efficacy of 100 lm/W producing 1,200 lumens consumes:
P = 1,200 ÷ 100 = 12 W
Light Bulb Efficiency Comparison Chart
The table below shows typical luminous efficacy ranges for common light bulb types. Higher efficacy means more light per watt — and lower electricity bills.
| Bulb Type | Luminous Efficacy (lm/W) | Equivalent to 60 W Incandescent |
|---|---|---|
| LED | 80–120 | ~8–10 W |
| Compact Fluorescent (CFL) | 45–75 | ~13–15 W |
| Fluorescent Tube | 40–105 | ~14–18 W |
| High-Pressure Sodium (HPS) | 85–150 | ~9–11 W |
| Low-Pressure Sodium (LPS) | 100–190 | ~7–9 W |
| Metal Halide | 75–100 | ~11–13 W |
| Halogen | 16–30 | ~38–50 W |
| Incandescent (Tungsten) | 12–18 | 60 W (baseline) |
Note: Efficacy values are typical mid-range figures. Actual values vary by manufacturer and model.
What Are Lumens?
A lumen (lm) is the SI unit of luminous flux — the total amount of visible light emitted by a source in all directions. Common light output benchmarks:
- 400–500 lm — soft reading light (equivalent to a 40 W incandescent)
- 700–900 lm — standard room lighting (equivalent to a 60 W incandescent)
- 1,100–1,300 lm — bright overhead light (equivalent to a 75–100 W incandescent)
- 1,600+ lm — workshop or high-intensity lighting
What Are Nits?
A nit is a measure of luminance (brightness per unit area) used for displays: monitors, smartphones, and TVs. One nit equals one candela per square meter (cd/m²). The sun at noon measures about 1.6 billion nits. Unlike lumens — which describe total light output — nits measure how bright a surface appears from a given direction.
American vs. Metric Light Measurement Units
Both the American (imperial) and metric systems use lumens and watts — these are universal SI units. However, illuminance (how much light falls on a surface) is measured differently:
- Metric: lux (lx) — lumens per square meter (lm/m²)
- American: foot-candles (fc) — lumens per square foot (lm/ft²)
Conversion: 1 foot-candle = 10.764 lux. Use our Lighting Calculator to work with illuminance levels in both systems.
How to Compare LED to Incandescent Bulbs
To replace a 60 W incandescent bulb (producing ~800 lm) with an LED:
- Find the lumens of your current bulb (printed on the packaging): e.g. 800 lm
- Use Lumens → Watts mode
- Select LED as the bulb type preset (100 lm/W typical efficacy)
- Result: 800 ÷ 100 = 8 W LED
That's an 87% reduction in power consumption for the same brightness.
Electricity Cost Estimation
Enable the Electricity Cost option in the calculator to estimate how much it costs to run your bulb annually. Enter:
- Hours per day — how many hours the light is on each day
- Days per year — typically 365
- Electricity rate — your local rate per kWh (check your electricity bill)
- Currency — USD, RUB, EUR, GBP, and 9 other world currencies supported
The calculator will show your daily, monthly, and annual electricity cost for that bulb.
Frequently Asked Questions
How many lumens is a 60-watt bulb?
A standard 60 W incandescent bulb produces approximately 800 lumens, giving an efficacy of about 13.3 lm/W.
How many watts is 1000 lumens?
It depends on the bulb type. For an LED (100 lm/W): 10 W. For a CFL (60 lm/W): ~16.7 W. For an incandescent (15 lm/W): ~66.7 W.
Is higher lumens per watt better?
Yes — higher luminous efficacy means the bulb produces more light per unit of electrical energy consumed, making it more efficient and cheaper to run.
What wattage LED replaces a 100-watt incandescent?
A 100 W incandescent produces about 1,600 lumens. An LED with 100 lm/W efficacy needs only 16 W to produce the same brightness.