LED Wattage and Lumens Calculator
Convert lumens to watts, size any commercial space to IES light levels, and see your energy savings, payback, and CO2 reduction. Then get a free fixture plan from our team.
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Why LED wattage and lumen conversion matters
For decades you could pick a fixture by watts, because with metal halide, HPS, and fluorescent the wattage roughly tracked brightness. LED breaks that link. A 150-watt LED high bay can out-light a 400-watt metal halide, so sizing a project by the old wattage leads to over-buying fixtures and over-lighting the space. The number that actually matters is lumens, the light delivered to the work surface. This calculator converts between lumens and watts correctly, sizes your space to the recommended light level, and shows the energy, dollars, and CO2 you save by switching. See the methodology.
Go Green LED International supplies commercial and industrial LED fixtures from US inventory with a 5-year fixture warranty. Each product page states that model's safety listing, ETL or UL, and its DLC level.
Lighting Calculator
How Many Lumens Do You Need?
Size your space to IES light-level targets, or find the LED that replaces your old fixture. Then get a free fixture plan from our team.
Estimates based on IES recommended light levels. We confirm the exact layout with a free photometric plan.
Methodology
How the calculator works
The formulas in plain terms, so you can check the math.
Lumens vs watts
Watts measure the power a fixture draws. Lumens measure the light it produces. Two fixtures can draw the same watts and produce very different light, which is why you size by lumens, not watts.
What is LED efficacy, in lumens per watt?
Efficacy is lumens divided by watts, the light a fixture delivers for the power it draws. Go Green LED fixtures run from 125 to 170 lumens per watt on their spec sheets: the GGL-AR09 area light reaches 170 lm/W, the GGL-LHB10 linear high bay 160 lm/W, the GGL-UFO12 UFO high bay 145 lm/W and the GGL-ALT8 T8 tube 135 lm/W. To size a fixture, divide the lumens a space needs by the efficacy, watts = lumens needed / efficacy: 21,000 lumens at 140 lm/W is a 150 W fixture. Higher efficacy means fewer watts, and a smaller electricity bill, for the same light on the floor. Figures from the product spec sheets.
How many lumens does a space need?
One foot-candle equals one lumen per square foot, so lumens needed = floor area (sq ft) x target foot-candles for the work done there. The IES recommended levels this calculator uses are 20 to 30 fc for warehouse storage, 30 to 50 fc for offices and manufacturing, 50 to 100 fc for retail, about 50 fc for a service bay and 1 to 5 fc for a parking lot. A 10,000 sq ft warehouse at 25 fc needs 250,000 lumens at the floor. Fixtures lose light to dirt, ageing and mounting height before it reaches the floor, so the calculator adds a light-loss allowance that grows with ceiling height and, past about 20 feet, moves the estimate to high bay fixtures.
Energy cost and savings
Annual cost = fixtures x watts / 1000 x hours per day x days per year x rate ($/kWh). Savings is the old annual cost minus the new. We adjust the old fixture's draw for ballast losses (metal halide adds about 15%, HPS 13%, fluorescent 10%) so the comparison is honest.
How is the annual saving of an LED retrofit calculated?
Annual saving = (old system watts minus new watts) x fixtures / 1,000 x hours a day x days a year x rate ($/kWh). The old side includes the ballast: metal halide adds about 15% to lamp wattage, HPS 13%, fluorescent 10%. Example: 100 fixtures of 400 W metal halide (460 W with ballast) replaced by 150 W LED, 12 hours a day, 6 days a week, at $0.13 per kWh: 31 kW saved x 3,744 hours = 116,000 kWh and about $15,000 a year, before any utility rebate. Simple payback is the net project cost divided by that figure.
CO2 reduction
CO2 avoided = kWh saved x 0.855 lb/kWh (US average delivered grid, EIA and EPA), converted to metric tons.
Why LED drivers affect wattage
Every LED fixture has a driver that consumes a little power, just as the old fixtures had a ballast. We size to the real system wattage, not just the bare LED rating, so the equivalents and savings are not overstated.
Reference
LED wattage conversion chart
Typical wattage that produces a given light output, by technology. Approximate, for quick comparison.
| Light output (lumens) | LED watts | Fluorescent watts | Metal halide / HPS watts |
|---|---|---|---|
| ~5,000 | 35 to 45 W | ~100 W | 100 to 150 W |
| ~10,000 | 75 to 90 W | ~200 W | 175 to 250 W |
| ~16,500 | 120 to 150 W | ~320 W | 250 to 400 W |
| ~24,000 | 175 to 200 W | n/a | ~400 W |
| ~33,000 | 240 W | n/a | ~750 W |
| ~45,000 | 300 W | n/a | ~1,000 W |
Approximate equivalents assuming LED around 120 lm/W, fluorescent around 50 lm/W, and typical HID output before depreciation. Real numbers vary by fixture, optics, and age. Use the calculator above for your exact fixture and rate.
Quick Answers
Common conversions and light-level targets
The conversions we are asked about most, in one place. Use the calculator above for your exact space.
Metal halide and HPS to LED
- 1000W metal halide~300W LED
- 400W metal halide~150W LED
- 250W metal halide / HPS~100W LED
- 150W metal halide~60W LED
A 400W metal halide draws about 460W with its ballast; a 150W LED high bay matches its light and cuts energy roughly two thirds. Approximate, confirm with the calculator.
What LED wattage replaces a 400 W metal halide?
A 150 W LED high bay replaces a 400 W metal halide in most warehouses. The metal halide draws about 460 W once its ballast is counted, and its output falls through its life; a GGL-UFO12 set to 150 W delivers 21,000 lumens from the first hour and holds it. The swap cuts the fixture's energy use by about two thirds: 310 W saved per fixture, or about 1,360 kWh a year at 12 hours a day. For a 1,000 W metal halide a 300 W LED is the usual replacement, for 250 W a 100 W. Confirm the count and spacing with a photometric layout rather than matching wattage alone. Figures from the GGL-UFO12 spec sheet.
Lumens per square foot by space
- Warehouse / storage20 to 30
- Office / manufacturing30 to 50
- Retail50 to 100
- Auto / service bay~50
- Parking lot1 to 5
One foot-candle equals one lumen per square foot, so a 30 fc office target is 30 lumens per square foot of floor.
Savings by Industry
What a switch looks like in real spaces
Example retrofits at $0.13/kWh. Your numbers depend on rate, hours, and fixture count, which the calculator works out for you.
Warehouse
100 x 400W metal halide high bays to 150W LED, 12 hours a day. Roughly $15,000 saved per year and about 116,000 kWh, payback in about 16 months.
Office
75 x 4-lamp fluorescent troffers (128W) to 40W LED panels, 10 hours a day. Roughly $2,600 saved per year, payback in about 2.5 years, with better, flicker-free light.
Retail
40 x 250W metal halide to 80W LED, 14 hours a day. Roughly $5,400 saved per year, payback in about 13 months, plus higher color rendering on merchandise.
Parking lot and exterior
20 x 400W metal halide shoebox to 150W LED area lights, dusk to dawn. Roughly $3,200 saved per year, payback in about 1.8 years, with dark-sky-friendly optics.
Customer Results
Real savings from real switches
A sample of what businesses saved in their first year after moving to Go Green LED.
Results vary by facility size, operating hours, and utility rate. Use the calculator above to estimate yours.
The Real Story
Why lumens matter more than watts
LED efficiency. A modern LED turns far more of its watts into usable light than metal halide or fluorescent, so it hits the same light level on a fraction of the power.
Color temperature. A 5000K fixture reads brighter and crisper than a warm 3000K one at the same lumens. The right CCT can let you use less light, not more.
Beam angle. A focused beam puts more of the lumens where you need them. A wide flood spreads the same lumens thinner, so raw lumens alone do not tell the whole story.
Fixture optics. Lenses and reflectors decide how many lumens actually land on the floor instead of scattering. Good optics are why a lower-lumen LED can out-perform a higher-lumen fixture on paper.
For high ceilings, start with our LED high bays. For offices and interiors, see LED troffers and panels.
Common Questions
Lumens, watts, and savings FAQ
How do I convert lumens to watts?
How many lumens do I need for a warehouse?
How much can I save switching to LED?
What is the lifespan of LED fixtures?
Do LEDs reduce heat output?
What LED wattage replaces a 400-watt metal halide?
How many lumens per square foot do I need?
See what your space needs.
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