About the Lumens to Watts
The Lumens to Watts Equivalent Converter estimates how many watts a bulb needs to draw to produce a target brightness, based on typical luminous efficacy for incandescent, CFL, and LED technology. It's aimed at anyone replacing an old incandescent bulb with an LED or CFL and trying to figure out what wattage rating actually matches the old bulb's light output.
How It Works
Enter the desired brightness in lumens and choose a bulb type; the calculator divides lumens by that bulb type's typical efficacy figure, 15 lm/W for incandescent, 60 lm/W for CFL, or 85 lm/W for LED, to estimate the wattage needed. It falls back to the LED efficacy figure if an unrecognized bulb type is ever submitted.
Examples
Replacing an old 100W incandescent bulb
A 1,600-lumen target with incandescent selected returns about 107 W (1600 / 15), roughly matching a traditional 100W bulb's real-world output.
Finding the LED equivalent for 800 lumens
The default 800-lumen, LED-selected input returns about 9 W (800 / 85), showing how much less power an LED needs to match the incandescent bulb's brightness in the example above.
Advantages
- Lets you compare bulb wattage needs across three lighting technologies using a single lumen target.
- Makes it easy to see why LED replacements are rated so much lower in watts than the bulbs they replace.
- Defaults sensibly to LED efficacy, the most common modern reference point, if a bulb type is missing.
Common Mistakes
- Assuming a bulb marketed as a "60W equivalent" LED actually draws close to 60 watts, when it's typically closer to 8 to 10 watts.
- Comparing wattage estimates across bulb types without also checking color temperature or beam angle, which affect perceived brightness.
- Using an old incandescent wattage number directly as a lumen target instead of first converting it to lumens.
Edge Cases to Watch For
- The efficacy values are fixed averages for each bulb category; actual products vary, so the result is an estimate rather than an exact match to any specific bulb's packaging rating.
- Because efficacy differs so much by technology, the same lumen target produces very different wattage estimates depending only on which bulb type is selected, not on the brightness itself.
- Wattage is rounded to the nearest whole number, which can matter when comparing two closely rated bulbs.
Common Use Cases
- Homeowners shopping for LED or CFL replacements and translating an old bulb's wattage into an equivalent brightness target.
- Interior designers and lighting planners estimating total wattage load for a room lit entirely with one bulb technology.
- DIYers building custom fixtures who need to size a power supply based on a desired lumen output.