Why lumens and watts aren’t the same thing
Watt (W) is electrical power. Lumen (lm) is visible light output. Two lamps with the same wattage can produce very different lumen levels depending on their efficiency (lm/W).
Formulas
watts = lumens ÷ (lumens per watt)
lumens = watts × (lumens per watt)
Example: 1,200 lm with LED 100 lm/W:
watts = 1200 ÷ 100 = 12 W
Typical efficacies (rule of thumb)
- Incandescent: 10–15 lm/W
- Halogen: 15–20 lm/W
- CFL: 60–75 lm/W
- LED household: 80–110 lm/W
- Good LED panel/strip: 110–130 lm/W
FAQ
1. How many watts is 800 lumens?
At 100 lm/W (typical LED), 800 ÷ 100 = 8 W.
2. How many lumens is a 10W LED?
10 × 100 = 1,000 lm if it’s a decent LED. Use your real fixture’s lm/W for a better number.
3. Can I use this for outdoor lighting?
Yes — pick the LED value closest to your product datasheet, or enter custom lm/W.
Formula (LaTeX) + variables + units
This section shows the formulas used by the calculator engine, plus variable definitions and units.
Formula (extracted LaTeX)
\[','\\]
','\
Formula (extracted text)
watts = lumens ÷ (lumens per watt) lumens = watts × (lumens per watt) Example: 1,200 lm with LED 100 lm/W: watts = 1200 ÷ 100 = 12 W
Variables and units
- No variables provided in audit spec.
Sources (authoritative):
- NIST — Weights and measures — nist.gov · Accessed 2026-01-19
https://www.nist.gov/pml/weights-and-measures - NIST — SI units — nist.gov · Accessed 2026-01-19
https://www.nist.gov/pml/owm/metric-si/si-units
Changelog
Version: 0.1.0-draft
Last code update: 2026-01-19
Last code update: 2026-01-19
0.1.0-draft · 2026-01-19
- Initial audit spec draft generated from HTML extraction (review required).
- Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
- Confirm sources are authoritative and relevant to the calculator methodology.