Light & running cost
Use a measured or clearly documented PPFD at the leaves. Watts are for the electricity calculation.
Your calculation
Enter your measurements and choose Calculate.
What the result means
DLI = PPFD × daily hours × 0.0036. This assumes the entered PPFD stays constant through those hours. A single window reading does not describe changing daylight.
Energy in kWh = actual watts × hours × days ÷ 1,000. Cost = energy × your electricity rate. Equivalent-watt labels, other equipment and fixed utility charges are excluded.
The example values are illustrative, not a recommended plant setting. This calculator does not supply a species-specific optimum or a flowering schedule.
Measurement definitions: Iowa State Extension ↗