How long should I run my grow light?
Grow-light runtime and daily-light planner
Get a practical daily runtime range for your plant type.
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How to use this estimate
Enter plant type, leaf-height brightness, and any natural light, then calculate daily runtime. After you get a hour range, place those hours on a timer with a turn-on time.
Common mistakes
- Running lights so long that plants never get a dark rest period
- Using wattage alone as if it equaled leaf-level brightness
- Ignoring natural light already reaching the plant
- Treating a midpoint hour count as an exact biological requirement
Assumptions at a glance
Last reviewed with the calculator formula set on 2026-07-23. Estimates stay range-based on purpose.
Key sources and methodology details
- Daily Light Integral from PPFD and photoperiod — University of New Hampshire Extension. Reviewed 2026-07-26. https://extension.unh.edu/resource/supplemental-lighting-run-time-worksheet
- Indoor plant light category DLI planning ranges — University of New Hampshire Extension (synthesized planning bands). Reviewed 2026-07-26. https://extension.unh.edu/blog/2021/02/optimizing-plant-growth-indoor-lighting-qa
- User-estimated natural-light DLI contribution — Plant Light Planner (user input). Reviewed 2026-07-26. https://extension.unh.edu/resource/supplemental-lighting-run-time-worksheet
Full portfolio methodology: Methodology
Related planners
EnergyWhat will my grow light cost?See daily and monthly operating cost for your fixtures and schedule.PlacementHow high should I hang my grow light?See which hanging height fits your plants best.SchedulePlan lighting for seedlings and herbsBuild a grow-light schedule aimed at seedlings or culinary herbs.
