How to use this Light Distance tool
Set your options in the calculator above, read the result, then verify with a calibrated meter when the decision matters. Bookmark this page for reservoir day — consistent units beat copying numbers from charts that never name their scale or bottle rate.
Formula reference
Planning band scales roughly with √(watts/100) from crop baselines
Distance is intensity control
Moving a light closer raises PPFD under the center and shrinks the even footprint. Raising it softens intensity and widens coverage. Dimmer knobs do the same job with less geometry change — use both.
This tool gives a starting hang range from draw watts and crop class. Optics and efficacy differ by brand, so treat manufacturer PPFD maps as the tie-breaker.
Leafy greens vs fruiting crops
Lettuce often wants roughly 200–400 µmol/m²/s. Tomato and pepper canopies often want more. Running a fruiting chart over butterhead is a classic tip-burn setup.
Seedlings need gentler light. Start high or heavily dimmed, then lower over a few days as plants toughen.
What to watch after you hang the light
Bleached tops, cupped leaves, or crispy margins: raise or dim. Stretching with pale stems: lower slightly or add hours. Measure corners, not only the hotspot.
Pair hang height with a DLI check — long photoperiods at modest PPFD can still hit leafy daily targets without cooking the canopy.
Frequently asked questions
How far should an LED be from lettuce?
Often somewhere in the 12–24 inch band for mid-power panels, but wattage and dimming matter. Start higher, then lower until growth is compact without bleaching.
Is wattage accurate enough?
It is a planning proxy only. Two 100 W lights can differ in spread and efficiency. Use this for first hang, then refine with a meter or vendor chart.
Related calculators
- Grow Light Coverage & Distance Calculator — Plan grow light coverage and hanging distance from wattage and height for leafy greens and indoor tents.
- DLI Calculator — Free PPFD Tool — Calculate Daily Light Integral from PPFD and your light schedule to optimise photosynthesis.
- Humidity Calculator — Get recommended humidity and VPD ranges based on your plant growth stage and leaf temperature.
Keep learning
Pair this calculator with our pH & EC guide, crop targets in plant guides, and meter picks in product reviews.