Light is the most important starting point for healthy plant growth: it powers photosynthesis and the production of leaves, roots and flowers. Too little causes weak growth and in worst case starving it to death; too much can scorch it and kill too. A plant's right light range depends on its origin: a rainforest-understory species and a plant from an exposed desert evolved for very different daily light. Usable light changes just as dramatically with latitude, season, window direction and distance from the glass. In winter, a north-facing window in Austin receives more light than a south-facing window in Stockholm. We use real light values for any location on Earth. Plantlight finally answers every grower's eternal question: Where should I put this plant?
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Step 3
Tune the selected lamp or use your own
When extra light is recommended, the planner aims for the lower ideal DLI. Every change below updates the monthly line and hours on the graph.
Choose a SANSI lamp above, or switch to your own lamp.
Lamp values
PPFD and power draw come from the selected SANSI lamp. Choose My own lamp to edit them.
12.0 in
Estimated PPFD at the canopy: — µmol·m⁻²·s⁻¹
EUR
Peak light time—hours/day in the darkest monthAnnual energy—kWh/yearEstimated annual cost—at your electricity price
Suggested daily timing
When to run the lamp
Target DLI is automatically set to
mol·m⁻²·day⁻¹,
the current recommended DLI target for the selected plant.
Suggested extra lightSelect a lamp to calculate timing
Sunrise and sunset will appear after a location is selected.
Timing will use the calculated lamp hours, local sun path and growing-space conditions.
Export a schedule for an automatic timer or smart switchAn automatic switcher is a smart plug, relay or home-automation system that turns the lamp on and off at saved times. Exporting avoids resetting a timer by hand as daylight changes through the year.
Monthly is the simplest setup. Weekly follows seasonal daylight changes more closely. Daily is the most precise and creates the largest schedule.
Home Assistant is smart-home software; this YAML can automate a compatible smart plug or relay.
Automatically selected from the growing location.
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Plant sellers tools
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Use Plantlight to help customers place their plants, earn from relevant grow-light recommendations and show plants you have available.
1
Create a QR code or customer link
Help customers quickly find the right light for each plant in their home or garden. Use the link on planters, labels or your website or blog, branded with your company name and logo.
Labels such as low light, bright indirect and full sun mean different things in different places. Our model turns a real location and growing position into monthly DLI, then compares it with an evidence-based biological light range for the plant.
01
Start with the light at your location
We begin with modeled open-sky solar DLI near the selected coordinates. DLI is the plant's daily light budget: it totals the photosynthetically active photons received over a complete day. We use all twelve months and local day length, not one annual average.
DLI = PPFD × hours × 3,600 ÷ 1,000,000
02
Translate open sky into a real growing place
Open-sky DLI is adjusted for the selected position. Outdoors, that means full sun, part sun, filtered light or shade. Indoors, the model accounts for hemisphere-aware window direction, distance from the glass, glazing and obstruction. A measured PPFD or lux value, or a grow light's delivered PPFD and hours, can replace or supplement the estimate.
03
Build a biological light profile for each plant
We combine natural habitat and origin, published DLI or PPFD trials when available, greenhouse and horticultural evidence, light descriptions such as full sun or partial shade, and structured light indexes. That evidence is normalized into survival, acceptable and sustained-growth minimums, an ideal range, a high-light stress point and a damage-risk point.
04
Calibrate the classes against real evidence
Numeric light trials and real growing observations provide calibration anchors. Native-location DLI and habitat help distinguish desert-strength full sun from open exposure at a cool, high-latitude site. When stronger species evidence disagrees with a broad class or genus rule, the species is reviewed and corrected.
05
Compare the plant and position month by month
The calculator compares received DLI with the plant's thresholds for every month. It can rank concrete outdoor exposures and window placements, show when light is suitable, identify months that need supplemental light and warn when shade may be useful. Frost and USDA hardiness remain separate so good light is never mistaken for safe outdoor temperature.
06
Keep confidence and limits visible
Every plant profile retains its evidence sources and confidence. A measured value is stronger than a description converted by the model, and reviewed species evidence is stronger than a genus fallback. Buildings, unusual glass, curtains and room geometry can still change the result, so a leaf-level light reading is the best final check when precision matters.
Evidence and interpretation
What the calculator uses—and what it cannot know
Location values represent modeled open-sky solar DLI near the coordinates. Indoor estimates apply transparent position factors; buildings, glazing, trees and room geometry can make the real value different. A plant-level PPFD reading remains useful for checking the modeled result, while the scheduling block intentionally follows the selected location and position.
Plant ranges come from our evidence database and retain source and confidence details. DLI targets describe useful biological ranges, not a promise of growth: temperature, water, nutrition, humidity, acclimation, photoperiod and plant health still matter.
It can be useful for comparisons, but phones vary. Lux is weighted for human vision, while plants use photosynthetically active radiation. This calculator schedules from the location and selected position; use a quantum sensor if you want to validate the modeled PPFD at the leaves.
Should I run the grow light for all calculated hours at night?
Usually no. The scheduler places lamp time in dimmer morning or evening shoulders, biases timing away from the strongest window light, or uses a solar-noon-centred block when the lamp is the main light source. It keeps a consistent dark period and does not replace species-specific flowering control.
Why does my plant still struggle when DLI looks sufficient?
Too much root moisture, temperature stress, pests, low humidity, nutrient imbalance, poor acclimation or excessive leaf temperature can resemble a light problem. Treat DLI as one part of the diagnosis.