Light Distance Calculator
Enter a known PPFD measurement from your grow light’s manufacturer chart, then estimate the PPFD and DLI at a different distance.
To use this calculator, find a PPFD number from your grow light’s chart. Enter that PPFD, the distance where it was measured, and the new hanging height you want to test.
The calculator estimates your new PPFD and your Daily Light Integral, or DLI, based on how many hours per day your light is on.
Estimate Light at a New Distance
Start with a PPFD value from your light’s chart. Then enter the original chart distance, your new hanging distance, and how many hours per day the light runs.
Example: 600 PPFD at 12 inches from the manufacturer’s chart.
The distance listed on the chart for that PPFD value.
The height you want to test.
Use the same unit for chart distance and new hanging distance.
Example: 14, 16, or 18 hours per day.
DLI = PPFD × Hours × 3600 ÷ 1,000,000
Your Estimated Results
These numbers estimate how much light reaches your plant canopy at the new hanging distance.
Moderate Light
This range can work well for many herbs, microgreens, leafy greens, and vegetative growth. Watch plant response and adjust as needed.
| Plant / Growth Stage | Suggested PPFD Range | Suggested DLI Range | General Notes |
|---|---|---|---|
| Seedlings / Clones | 100–250 | 6–12 | Use gentle light. Too much intensity can stress young plants quickly. |
| Microgreens | 150–350 | 8–18 | Crop type, density, and harvest stage matter. Stretching usually means not enough usable light. |
| Leafy Greens | 200–400 | 12–20 | A practical range for lettuce, greens, and many compact edible crops. |
| Herbs | 250–500 | 14–25 | Basil, cilantro, parsley, mint, and similar herbs vary by crop and environment. |
| Fruiting Crops | 500–900+ | 20–35+ | Tomatoes, peppers, and strawberries usually need stronger light and tighter environmental control. |
| Low-Light Houseplants | 50–150 | 2–8 | Not every plant wants full indoor sunshine. Some prefer a calmer light environment. |
How to Use This Calculator
- Find a PPFD value from your grow light’s manufacturer chart.
- Enter the chart distance where that PPFD was measured.
- Enter the new hanging distance you want to test.
- Enter how many hours per day your grow light is on.
- Review the estimated PPFD and DLI.
What Is PPFD?
PPFD stands for Photosynthetic Photon Flux Density. It measures how much plant-usable light reaches a surface every second.
In plain English, PPFD tells you how intense the light is at the plant canopy.
What Is DLI?
DLI stands for Daily Light Integral. It estimates how much total plant-usable light your plants receive in one day.
PPFD is the light intensity right now. DLI is the total amount of light your plant receives over the full day.
Why This Is an Estimate
This calculator uses a simple distance-based estimate. Actual light output can vary based on fixture shape, LED layout, lenses, reflectors, dimming level, tent walls, and whether the plant is directly under the center of the light.
Use this calculator as a starting point. Then watch your plants. Stretching usually means too little light. Bleaching, curling, or dry leaf edges may mean too much light.