Light Level & Lux Guide
Enter a light-meter reading and how long it lasts each day to estimate the Daily Light Integral of a garden spot, and see which shade category it falls into.
Light level
Why light level matters more than "shade"
Gardeners talk about "shade" as if it were one thing, but a bed under a high oak canopy, a spot on the north side of a house, and the deep gap between two garages all get very different amounts of light — and a plant that thrives in one can sulk or stretch leggily in another. A numeric estimate, even a rough one, is far more useful than guessing from the label "shady."
Daily Light Integral is the metric growers actually use because it accounts for both brightness and how long that brightness lasts. A dim spot lit for ten hours can deliver about as much total light as a brighter spot lit for three, and DLI is what lets you compare the two on equal footing.
Frequently Asked Questions
What is a Daily Light Integral (DLI)?
DLI is the total amount of usable light a spot receives over a full day, measured in moles of photons per square metre. Two spots can have the same peak brightness at noon but very different DLI if one gets three hours of that light and the other gets eight — DLI captures both intensity and duration in one number.
How does this calculator turn lux into DLI?
It first converts your lux reading into PPFD (the light plants actually use for photosynthesis) using the widely-cited daylight factor of 1 lux ≈ 0.0185 µmol/m²/s, then multiplies that by the number of seconds in your stated daylight window and divides by a million to get moles per day. It's an estimate — the exact factor shifts a little with cloud cover and the light's spectrum.
How do the shade categories map to DLI?
As a rough field guide: full sun sits above 20 mol/m²/day, light shade or partial sun runs 10–20, partial shade 4–10, full shade 1.5–4, and deep shade is under 1.5. Most classic shade perennials — hostas, ferns, astilbe — thrive in the full-shade to partial-shade range.
Where should I take the reading?
Hold the meter (or phone light-meter app) at the height your plants will actually sit, on a typical clear day, at the time of day the bed gets its best light. Take a few readings across the season if you can — deciduous tree canopy changes a bed from full sun in early spring to deep shade by midsummer.
Educational tool only. Results are estimates using a standard daylight conversion factor — real spectra and cloud cover shift the true value. Use it to compare beds relatively, not as a lab-grade measurement.