Fiddle Leaf Fig & Houseplant Light Guide

What is DLI?

DLI means Daily Light Integral. It is the total photosynthetically useful light that hits a leaf in 24 hours, measured in moles of photons per square meter per day (mol·m⁻²·d⁻¹). You will also see it written as mol/m²/day.

A south window at 2 p.m. can look violent and still deliver a mediocre day if a building cuts the morning and a sheer cuts the afternoon. A bright-east room that is open from 7 a.m. can win. That is the point of DLI. Brightness × duration.

This calculator is a model from window direction, distance, glass, and hours you type in. It is not a quantum sensor. A cheap meter will beat it. Use the estimate to compare two placements in the same apartment, not to argue with a lab.

DLI vs foot-candles

Foot-candles (fc) answer: how bright is it right now, on this spot. One foot-candle is the light of one lumen on one square foot. Phone apps that say “lux” are the metric cousin (roughly 10 lux ≈ 1 fc).

DLI answers: how much of that light did the plant bank today. Two rooms with the same noon foot-candle reading can have very different DLIs if one is shaded by 3 p.m.

Indoor foliage plants are not greenhouse tomatoes. They do not need field-crop DLI. They do need enough integral that internodes stay short and variegation does not collapse to green.

What DLI do houseplants want?

These are typical indoor targets, not prescriptions. Species, season, and your meter will disagree. The calculator’s “ideal” band is in this neighborhood:

• Low-light survivors (ZZ, snake plant, some pothos in a hall): often fine in a low indoor DLI, roughly the 1–4 range.
• Most foliage aroids (pothos, philodendron, monstera): happier in the middle indoor band, roughly 4–10.
• Fiddle-leaf fig (Ficus lyrata), citrus, and other “I wanted a tree” plants: they want the high end of what a house can give, often talked about in the 8–12+ range if you can get it without cooking the leaf.

If the tool returns a DLI under about 3 for a fiddle-leaf or a variegated Marble Queen, believe the direction: that corner is why the internodes stretched. Move it or add a lamp. Then re-run the page with the new distance.

Palma’s live plants live on the Houseplant Guide. A fiddle-leaf is on this URL because people search it. If we do not have one in stock, the light math is still the same.

Why a south window is not automatically enough

Direction is only one input.

• Distance: Intensity falls off fast. Three feet back is a different plant than on the glass.
• Glass and sheers: Dirty glass, film, and curtains cut both foot-candles and DLI.
• Hours: A west window that is only clear from 3–5 p.m. can scorch and still lose the day to an east room that works all morning.
• Obstructions: Overhangs, other buildings, trees in leaf. Winter can raise DLI in a deciduous street and drop it in summer.

Run two setups: the spot you have, and the spot you are considering. The useful output is the gap between them.

Can I use a phone light-meter app?

Yes, as a relative tool. Phone sensors were not built as horticultural meters. They drift, they hate pointed sun, and they do not integrate a day unless you stand there taking readings. If you use one: measure at leaf height, same time of day, same orientation, write the number down, compare next week. Then convert the day’s pattern in your head toward DLI, or keep using this page for the integral estimate.

Light and watering are the same problem

More DLI means the mix dries faster. Less DLI means Sunday watering becomes rot. After you pick a window, size the pour with the watering calculator and still use the finger test. Yellow leaves after a move: yellow-leaf tool.