How Much Light Do Houseplants Need in Winter?
Three to ten moles a day for most of them — and the useful question is how far short your window falls.
By Scooter M. — An enthusiast who's genuinely into this. I read the manuals, compile the published specs, and do the math. No lab coat.
Published · How we pick
Photographs on this site are licensed stock and are illustrative of the fixture type. We do not own the units we write about.
How this page is funded: the buy links here are Amazon Associates links, and we earn a commission on qualifying purchases at no extra cost to you. We have not been paid to feature anything on this page, we accept no free product, and commission plays no part in the ranking. Full disclosure.
We have not tested these units. Everything below comes from the manufacturer’s own published specifications, or from arithmetic we have shown our working for. Where a figure is not published, we say so instead of estimating one. Read the method.
Quick picks
Efficacy is photons out per joule in. Where a manufacturer publishes it we quote theirs; where they publish photon output and wattage but not efficacy, we divide and label it as ours; where they publish neither, the cell says so rather than guessing. Tap a row for the full write-up.
| # | Product | Best for | Efficacy | Price |
|---|---|---|---|---|
| 1 |  SANSI 36W BR30 Grow Light Bulb The rare grow bulb that publishes both PPF and a PPFD figure with the measurement distance attached, which is the only reason it can be sized honestly. | Topping up one plant | 1.82 umol/J (ours) | |
| 2 |  AC Infinity IONBOARD S22 The highest published efficacy of any fixture here at 2.7 umol/J, on Samsung LM301H diodes, with dimming in real 20% steps rather than a vague knob. | A whole shelf | 2.7 umol/J | |
| 3 |  Soltech Aspect Gen 2 The only fixture here you would willingly hang in a living room, and the only one publishing PPFD at three separate distances so it can actually be placed by the numbers. | A room you sit in | 1.39 umol/J (ours) |
The reasoning
Most houseplants want between 3 and 10 moles of light per square meter per day. Iowa State University Extension puts low-light foliage plants at 3 to 6 mol/m²/day, foliage and flowering houseplants at 6 to 10, and flowering houseplants, succulents and leafy herbs at 12 to 16. Those numbers do not change with the season — but what your window supplies does, dramatically.
| Plant category | DLI (mol/m²/day) | Examples |
|---|---|---|
| Low light | 3–6 | Pothos, snake plant, ZZ, most ferns, peace lily |
| Medium light | 6–10 | Monstera, philodendron, calathea, most flowering houseplants |
| High light | 12–16 | Succulents, most cacti, leafy herbs, citrus |
| Very high light | 18–30 | Fruiting crops. Not a windowsill proposition in winter. |
Translating that into intensity
DLI is a daily total, and what you can actually measure or estimate is intensity. University of Minnesota Extension publishes intensity bands for indoor plants that map onto the same categories:
| Category | PPFD | Foot-candles |
|---|---|---|
| Low light | 50–150 µmol/m²/s | 50–250 fc |
| Medium light | 150–250 µmol/m²/s | 250–1,000 fc |
| High light | 250–450 µmol/m²/s | over 1,000 fc |
Target: 4 mol/m²/day, the middle of the low-light band.
At 100 µmol/m²/s for 11 hours: 100 × 11 × 3600 ÷ 1,000,000 = 4.0 mol/m²/day. Met.
At 60 µmol/m²/s for 18 hours: 60 × 18 × 3600 ÷ 1,000,000 = 3.9 mol/m²/day. Also met, with a much dimmer fixture.
Estimating what your window actually gives you
Without a meter you are estimating, and it is worth saying so rather than pretending otherwise. Some useful anchors:
- Full outdoor summer sun is about 2,000 µmol/m²/s (Virginia Cooperative Extension). Everything indoors is a fraction of that.
- Directly in a south-facing window on a clear winter day can be a few hundred µmol/m²/s for a few hours — enough for a medium-light plant if it is genuinely in the window.
- Three feet back from that same window is a small fraction of it. Intensity falls very fast with distance from the glass, in the same inverse-square way it does from a fixture.
- A north window on an overcast January day may supply almost nothing usable. This is the situation supplemental light exists for.
A phone light-meter app measures lux, which is the same unit problem as lumens — weighted to human vision rather than to photosynthesis, so it cannot be converted to PPFD without knowing the spectrum. It is still useful for relative comparisons: measure the windowsill and then measure where the plant actually sits. The ratio is real even though the absolute number is not directly usable.
How the plants report it
| What you see | Likely cause | What to do |
|---|---|---|
| No new growth for two or three months over winter | Below the target DLI. The commonest winter state. | Supplement to 12–16 hours. This is normal and recoverable. |
| New leaves smaller and paler than older ones | Persistently under target | Add light before the plant sheds the older leaves to fund the new ones. |
| Long bare stem between leaves, growth leaning to the window | Well under target — the plant is reaching | Move it closer to the glass and supplement. Prune back in spring. |
| Leaves bleaching or scorching in a bright window | Too much direct sun on a plant adapted to shade | Move it back, or diffuse with a sheer curtain. |
For what to actually buy, see the best grow lights for winter, and for the mechanism behind the seasonal drop, winter daylight loss and what to add.
Every pick in full
SANSI 36W BR30 Grow Light Bulb
Grow bulbTopping up one plant
The rare grow bulb that publishes both PPF and a PPFD figure with the measurement distance attached, which is the only reason it can be sized honestly.
What SANSI publishes
- Power draw
- 36 W (source)
- PPF (photon output)
- 65.6 umol/s (source)
- PPFD
- 265.58 umol/m2/s at 1 ft (source)
- Spectrum
- 4000 K, 400-780 nm, CRI close to 100 (source)
- Rated life
- 25,000 hours (source)
Our arithmetic
- Efficacy, computed from the published figures: 1.82 umol/J
65.6 umol/s / 36 W = 1.82 umol/J. That is roughly a third less efficient than the panels on this page — the price of a screw-in form factor. - Electricity used at 12 hours a day for 30 days: 12.96 kWh a month
36 W x 12 h x 30 d / 1000 = 12.96 kWh.
What SANSI does not publish
- Beam angle
- Fixture dimensions
Who should skip it
Skip it if you are lighting more than one plant. 65.6 umol/s is a small amount of light spread over a cone — it lights a single specimen, not a shelf.
AC Infinity IONBOARD S22
LED panelA whole shelf
The highest published efficacy of any fixture here at 2.7 umol/J, on Samsung LM301H diodes, with dimming in real 20% steps rather than a vague knob.
What AC Infinity publishes
- Power draw
- 115 W (source)
- Efficacy
- 2.7 umol/J (source)
- PPFD
- 1098 PPFD (no measurement distance published) (source)
- Stated coverage
- 2 x 2 ft (source)
- Spectrum
- Samsung LM301H, plus 660 nm, 730 nm, 3000 K, 6500 K (source)
- Diodes
- 272 diodes (source)
- Dimming
- Yes, 0-100% in 20% increments (source)
- Dimensions
- 30.0 x 30.0 cm board, 1.1 cm thick (source)
- Rated life
- 50,000 hours (source)
Our arithmetic
- Photon output implied by the published wattage and efficacy: about 311 umol/s
115 W x 2.7 umol/J = 310.5 umol/s. AC Infinity does not print PPF directly, so this is our arithmetic from two figures it does print.
What AC Infinity does not publish
- PPF in umol/s — only efficacy is given, so photon output has to be derived
- The measurement distance for the 1098 PPFD figure, without which the number cannot be compared to anything
Who should skip it
Skip it if you want to place it by the numbers. AC Infinity prints 1098 PPFD with no measurement distance attached, which makes that figure impossible to use or compare.
Soltech Aspect Gen 2
PendantA room you sit in
The only fixture here you would willingly hang in a living room, and the only one publishing PPFD at three separate distances so it can actually be placed by the numbers.
What Soltech publishes
- Power draw
- 36 W (source)
- PPF (photon output)
- 50 umol/s (source)
- PPFD
- about 50 umol/m2/s at 1 m, 34.9 at 4 ft, 15.5 at 6 ft (source)
- Spectrum
- 3000 K warm white, CRI 98 (source)
- Dimming
- Yes, in-line dimmer 10-100% (source)
- Dimensions
- 3.5 x 3.5 x 6.2 inches (source)
- Rated life
- 50,000 hours (source)
Our arithmetic
- Efficacy, computed from the published figures: 1.39 umol/J
50 umol/s / 36 W = 1.39 umol/J. Roughly half the efficacy of a 2.7 umol/J board — the design premium is paid twice, once at purchase and again every month on the meter.
Who should skip it
Skip it if photons per watt is the metric that matters. At 50 umol/s from 36 W it is the least efficient fixture on this page, and much of the price is industrial design.
Questions people actually ask
+How much light do houseplants need in winter?
+Can I measure light for my houseplants with my phone?
+Why has my houseplant stopped growing in winter?
+How many foot-candles do houseplants need?
Sources
- Iowa State University Extension — Important Considerations for Providing Supplemental Light to Indoor Plants — consulted September 2, 2026
- University of Minnesota Extension — Lighting for indoor plants and starting seeds — consulted September 2, 2026
- Virginia Cooperative Extension — Calculating and Using Daily Light Integral (DLI), SPES-720 — consulted September 2, 2026
Read next
Houseplants
Winter Daylight Loss, and What to Add Back
Why the winter deficit compounds, and how to size the supplement that closes it.
Houseplants
The Best Grow Lights for Winter
Winter is a daily-total problem. Modest fixture, long photoperiod — sized against published targets and costed for the season.
Coverage & Sizing
PPFD Targets by Plant Type
Published light bands mapped to common indoor plants, with the DLI each implies.
Spectrum & PPFD
PAR, PPFD and DLI, Explained
The three photon units, what each measures, and the conversions between them, shown.
Where this sits
This page belongs to Grow Lights for Houseplants and Winter. Every figure on it is either quoted from a named published source or derived in view — the full method is on our methodology page, and how the site is funded is on the affiliate disclosure.