How Much Light Do Indoor Plants Need?
By Desmond Hale · September 25, 2026 · 8 min read
Quick answer
Leafy greens and most herbs need 4–6 hours of direct sun or 12–14 hours under an LED. Fruiting crops like tomatoes need 8+ hours of strong light. Foliage houseplants manage on bright indirect light alone.
Indoors, light intensity drops off far faster than people expect: a spot three feet back from a window can receive less than a quarter of the light available at the glass. That gap explains most disappointing indoor gardens.
What your window direction gives you
| Window | Light available | Good for |
|---|---|---|
| South | 6–8 hrs direct | Tomatoes, peppers, basil, rosemary |
| West | 4–6 hrs direct, warm | Herbs, kale, chard |
| East | 3–5 hrs gentle direct | Lettuce, spinach, parsley, mint |
| North | Bright indirect only | Green onions, foliage plants, microgreens |
Hours matter as much as intensity
Plants accumulate light over the day. A moderately bright grow light running 14 hours can out-produce a brief burst of intense afternoon sun. This is why an inexpensive LED on a timer is so effective — it extends duration, which windows cannot.
How to tell a plant needs more light
- Stems stretch with long gaps between leaves (etiolation).
- New leaves are smaller and paler than old ones.
- The whole plant leans hard toward the window.
- Herbs taste weak; fruiting plants flower but drop blossoms.
Positioning plants and lamps
Keep pots within a foot of the glass where possible, and rotate a quarter turn weekly so growth stays even. Under an LED bar, keep leaves 6–12 inches below the fixture — close enough to be useful, far enough to avoid heat stress.
Seasonal adjustments
Winter sun is weaker and shorter. Expect to add 2–4 hours of lamp time from late autumn, and move light-hungry plants to your best window for the season.
Frequently asked questions
Is a regular LED bulb enough for plants?
A bright white LED can keep foliage plants alive, but it lacks the intensity for vegetables. A purpose-made full-spectrum grow light costs little more and delivers several times the usable light.
Can plants get light through a window at night from streetlights?
Streetlight levels are far too low to matter for growth, though very bright light at night can disrupt flowering in a few sensitive species.
How many hours should I run a grow light?
12–14 hours a day for leafy greens and herbs, 14–16 for fruiting crops. Always give plants a dark period; continuous light stresses most species.
