Light is what turns pale, stretched seedlings into compact, deep-green microgreens. The good news is that microgreens need far less light than tomatoes or peppers, because they are harvested within two weeks. For most home growers, an inexpensive LED shop light does the job perfectly.
The short version
- Hours: 12–16 hours of light a day, on a timer.
- Distance: LED shop lights about 3–6 inches above the seedlings; stronger LED panels further away, per the maker’s guidance.
- Intensity: roughly 100–250 µmol/m²/s PPFD at the canopy is plenty.
- Color: “daylight” white (5000–6500K) or full-spectrum white works well.
Do microgreens need a grow light?
Not always. A bright, south-facing window (north-facing in the Southern Hemisphere) can grow good microgreens in spring and summer. But window light has two problems:
- It’s one-sided, so seedlings lean hard towards the glass and can fall over.
- It’s weak in winter and on cloudy days, giving pale, stretched trays.
If your microgreens are leggy, yellow or leaning, a light is the most effective upgrade you can make. See why microgreens fall over and why they turn yellow.
How many hours of light per day?
Give microgreens 12–16 hours of light a day, starting the day you remove the blackout cover. 16 hours on and 8 hours off is a common schedule. Use a cheap plug-in timer so it’s consistent.
Some growers run lights 18–24 hours to speed growth, but the gains are small and electricity use goes up. A dark period also gives you a chance to spot problems.
How close should the light be?
It depends on how strong the light is.
| Light type | Typical distance above seedlings |
|---|---|
| LED shop light / T5-style LED tube (20–40 W) | 3–6 inches (8–15 cm) |
| Compact LED panel or bar (50–100 W) | 8–18 inches (20–45 cm), per manufacturer |
| Larger LED grow panel (100 W+) | Follow manufacturer’s recommendation for seedlings |
| Standard household LED bulb | 4–8 inches; covers only a small tray |
Signs the light is too far: stretched, pale, leaning seedlings. Signs it’s too close or too strong: leaf edges bleaching white or yellow, curling, or the canopy feeling warm to the touch. LEDs produce little heat, but very strong panels can still stress tiny seedlings.
A little light science: PPFD and DLI
If you want to go beyond “a few inches”, two measurements help:
- PPFD (photosynthetic photon flux density) is how much usable light reaches the plants each second, measured in µmol/m²/s.
- DLI (daily light integral) is the total usable light over a day, in mol/m²/day.
A common target range for microgreens is a PPFD of about 100–250 µmol/m²/s, which over a 16-hour day gives a DLI of roughly 6–14 mol/m²/day.
DLI = PPFD × hours of light × 0.0036
Example: 150 µmol/m²/s × 16 hours × 0.0036 = about 8.6 mol/m²/day
You can measure PPFD with a quantum meter. Some phone apps estimate it, though they’re much less accurate. Most growers simply use a shop light at the right distance and judge by how the plants look.
What kind of light to buy
LED shop lights (best value)
Linkable 2–4 ft LED shop lights or T5-style LED tubes are the classic microgreen light. One 4 ft light covers about two 10×20 trays side by side when hung close. They’re cheap, cool-running and easy to hang from shelves with chains or hooks. Look for:
- Around 4000–6500K color temperature (“cool white” or “daylight”).
- A high lumen output for the wattage.
- Linkable units if you’ll add more lights later.
LED grow bars and panels
Purpose-built grow lights are more powerful and often more efficient. They make sense for multi-shelf setups or slow crops, but they’re overkill for one or two trays.
Purple (“blurple”) lights
Red-and-blue LED lights work, but the purple glow makes it hard to judge plant color and health, and it’s unpleasant in a living space. White full-spectrum lights are easier to live with.
What does it cost to run?
A 36-watt LED shop light running 16 hours a day uses about 0.58 kWh per day, or around 17 kWh per month. Multiply by your electricity rate per kWh to get your monthly cost. For most households, that’s a small cost for a steady supply of fresh greens.
Setting up a simple light
- Hang the light above the tray using adjustable chains or ratchet hangers so you can raise it as plants grow.
- Start with the light about 4 inches above the seedlings (for a shop light).
- Plug it into a timer set for 16 hours on, 8 off.
- Check after two days: adjust closer if seedlings stretch, or higher if leaves bleach.
For building a full shelf, see how to set up a microgreens shelf in a small space.
Frequently asked questions
Can I use a regular LED bulb for microgreens?
Yes, for a small tray, if it’s close (4–8 inches) and bright. A shop light spreads light more evenly over a full tray.
Do microgreens need light during blackout?
No. Keep them covered and dark for the first 3–4 days, then switch on the light. See the blackout period.
Can microgreens get too much light?
Yes. Very strong light very close can bleach and curl leaves. With ordinary shop lights this is rare.
Should I leave the light on 24 hours?
It isn’t necessary. 12–16 hours is enough for good growth and saves electricity.
