There is no single correct distance. How far to hang an LED grow light from your plants depends on the light's power, how it spreads its light and how bright you set it. Most LED fixtures hang somewhere between about 12 and 24 inches above the plants, but the right answer is the height that gives your crop the intensity it needs without scorching it.
Why distance matters
The intensity of light that reaches a leaf falls as you move the light away. Hang the light too close and the leaves closest to it receive more light than they can use, which can bleach or scorch them. Hang it too far and the plants stretch toward the light, growing tall, pale and weak. Distance is simply the easiest way to set the intensity.
What decides the right height
- Power. A stronger light needs to be higher than a weaker one to deliver the same intensity.
- Optics and layout. Lights with lenses concentrate light and need more height than a flat panel that spreads it.
- Dimmer setting. Turning a light down is the same as moving it away. A dimmer lets you change intensity without moving the fixture.
- Crop and stage. Seedlings want gentler light than fruiting plants. See what PPFD is for typical targets.
- Light type. Fluorescent lights go within a few inches of plants, which is why older advice says 4 to 8 inches. LED fixtures are usually higher.
Typical starting heights
Extension services written for fluorescent seed-starting lights advise keeping them about 4 to 8 inches above seedlings: North Dakota State University says no more than 4 to 6 inches, and Oklahoma State University suggests 6 to 8. LED fixtures are generally hung higher, commonly 12 to 24 inches depending on wattage and lens design, because they are brighter per fixture.
| Situation | Starting point |
|---|---|
| Fluorescent lights over seedlings | About 4 to 8 inches |
| Low-power LED strip or bar | Close, often 6 to 12 inches; follow the maker |
| Full-size LED panel for a tent | Often 12 to 24 inches, depending on wattage and dimming |
| Any light | The maker's PPFD chart at your chosen setting |
These are only starting points. The best source is the manufacturer's PPFD map for your light, which shows the intensity at several heights. Always start higher or dimmer than you think you need, and move closer in small steps.
How to set the height step by step
- Pick your target intensity for the crop and stage, for example about 200 µmol/m²/s for seedlings and leafy greens or 600 or more for fruiting plants.
- Look up the light's PPFD map to see which height gives that intensity at your dimmer setting.
- Hang the light a little above that height and check the plants after a day or two.
- Lower the light or raise the dimmer in small steps if plants look pale or stretched.
- Measure if you can. A quantum sensor reads the real intensity at leaf level.
Signs the light is too close
- Leaves that bleach to white or pale yellow near the light
- Leaf edges that curl upward or look scorched
- Leaves that droop at midday though the soil or water is fine
- Slow, stunted growth in the top of the plant
The fix is to raise the light or dim it.
Signs the light is too far
- Tall, thin, leggy stems with large gaps between leaves
- Seedlings that lean toward the light
- Pale green leaves and weak growth
- Slow growth overall
The fix is to lower the light, raise the dimmer or lengthen the day. Read daily light integral explained.
The hand test and its limits
Some growers hold the back of a hand at plant height for about 30 seconds. If it feels uncomfortably warm, the plants may be too close. It is a quick check for heat, but it tells you nothing about light intensity, so use it only as a safety check. LED lights run cooler at the plant than HID lights, so heat alone is a poor guide. Read LED vs HID grow lights.
Keep the canopy even
- Rotate pots so that each plant gets its turn in the brightest spot.
- Raise the light as plants grow so the distance to the top leaves stays about the same.
- Group plants of similar height together.
- Use adjustable hangers so you can change the height in seconds. See grow tent lighting setup.
Seedlings and young plants
Young plants are the easiest to burn and the quickest to stretch. Start with the light high or dimmed, move closer as the first true leaves appear and raise it as the plants grow. See starting seeds indoors with LED grow lights.
How light spreads from a panel
A small, bright source, such as a bare bulb, loses intensity quickly as you move away. A large, flat panel behaves differently: close to the panel the light is fairly even and falls off slowly, but far from it the panel looks like a single source and intensity falls faster. That is why height matters more for a small light than for a large panel, and why a PPFD map is specific to one light at one height.
- Closer gives more intensity but a smaller, less even footprint.
- Higher gives less intensity but a wider, more even footprint.
Height by setup
| Setup | What to do |
|---|---|
| A shelf for seedlings and greens | Mount the light on the shelf above, with a way to raise it; dim for seedlings |
| A grow tent | Hang from the frame with adjustable hangers; keep the canopy even |
| A room with tall plants such as a citrus tree | Hang above and angle the light to reach the sides; rotate the pot |
| Over hydroponic jars | Mount above the leaves, not the water, and keep the reservoir covered |
Plant height and training
The plants are not all the same height, and the tallest get the most light. You can level a canopy by:
- Pruning tall shoots so the top is even.
- Grouping plants of similar height.
- Bending or tying down tall branches on fruiting plants.
- Raising short plants on a box or a stand.
A quick troubleshooting guide
| Symptom | What to try first |
|---|---|
| Stretching | Lower the light or raise the dimmer |
| Bleaching at the top | Raise the light or dim it |
| Uneven growth | Rotate pots; level the canopy; check the light's edges |
| Hot leaves | Check airflow and raise the light a little |
Key takeaways
- There is no single distance; it depends on power, optics and the dimmer setting.
- LED fixtures usually hang higher than fluorescent lights, commonly about 12 to 24 inches, but follow the maker's PPFD chart.
- Stretching means too far or too weak; bleaching or curling means too close or too strong.
- Start high or dimmed and move in small steps.
- Raise the light as plants grow, and keep the canopy even.
Use the dimmer instead of moving the light
Because intensity depends on both height and brightness, the easiest way to change it is the dimmer. My LED Grow Lights have a dimmer switch that gives you full control of the light intensity, so you can dim for seedlings and raise it for fruiting without rehanging the fixture. See all of our LED grow lights, or go back to growing with LED lights.
Related reading
- Grow Tent Lighting Setup
- Starting Seeds Indoors With LED Grow Lights
- Back to Growing With LED Lights