Your grow light too close seedlings shows itself through several clear warning signs. Watch for leaves that curl upward, turn pale yellow, or develop white bleached patches. Brown crispy edges on the leaves closest to the fixture tell you damage has started. These signs of light stress plants give you mean you need to act fast before things get worse.
I learned to spot these symptoms after burning a tray of lettuce seedlings last spring. My LED panel hung just 3 inches above the soil. The plants looked fine for the first few days. Then the edges of the top leaves started turning brown and papery. Within a week, half the tray had crispy, dead growth that never recovered.
Here's what happens inside the leaf when lights sit too close. Plants can only use so much light at once. Extra photons create energy the plant can't process. This damages the chlorophyll that makes leaves green. You see the damage as yellow or white patches where pigment has broken down. Iowa State Extension notes that bleached or brown leaf tips mean your light needs to move up.
The seedling light burn symptoms follow a pattern you can track. First, leaves curl upward trying to reduce their exposure to the light. Next, the color fades from bright green to pale yellow, starting at the top of the plant. Then white bleached spots appear on the parts closest to the fixture. The final stage brings brown crispy edges as tissue dies. Catching it early makes fixing the problem much easier.
Try the hand test to check if your light is too close. Hold your hand palm-down at the height of your seedling tops. Leave it there for 30 seconds. If the back of your hand feels warm or hot, your seedlings feel it too. LEDs don't give off much heat, but some still produce enough to cause problems at close range.
Check your seedlings every day for early warning signs. Look at the leaves closest to the light first since they show stress before lower ones do. Healthy leaves should stay flat and dark green. Any curling, yellowing, or color change tells you to make adjustments right away.
The fix takes just a minute. Raise your light 4 to 6 inches higher than where it hangs now. If you can't raise it, reduce run time from 16 to 12 hours per day. Some fixtures have dimmer controls that let you turn down the power. Any of these changes cuts the light stress on your plants.
Not all seedlings respond the same way to light. Tomatoes and peppers tolerate closer lights than lettuce or herbs. Young seedlings with only their first leaves are most fragile. As plants grow bigger and stronger, you can move lights closer without causing damage. Start high and lower your fixture over time as plants mature.
Read the full article: Best Grow Lights for Seedlings
