Light burn on cannabis shows up as yellowing or white bleaching on the leaves and buds closest to your grow light. Unlike nutrient problems that typically start at the bottom of the plant, light burn hits the top of the canopy first, right where light intensity is strongest. The affected leaves stay firm and attached to the plant, which is one of the easiest ways to tell it apart from other issues.
What Light Burn Looks Like
The earliest sign is a pale yellowing on the upper leaves, specifically the ones sitting directly under your light fixture. As the damage progresses, leaf tissue turns pale while the veins stay green, a pattern called interveinal yellowing. This creates a striped or mottled look that’s distinct from the uniform yellow of a nitrogen deficiency.
If the light stays too close or too intense, that yellowing eventually shifts to white. The leaves become dry, crispy, and papery to the touch, sometimes developing brown flecks across their surface. On buds, the damage is even more dramatic: the calyces bleach to a stark, lifeless white. These “albino” buds might look unusual or even appealing at first glance, but they’ve lost most or all of their cannabinoid content and often have no recognizable cannabis smell. Vertical growth at the affected tops tends to stall out, with tight, compressed spacing between nodes.
Light Burn vs. Heat Stress
Because grow lights produce both light and heat, these two problems often get confused. They can also happen simultaneously. But they look different if you know what to check.
Light burn creates uniform bleaching concentrated at the very top of the canopy, wherever photons hit hardest. Heat stress, on the other hand, causes the leaf edges to curl aggressively upward into a shape growers call “tacoing.” With heat stress, you’ll also see scorching on the serrated tips and edges of the leaves rather than the even, top-down yellowing of light burn. The whole plant may look wilted and limp even when the growing medium is moist, and the canopy will feel noticeably warm to the back of your hand.
A quick way to tell them apart: light-burned tissue is dry, crispy, and bleached. Heat-stressed tissue is wilted, limp, and burnt around the edges.
Light Burn vs. Nutrient Deficiency
Nitrogen deficiency also turns leaves yellow, which is why growers frequently misdiagnose light burn. The key difference is location. Nitrogen deficiency starts at the bottom of the plant on the oldest leaves and works its way up. Those leaves soften and eventually fall off. Light-burned leaves stay at the top, remain firm, and don’t drop.
Nutrient burn from overfeeding is another common lookalike. It typically shows as brown, crispy tips on leaves throughout the plant, often accompanied by overly dark green foliage and pronounced veins. Light burn doesn’t darken leaves; it does the opposite, stripping color away. If you’re seeing yellowing only on the uppermost growth and your feeding schedule hasn’t changed, light intensity is the more likely culprit.
How It Affects Potency
Light-bleached buds aren’t just a cosmetic problem. The same process that strips the green from the tissue also degrades the active compounds inside. Bleached buds tend to have low potency or, in severe cases, no measurable cannabinoid content at all. The terpenes responsible for aroma break down as well, leaving flower that smells flat or like hay. Even partially bleached buds from the top cola will test noticeably weaker than healthy buds from lower on the same plant.
Why It Happens
Cannabis thrives under intense light compared to most plants, tolerating 950 to 1,200 PPFD (a measure of light intensity) during flowering, which translates to a daily light integral of roughly 41 to 51. But every plant has a ceiling. Once light intensity exceeds what the plant can use for photosynthesis, the excess energy destroys chlorophyll, the pigment responsible for green color and light absorption.
Inadequate CO2 is often the real bottleneck. In a sealed grow room without CO2 supplementation, plants max out their ability to use light much sooner. Turning up your light without also increasing CO2 is one of the fastest ways to trigger light burn. The plant simply can’t process all the photons it’s receiving, and the surplus causes damage.
How to Fix It
The first step is increasing the distance between your light and the canopy. During flowering, most LED manufacturers recommend 18 to 24 inches between the fixture and the tops. For high-powered lights (1,000 watts or more), 24 to 36 inches is a safer starting point, especially if you’re already seeing symptoms. If your light has a dimmer, reducing intensity by 10 to 20 percent is often easier than physically raising the fixture.
Supercropping or bending the tallest colas away from the light can also help when raising the fixture isn’t possible. Some growers use a screen or trellis to keep the canopy flat so no single top gets significantly closer to the light than the rest.
Can Damaged Leaves Recover?
Leaves that have fully bleached to white will not regain their green color. The chlorophyll in that tissue is gone. However, the plant itself can recover if you correct the light distance before the damage spreads. New growth should come in healthy, and leaves that were only mildly yellowed may stabilize, though they won’t return to their original shade. Buds that have already bleached are a loss in terms of potency, so catching light burn early, when you first notice pale upper leaves, makes a significant difference in final harvest quality.