Recognising and avoiding light burn: Cannabis light damage

Light burn is one of the most common types of damage caused by intensive LED lighting:

**What is light burn?

Lightburn occurs when cannabis receives more light than it can process. The photosynthesis capacity is exceeded and cell damage occurs.

**Distinguish lightburn vs. other damage:**

*Lightburn symptoms:*

- Bleaching (white-yellow discolouration) of the uppermost leaves

- Starts directly under the lamp

- Only affects areas close to the light

- Leaf veins remain green, spaces between leaves turn white

- Leaves feel dry and brittle

*Not to be confused with:*

- Nutrient deficiency: Affects the whole plant, not just the light area

- Heat damage: leaves curl upwards

- Nutrient burn: Brown leaf tips, starting on older leaves

**Light burn stages:**

*Stage 1 - early detection:*

- Slight yellowing of the leaf tips

- Only uppermost leaves affected

- Still reversible due to immediate adaptation

*Stage 2 - Advanced:*

- Distinct white-yellow spots

- Several leaf layers affected

- Growth slows down

*Stage 3 - Severe:*

- Complete bleaching of entire leaves

- Leaves turn brown and die

- Loss of yield unavoidable

**Immediate measures for light burn:**

*Reduce light intensity:*

1. Hang the lamp higher (5-10cm steps)

2. Reduce dimmer to 70-80%

3. Shorten lighting time (for autoflowers)

*Affected leaves:*

- Leave slightly affected leaves on

- Remove severely damaged leaves

- New leaves should grow back healthy

*Optimise the environment:*

- Lower the temperature (below 26°C)

- Increase humidity (40-60%)

- Improve CO2 supply

**Light burn prevention:**

*Maintain the correct distances:*

- LED panels: 30-60cm minimum distance

- COB-LEDs: 45-75cm distance

- HPS: 60-100cm distance

- Observe manufacturer's specifications, but start conservatively

*PPFD measurements:*

- Measure regularly with a par metre

- Identify and defuse hotspots

- Aim for uniform light distribution

*Gradual familiarisation:*

- Increase light intensity slowly

- Start at 50% output

- Increase by 10-20% weekly

- Observe plant reaction

**Variety-specific tolerance:**

*High light tolerance:*

- Sativa-dominant hybrids

- Equatorial landraces

- Modern high-THC varieties

*Low light tolerance:*

- Indica-dominant strains

- CBD-rich strains

- Autoflower (especially early)

**Measuring devices and monitoring:**

*PPFD limits:*

- Seedlings: Max 300 PPFD

- Vegetative: Max 600 PPFD

- Flowering: Max 1000 PPFD (with CO2)

- Without CO2: Max 800 PPFD

*Continuous monitoring:*

- Daily visual inspection of the leaves

- Weekly PPFD measurement

- Photos for progress documentation

**Recovery after light burn:**

*Short term (1-2 weeks):*

- Maintain reduced light intensity

- Do not additionally stress stressed plants

- No training or pruning

*Long term (3-4 weeks):*

- Slowly increase light when new leaves are healthy

- Maintain optimal environmental conditions

- Gain experience for next grow

**Frequent light burn