Light Bleaching or Heat Stress

Upper canopy leaves appear washed out - pale yellow, cream or white - while lower leaves stay healthy. The lamp is too close or too intense for the current growth stage. Without CO2 enrichment most cannabis cultivars saturate at roughly 800-1000 umol/m2/s; sustained PPFD beyond that mostly creates stress, not extra yield.

What usually causes it

• LED, CMH or HPS mounted too close to the canopy (check the manufacturer minimum distance for the wattage)
• Sustained PPFD above ~900-1000 umol/m2/s without CO2 enrichment
• High canopy temperatures combined with high PPFD pushing VPD out of range

Related product categories

• Climate & Ventilation
• Lighting

Terms worth knowing

• PPFD (Photosynthetic Photon Flux Density)
• DLI (Daily Light Integral)
• VPD (Vapour Pressure Deficit)

Walk the questions if you are not sure this is the match. The notes above are the same ones the tool ends on.