❌ Mistake #1: Light Too Close (Bleaching & Heat Stress)
Symptoms: Top leaves bleached (white/yellow), curling upward, crispy edges, stunted growth directly under light
Cause: Light intensity too high (PPFD above ~1600 µmol/m²/s) or radiant heat from HPS too close
✓ Solution: Raise light 3-6 inches. Measure PPFD at canopy level (aim for 800-1200 PPFD in flower, 400-600 in veg). For HPS, maintain 18-24" distance minimum.
❌ Mistake #2: Light Too Far (Stretching & Low Yield)
Symptoms: Excessive stretch (long internodes), thin stems, slow growth, small buds, plants reaching toward light
Cause: Light intensity too low (PPFD below 400 µmol/m²/s in veg, below 600 in flower)
✓ Solution: Lower light 3-6 inches at a time until PPFD reaches target range. Use PAR meter or phone app to verify. Aim for 800-1000 PPFD in flower, 500-700 in veg.
❌ Mistake #3: Wrong Spectrum for Stage
Symptoms: Excessive stretch in veg (too much red, not enough blue), slow flowering (too much blue, not enough red)
Cause: Using bloom-spectrum lights in veg (heavy red) or veg-spectrum lights in flower (heavy blue)
✓ Solution: Use full-spectrum LED (works for all stages) OR use separate veg lights (metal halide, blue-heavy LED) and flower lights (HPS, red-heavy LED). Most modern LEDs are full-spectrum and work great for both.
❌ Mistake #4: Not Accounting for LED vs HPS Leaf Temp Difference
Symptoms: Slow growth after switching from HPS to LED, nutrient deficiencies appearing, plants look "cold"
Cause: LED produces less radiant heat → Leaf temps are 5-8°F COOLER than under HPS → Lower VPD → Reduced transpiration → Slower nutrient uptake
✓ Solution: When switching to LED, raise ambient temperature by 3-5°F and/or lower humidity slightly to increase VPD. Use our VPD calculator (link in menu) to target leaf temp, not just air temp.
❌ Mistake #5: Ignoring DLI (Running Lights Too Dim for Too Long)
Symptoms: Slow growth despite "long" light hours, plants look healthy but just... slow
Cause: Low PPFD + long hours = Low DLI. Example: 400 PPFD for 18 hours = only 25.9 DLI (barely minimum for veg)
✓ Solution: Calculate your DLI (use our calculator above). Target 30-35 DLI in veg, 40-50 DLI in flower. It's better to run 800 PPFD for 12 hours (34.6 DLI) than 400 PPFD for 18 hours (25.9 DLI).
❌ Mistake #6: Not Adjusting Light Height as Plants Grow
Symptoms: PPFD starts perfect, but 2 weeks later plants are bleached (light got too close as plants grew into it)
Cause: Set-it-and-forget-it mentality — plants grow UP, light distance shrinks, PPFD increases
✓ Solution: Check canopy distance weekly. Measure PPFD at top of canopy every 1-2 weeks during flower (growth is fastest). Adjust height to maintain target PPFD. Consider using light hangers with ratchets for easy adjustment.
❌ Mistake #7: Buying Cheap "Amazon Special" LEDs (False Wattage Claims)
Symptoms: "1000W" LED draws only 100W from wall, plants stretch and yield poorly, light burns out after 6 months
Cause: Cheap LEDs use "equivalent wattage" marketing (comparing to HPS) instead of actual power draw. Often use low-quality diodes (Epistar instead of Samsung/Osram).
✓ Solution: Buy from reputable brands (Gavita, HLG, Growers Choice, AC Infinity, Fluence). Check ACTUAL power draw (e.g., "240W from wall"). Look for Samsung LM301 diodes. Expect to pay $1-2 per watt for quality LED.
