A practical guide to choosing, sizing, and running grow lights for leafy greens, herbs, fruiting crops, and microgreens. Includes PPFD/DLI targets, spectrum tips, example layouts, energy math, troubleshooting, and a quick buyer’s checklist.
AT A GLANCE
• Best overall today: LED bar fixtures (high efficacy, even canopy).
• Aim for PPE ≥ 2.6 µmol/J (great), ≥ 2.9 µmol/J (excellent).
• Control with dimmers + timers; tune to PPFD/DLI, not 100% power.
• Match lights with HVAC/dehumidification to hold target VPD.
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KEY TERMS (FAST)
• PAR: plant-usable light (400–700 nm).
• PPFD: light intensity at canopy (µmol/m²/s).
• DLI: total daily light (mol/m²/day).
• PPF: total output from fixture (µmol/s).
• PPE: fixture efficiency (µmol/J).
• Photoperiod: hours of light per day.
Formula you’ll use: DLI = PPFD × hours × 3600 ÷ 1,000,000
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TARGETS BY CROP/STAGE (START POINTS)
Leafy greens (lettuce, salad mix)
• PPFD: 150–250 in propagation; 250–350 in grow-out
• Photoperiod: 14–18 h
• DLI: 12–17
Herbs (basil, cilantro, parsley)
• PPFD: 250–450
• Photoperiod: 14–18 h
• DLI: 15–25
Microgreens
• PPFD: 150–300 (variety dependent)
• Photoperiod: 12–18 h
• DLI: 8–15
Fruiting crops (tomato, pepper, strawberry)
• PPFD: 500–900 (watch heat/VPD)
• Photoperiod: 12–16 h
• DLI: 20–35
Mushrooms (not plants, but common indoors)
• Use low PPFD for pin/fruit exposure; many species need light cues, not high intensity.
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SPECTRUM (WHAT MATTERS)
• Full-spectrum white + deep red (660 nm) works for most crops.
• Blue (≈450 nm) supports compact growth and leafy quality.
• Far-red (730 nm) can affect morphology/flowering—use judiciously for fruiting crops.
• UV is optional and situational—avoid unless you have a reason and a plan.
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FIXTURE TYPES (PROS/CONS)
• LED bar fixtures: best uniformity, scalable, cool running, easy to clean.
• LED panels/boards: good budget option; watch edge fall-off.
• HPS/CMH (legacy): high heat, lower efficacy; use only if power is cheap and HVAC is sized.
• Strips for racks: ideal for microgreens/seedlings; dense spacing improves uniformity.
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SIZING YOUR LIGHTS (ROOM OR RACK)
Quick approach (greens/herbs):
- Choose target PPFD (e.g., 300 µmol/m²/s for leafy greens).
- Choose photoperiod (e.g., 16 h).
- Check DLI = 300 × 16 × 3600 ÷ 1e6 ≈ 17.3 → in range.
- Use manufacturer PPF (µmol/s) and layout to hit that average across the canopy.
Rules of thumb:
• 4’×4′ (1.2×1.2 m) veg/greens: a 600–700 W quality bar light often covers well at 250–400 PPFD.
• 5’×5′ fruiting: 700–800 W high-efficacy bar light, hung low and dimmed to map PPFD.
• Multi-tier racks: use low-profile bars/strips per shelf to maintain clearance and uniformity.
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HANGING HEIGHTS & DIMMING (START)
• Seedlings: 30–36 in (75–90 cm), 25–40% power
• Veg/greens: 24–30 in, 40–70%
• Flower/fruiting: 12–18 in, 70–100% (adjust to PPFD and plant response)
Always verify with a PAR meter or a reliable PPFD map.
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CONTROL & AUTOMATION
• Timer or app schedule for photoperiod.
• Dimmers to hit PPFD targets and manage heat.
• Group control/daisy-chain for multi-fixture rooms.
• Log height, dim %, PPFD, DLI, temp/RH weekly and adjust.
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ENERGY MATH (COPY THIS)
Monthly kWh = (Total Watts × Hours/day × 30) ÷ 1000
Monthly $ = Monthly kWh × your $/kWh rate
Example: 2 fixtures × 730 W × 16 h × 30 ÷ 1000 = 700.8 kWh
At $0.15/kWh → $105/month (lights only; add HVAC/dehu)
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EXAMPLE LAYOUTS (PLUG-AND-PLAY IDEAS)
4’×8′ tent/room (greens & herbs)
• Two 600–730 W bar fixtures in line, dim to 250–350 PPFD average.
• 16 h photoperiod → DLI ≈ 14–20.
• Add oscillating fans; size dehu to hold RH.
5’×5′ fruiting room
• One 700–800 W high-efficacy bar fixture.
• Target 600–800 PPFD; 12–16 h photoperiod.
• Coordinate with HVAC to manage added transpiration.
Two-tier rack (microgreens)
• Each shelf: strips/bars delivering 150–250 PPFD at tray height.
• 14–18 h photoperiod; track DLI by crop (radish vs basil differ).
• Keep fixtures clean for maximum output.
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MAINTENANCE
• Dust bars/drivers; keep intakes clear for cooling.
• Check connectors, dimmer pots, and link cables.
• Replace/rotate fixtures only if output drifts (use a PAR meter to confirm).
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TROUBLESHOOTING
• Leggy seedlings → too little blue/PPFD; lower light or increase power slightly.
• Tip burn/bleaching → PPFD too high or VPD too low; raise lamp, dim, improve airflow.
• Uneven growth → re-level fixture, adjust bar spacing, verify PPFD corners/edges.
• Slow greens → DLI too low; extend hours or increase PPFD modestly.
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SAFETY & COMPLIANCE
• Look for UL/ETL/CE marks; DLC Horticulture is a plus for rebates.
• Confirm IP rating if humidity is high (IP65+ preferred).
• Use proper gauges, breakers, and GFCI where required.
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COST-SAVING TIPS
• Buy high-efficacy fixtures (they pay back in kWh).
• Dim to PPFD/DLI—not always 100%.
• Keep fixtures clean; a dusty bar costs you PPFD and revenue.
• Stagger photoperiods to flatten peak load (if your tariff rewards it).
• Pair lights with right-sized dehumidifiers to stabilize VPD and reduce disease.
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QUICK BUYER’S CHECKLIST
□ PPF (µmol/s) and PPE (µmol/J) listed and credible
□ Uniform PPFD map provided (at realistic heights)
□ Dimming and group control supported
□ Driver brand and warranty length clear
□ IP rating and safety certifications shown
□ PAR meter on hand or borrow one to verify
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FAQS
Do I need far-red/UV?
Not to start. Full-spectrum + deep red works well. Add specialty channels later with a goal in mind.
What’s more important—watts or PPFD?
PPFD/DLI at the canopy. Watts only tell you input power; efficacy and distribution determine plant light.
How many hours per day should I run lights?
Use photoperiod to hit the DLI target for your crop while managing heat and power cost (greens often 16 h; fruiting 12–16 h).
Can I use one big light instead of two smaller ones?
You can, but two fixtures often give better coverage and redundancy.
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DISCLAIMER
Targets and examples are planning guides—adjust by crop variety, environment, and your measurements. Always verify electrical capacity, clearances, and safety standards. © 2025 Grow Lights for Indoor Farming Guide.