Grow Lights
Types • Spectrum • Timing
Grow lights allow growers to precisely control light intensity, spectrum, and timing when natural sunlight is limited, inconsistent, or unavailable. From seed-starting racks and grow tents to greenhouses and indoor farms, artificial lighting makes it possible to maintain healthy plant growth year‑round.
The key to success is matching light output to the plant’s growth stage. Seedlings require gentle but close light to prevent stretching, leafy crops thrive under steady vegetative intensity, and flowering or fruiting plants demand higher total daily light to support bloom formation and yield.
This guide explains the major grow light types, how spectrum and photoperiod affect plants, and how to choose fixtures that balance plant performance, energy efficiency, heat management, and usable growing space.
| Stage | Typical PPFD target* | Photoperiod (hours/day) | Notes |
|---|---|---|---|
| Seedlings / propagation | 100–300 | 14–18 | Keep lights close enough to prevent stretching. Gentle airflow helps strengthen stems. |
| Vegetative growth (leafy) | 200–500 | 14–18 | Great for herbs, greens, and transplants. Blue-rich or full-spectrum works well. |
| Flowering / fruiting | 500–900+ | 10–12 (many crops) | Higher intensity drives blooms and fruit set—watch heat, watering, and nutrition. |
*Targets vary by crop, CO₂ level, temperature, and cultivar. Start lower and increase if plants respond well (thicker stems, tighter internodes, deeper green without burn).
Light intensity and spacing directly affect growth rate and harvest size. Use these tools to estimate output and dial in plant density under lights.
Modern horticulture LEDs are efficient, run cooler than HID, and can be built as bars (even canopy coverage) or boards (compact fixtures). Look for full-spectrum (white + some deep red) and good thermal management. Dimmable drivers are a big plus.
Fluorescents are a proven, low-cost choice for seed starting and light vegetative growth. They don’t penetrate deeply into thick canopies, so they’re less ideal for heavy flowering/fruiting.
HID systems were the commercial standard for decades. Metal Halide (MH) is blue-leaning (veg), and HPS is red/orange-leaning (flower). They produce more radiant heat, which can help in cold spaces but becomes a challenge in warm rooms.
CMH (also called LEC) is a type of HID with a broader spectrum than HPS, often praised for plant quality and color rendering. It still runs hot compared to LED, but many growers like the canopy penetration and spectrum balance.
| Plant type | What they want most | Good light approach | Tips |
|---|---|---|---|
| Leafy greens (lettuce, kale, spinach) | Steady veg light, moderate intensity | Full-spectrum LED or T5 for racks | Cooler temps + strong airflow = tighter heads and better texture. |
| Herbs (basil, cilantro, mint) | Moderate-high veg light | Full-spectrum LED | Basil handles higher PPFD than many herbs—watch tip burn from heat or EC. |
| Seedlings / transplants | Compact growth, strong stems | T5/LED close to canopy | If seedlings stretch, increase intensity or move lights closer. |
| Fruiting crops (tomato, pepper, cucumber) | High intensity + longer DLI | High-output LED bars / quality HID | Fruit set improves with stable temps, airflow, and consistent watering. |
| Flowering ornamentals | Photoperiod control + intensity | LED with timer control | Many ornamentals are day-length sensitive—timers are your friend. |
| Technology | Advantages | Disadvantages |
|---|---|---|
| LED | Most efficient; low heat; long life; full-cycle capable; dimmable | Higher upfront cost; quality varies; “hot spots” if coverage is poor |
| Fluorescent | Great for seedlings; inexpensive; easy to hang close | Lower intensity; weaker penetration; bulbs age and need replacing |
| HID (HPS/MH) | High intensity; strong penetration; proven results | High heat; higher electricity; ventilation needed; bulbs replaced |
| CMH/LEC | Broad spectrum; good plant quality; strong penetration | Heat; power use; bulb cost/replacement |
Below are widely used suppliers across hobby and commercial grows. Choose based on your footprint and goals (seedlings vs fruiting). Always compare coverage area, wattage, and PPFD maps.
Optimize inputs under controlled conditions—measurement, timing, and ROI decisions.
High-yield leafy crops under lights—spacing, airflow, and harvest cadence.
Designing productive indoor systems—light planning, climate control, and layout.
Maximize canopy efficiency and airflow while preventing disease pressure.
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| Feature | LED | HID | Fluorescent |
|---|---|---|---|
| Efficiency | High | Medium | Low |
| Heat Output | Low | High | Low |
| Lifespan | 50,000+ hrs | 10,000 hrs | 8,000 hrs |
| Best For | Full cycle growing | High-intensity flowering | Seedlings & leafy greens |
A quality full-spectrum LED is the most versatile choice for home growing because it’s energy-efficient, runs cooler than HID, and can support seedlings through fruiting if you buy enough intensity and coverage. For simple seed-starting shelves, T5/LED “shop light” style fixtures can also work well.
Leggy seedlings usually mean insufficient light intensity (or the light is too far from the canopy). Move the fixture closer (without overheating), increase brightness, and keep the photoperiod consistent. Gentle airflow (a small fan) also helps seedlings build thicker stems.
Most seedlings and leafy crops do well with 14–18 hours per day. Fruiting and flowering crops often perform best with strong intensity and a consistent schedule (many growers use 12–16 hours, depending on the plant). Use a timer so plants get reliable “days” and “nights.”
Yes. Vegetative (leafy) growth typically benefits from a spectrum with more blue content and moderate intensity, while flowering and fruiting responds well to higher intensity and more red content. Most modern full-spectrum LEDs cover both stages—the bigger difference in results is often intensity (PPFD/DLI), not color alone.
PPFD is how much usable light hits your plant canopy at a moment in time (µmol/m²/s). DLI is the total light your plants receive in a day—PPFD multiplied by the number of light hours. Plants respond strongly to DLI because it reflects the day’s total “light budget.”
It depends on the fixture and plant stage. Seedlings usually like lights closer to prevent stretching, while high-power LEDs for fruiting are often kept higher to improve uniformity and prevent stress. Start with the manufacturer’s hanging height, then adjust based on plant response (stretching = too weak/far; bleaching/curling = too intense/close).
Yes, but fruiting crops need high light intensity, good airflow, and stable temperatures. Expect stronger fixtures (often LED bars/boards designed for tents or rooms), and plan for more frequent watering and feeding. Pollination support (shaking flowers, gentle airflow, or hand pollination) can improve fruit set indoors.
Absolutely. T5 fluorescent and LED shop-light style fixtures are excellent for seedlings, clones, microgreens, and leafy greens on racks. They typically don’t have enough intensity and canopy penetration for heavy flowering and fruiting, but they’re a budget-friendly win for propagation and leafy production.
Start with your goal and footprint: Seedlings/greens = moderate intensity over a shelf (often small LED bars or shop-light style fixtures). Flowering/fruiting = higher-output LEDs sized to your tent/bed area with published coverage and PPFD data. Choose fixtures with a reliable driver, good heat management, and (ideally) dimming.
Commonly used options include LED brands like HLG, Fluence, Gavita, Spider Farmer, Mars Hydro, AC Infinity, ViparSpectra, and retailers like GrowGeneration, Hydrobuilder, HTG Supply, plus local hydroponic stores (great for parts and advice). Compare coverage area, wattage, and PPFD maps before buying.
