DISCLAIMER: Cannabis cultivation is illegal in many jurisdictions. This guide is for educational purposes only and does not constitute legal advice. Always check and comply with your local laws and regulations before cultivating cannabis.
Lighting is the single largest equipment investment for indoor cannabis cultivation and one of the most important factors determining yield, potency, and quality. This page helps you choose the right light, size it correctly for your grow space, and select the accessories needed for a complete setup. Whether you are buying your first light for a 2x2 tent or outfitting a commercial room, this guide focuses on the practical purchasing decisions — not the underlying science.
Note: For the science of lighting (PPFD, DLI, PAR spectrum, light cycles), see the complete Lighting Systems guide.
| Factor | LED | HPS | CMH/LEC | CFL |
|---|---|---|---|---|
| Upfront cost | Moderate to high | Low to moderate | Moderate | Very low |
| Running cost | Lowest | Highest | Moderate | Low |
| Lifespan | 50,000+ hours | 10,000-18,000 hours (bulb replacement needed) | 15,000-20,000 hours | 8,000-10,000 hours |
| Heat output | Low to moderate | Very high | Moderate | Very low |
| Spectrum quality | Tunable, full-spectrum available | Heavy red/orange, weak blue | Excellent full-spectrum, high UVB | Variable, generally weak |
| Efficiency (umol/J) | 2.4-3.2+ | 0.9-1.7 | 1.6-2.2+ | 0.5-1.0 |
| Best use case | All stages, all grow spaces | Flowering stage, large spaces, budget builds | All stages, quality-focused builds | Seedlings, clones, mother plants only |
LED technology has matured to the point where it is the default recommendation for most growers. The market, however, varies enormously in quality.
Pros:
Cons:
What to look for when buying:
HPS was the industry standard for decades and still has a place in certain setups, particularly for budget-conscious growers or as a supplemental flowering light.
Pros:
Cons:
When it still makes sense:
Ballast types:
Bulb replacement schedule: HPS bulbs lose 10-15% of their output after approximately 10,000 hours of use. Replace bulbs every 1-2 grow cycles for best results. Keep spare bulbs on hand. Popular bulb brands include Hortilux, Philips, and Ushio.
CMH (also marketed as LEC by some manufacturers) uses a ceramic arc tube that produces a spectrum much closer to natural sunlight than HPS.
Pros:
Cons:
Best use case: CMH is an excellent choice for growers who want spectrum quality close to sunlight without the heat of HPS. Many growers use CMH for vegetative growth and switch to HPS for flowering, though a single CMH can handle both stages. The most common wattages are 315W (covers 3x3) and 630W (covers 4x4).
CFLs have a very narrow use case in cannabis cultivation.
Only appropriate for:
CFLs do not produce enough intensity to flower cannabis plants effectively. A single CFL may work for a single plant in a 2x2 space, but expect airy buds and long internodal spacing. Budget growers should consider a small LED panel instead for any stage beyond seedlings.
Getting the right light size for your grow space is critical. Too little light and yields suffer. Too much light in a small space creates heat management nightmares and wasted capacity.
| Grow Space | Minimum Actual Watts | Recommended Actual Watts | Light Type |
|---|---|---|---|
| 2x2 ft (0.37 m²) | 60-80W | 100-120W | Small LED bar or quantum board |
| 2x4 ft (0.74 m²) | 120-150W | 200-240W | Medium LED bar |
| 3x3 ft (0.84 m²) | 150-180W | 240-300W | LED bar or 315W CMH |
| 4x4 ft (1.5 m²) | 300-350W | 450-500W | Large LED bar or 600W HPS |
| 4x8 ft (3 m²) | 600-650W | 900-1000W | Two 4x4 LED bars or 1000W HPS |
| 5x5 ft (2.3 m²) | 400-450W | 600-650W | Large LED bar or 630W CMH |
| 6x6 ft (3.3 m²) | 600-700W | 900-1000W | Two LED bars or 1000W HPS |
How to calculate light needs:
Hanging height guidelines:
| Light Type | Seedling/Clone | Vegetative | Flowering |
|---|---|---|---|
| LED (bar-style) | 24-30 inches | 18-24 inches | 12-18 inches |
| LED (quantum board) | 24-30 inches | 18-24 inches | 12-18 inches |
| HPS 400W | 24-30 inches | 20-26 inches | 16-22 inches |
| HPS 600W | 30-36 inches | 24-30 inches | 18-24 inches |
| HPS 1000W | 36-42 inches | 30-36 inches | 24-30 inches |
| CMH 315W | 18-24 inches | 14-20 inches | 12-18 inches |
| CMH 630W | 24-30 inches | 18-24 inches | 14-20 inches |
Tip: Always start lights higher than recommended and gradually lower them while monitoring for light stress (bleached or curled leaf tips, upward leaf curling). Every light is different — manufacturer height recommendations are starting points, not absolutes.
The LED market in particular ranges from excellent to outright scams. Here is what to expect at each price tier.
| Tier | Price Range | What to Expect | Typical Use |
|---|---|---|---|
| Budget | $50-150 | Unknown diode brands, generic drivers, inflated "equivalent" wattage claims, thin or no warranty (0-1 year), no independent PPFD data, basic spectrum, plastic or thin aluminum housing | 2x2 tent, first-time grower testing the waters, seedling/clone station |
| Mid-range | $150-400 | Samsung LM301B or LM301H diodes, Mean Well or comparable driver, honest watt draw specs, 2-3 year warranty, some independent PPFD data available, bar-style or quality quantum board design, dimmable | 2x4 to 4x4 tent, serious home grower, best value segment |
| Premium | $400-800 | Samsung LM301H EVO diodes, Mean Well driver, full-spectrum with added red/UV, 5-year warranty, independently verified PPFD maps, quality aluminum construction, daisy-chain capable, smart controls optional | 4x4 to 5x5, quality-focused grower, long-term investment |
| Commercial | $800+ | Top-bin diodes, programmable spectrum, networked controllers, 5+ year warranty, DLC certification, third-party testing data, modular designs for large rooms, tech support | 4x8 and larger, commercial facilities, multi-light installations |
Warning: Be extremely cautious of lights on Amazon or AliExpress claiming "10000W" or similar absurd equivalent wattages for under $100. These are almost always low-quality blurple (red/blue) or white panel lights using cheap no-name diodes that degrade within months. If a deal seems too good to be true, it is.
Red flags when shopping:
Use this checklist before purchasing any grow light:
| Accessory | Purpose | Budget Option | Premium Option |
|---|---|---|---|
| Digital timer | Light cycle control — critical for triggering and maintaining flowering | $10-15 mechanical plug timer | $30-50 smart WiFi timer with app control and battery backup |
| Light hangers | Adjustable height for light positioning as plants grow | Ratchet straps $10 for a 4-pack | Cable pulley systems $30 for smoother, finer height adjustment |
| Light movers | Even coverage across canopy by moving light in a circular or linear pattern | $40-60 linear rail mover | $100-150 rotational/orbital mover |
| Reflective material | Maximize light utilization by reflecting spill light back onto plants | Mylar film $15/roll (90-95% reflectivity) | Flat white paint — cheaper, easier to apply, 85-90% reflectivity |
| Light meter | Verify PPFD at canopy level to ensure even coverage and correct intensity | $20 basic PAR meter app + phone sensor (approximate) | $200+ quantum sensor (Apogee MQ-500 series) for accurate readings |
| IR thermometer | Check leaf surface temperature to detect heat stress from lights | $15-25 infrared thermometer gun | $50-100 thermal camera attachment for smartphone |
A reliable timer is not optional — cannabis flowering is triggered and maintained by strict light cycles. A single missed dark period during flowering can cause hermaphroditism or revegetation.
Mechanical timers ($10-15): Simple dial timers with trippers. Reliable, no batteries needed, but less precise and can fail if the power goes out.
Digital timers ($20-35): LCD display with battery backup. More precise, programmable for complex schedules, battery maintains programming during outages. Recommended for most growers.
Smart WiFi timers ($30-50): App-controlled, can monitor and adjust schedules remotely, some integrate with environmental controllers. Useful if you travel or want logging capability.
Warning: Never rely on a smart plug without battery backup as your sole timer. If WiFi drops or the app crashes, your light cycle is disrupted. Always have a battery-backed digital timer as a fallback.
Light movers move your grow light across the canopy, either in a linear track or circular pattern.
Pros:
Cons:
Verdict: Light movers are most beneficial for HPS and single-point light sources. Modern bar-style LED lights spread light so evenly across their footprint that movers offer diminishing returns. For a 4x8 or larger space, a mover may still be worthwhile even with LEDs.
Maximizing light efficiency means capturing light that would otherwise hit the walls and reflecting it back onto plants.
| Material | Reflectivity | Cost | Notes |
|---|---|---|---|
| Mylar film | 90-95% | $15-25/roll | Best reflectivity, but wrinkles easily and can create hot spots if not stretched flat |
| Flat white paint | 85-90% | $20-30/gallon | Easiest to apply, most even reflection, no hot spots. Use flat/matte, not glossy |
| Black and white panda film | 85-90% (white side) | $30-50/roll | Durable, easy to install, doubles as a light-proof barrier on the black side |
| Foylon | 85-95% | $50-80/roll | Fabric-like, tear-resistant, excellent reflectivity, most expensive option |
| Aluminum foil | 80-85% | Very cheap | Creates hot spots and uneven reflection. Not recommended beyond emergency use |
Tip: Flat white paint is often the best choice for permanent grow rooms. It is cheap, easy to apply, provides even reflection without hot spots, and does not degrade over time like Mylar can.
Every watt of electricity your light consumes eventually becomes heat. Managing this heat is essential for plant health and determines your ventilation and cooling requirements.
| Technology | Heat Output | 4x4 Space Heat Load | Ventilation Impact |
|---|---|---|---|
| LED (500W) | ~1,705 BTU/hr | ~1,700 BTU/hr | Low — standard inline fan usually sufficient |
| HPS 600W | ~2,050 BTU/hr (+ radiant IR to canopy) | ~2,050 BTU/hr | High — requires 400+ CFM exhaust, possibly AC |
| HPS 1000W | ~3,410 BTU/hr (+ radiant IR to canopy) | ~3,410 BTU/hr | Very high — almost certainly requires AC |
| CMH 315W | ~1,100 BTU/hr (with ballast) | ~1,100 BTU/hr | Moderate — good passive or low-speed exhaust |
| CMH 630W | ~2,200 BTU/hr (with ballast) | ~2,200 BTU/hr | Moderate to high — active exhaust recommended |
Note: While all technologies produce 3.41 BTU per watt of electricity consumed, HPS produces significantly more radiant (infrared) heat that directly heats leaf surfaces and canopy air. LEDs produce mostly convective heat that rises from the fixture itself. This means a 500W LED will raise room temperature less than a 500W HPS in practice.
Greenhouse growers get free sunlight, but natural light is often insufficient for cannabis, especially in winter months, cloudy climates, or early/late in the growing season.
| Scenario | Recommended Light | Notes |
|---|---|---|
| Winter vegetative boost | LED bar lights at 40-60% power | Extends day length to 16+ hours; low heat is an advantage in already-cool greenhouse |
| Flowering supplement (cloudy climate) | Full-power LED bars | Compensates for low natural DLI during flowering months |
| Year-round propagation area | CFL or small LED panel | Low-intensity light for seedlings and clones separate from main greenhouse |
| Large commercial greenhouse | Top-mounted LED bars or intercanopy lighting | Professional installations use overhead supplemental lighting plus side lighting for lower canopy |
Tip: Greenhouse growers should invest in a PAR meter to measure actual DLI inside the greenhouse. This data tells you exactly how much supplemental light is needed and when you can turn lights off to save electricity. A $200 quantum sensor pays for itself quickly in electricity savings.
See Also: /cultivation/indoor/lighting | /cultivation/equipment/environment | /cultivation/equipment/index | /cultivation/indoor/grow-guide | /cultivation/greenhouse