Cannabis Grow Lights Guide

Q: What is the best grow light for cannabis?

LED grow lights are the best overall choice for cannabis in 2026. They offer the highest efficiency (up to 3.0 umol/J), produce less heat, last longer, and reduce electricity costs compared to HPS or CMH. Samsung LM301 diode-based LEDs are the current gold standard.

Q: How many watts do I need to grow cannabis?

For LED lights, aim for 30-40 watts of actual draw per square foot of canopy. A 4x4 foot tent needs a 480-640 watt LED. For HPS, use 50 watts per square foot. These are general guidelines — light quality and efficiency matter more than raw wattage.

Q: What light schedule should I use for cannabis?

For photoperiod cannabis: use 18/6 (18 hours on, 6 off) during vegetative growth, then switch to 12/12 to trigger flowering. For autoflowers: 18/6 or 20/4 throughout their entire lifecycle works well.

Q: What is DLI and why does it matter?

DLI (Daily Light Integral) measures the total amount of photosynthetically active light a plant receives per day, measured in mol/m²/day. Cannabis thrives at 40-65 DLI during flowering. DLI accounts for both light intensity and duration.

Q: Is LED better than HPS for growing cannabis?

In most cases, yes. Modern LEDs are more energy efficient, produce less heat, last 50,000+ hours, and offer full spectrum light. HPS still has advantages in cold climates where the heat output is beneficial, and for growers on a tight budget.

Q: How far should grow lights be from cannabis plants?

LED lights: 12-24 inches during veg, 8-18 inches during flower (varies by intensity). HPS 600W: 16-24 inches. HPS 1000W: 24-30 inches. Always check manufacturer recommendations and watch for light stress signs.

Q: Do cannabis plants need darkness?

Photoperiod cannabis plants require 12 hours of uninterrupted darkness to flower. During veg, 6 hours of dark is standard but not strictly required. Autoflowers do not need dark periods but benefit from 4-6 hours of rest for plant recovery.

Q: What is PAR and PPFD in cannabis growing?

PAR (Photosynthetically Active Radiation) is the range of light wavelengths plants use (400-700nm). PPFD (Photosynthetic Photon Flux Density) measures the intensity of PAR light reaching the canopy in micromoles per square meter per second (umol/m²/s). Target 600-900 PPFD during flower.

Q: Can I use regular light bulbs to grow cannabis?

Regular household bulbs do not provide enough intensity or the right spectrum for cannabis. CFL bulbs can work for seedlings and very small grows, but you will get much better results with purpose-built cannabis grow lights.

Cannabis grow lights are the engine of every indoor operation. Light quality, intensity, and spectrum directly determine yield and potency.

This guide compares LED, HPS, and CMH lights, then covers schedules, DLI, and budget setups for both autoflower and feminized seed grows.

LED vs HPS vs CMH Comparison

This side-by-side comparison covers the three main grow light technologies. Use it to make an informed decision.

Feature	LED	HPS	CMH / LEC
Efficiency	2.5-3.0 umol/J	1.5-1.7 umol/J	1.7-2.0 umol/J
Heat output	Low-Moderate	Very High	High
Spectrum	Full spectrum	Red/Orange heavy	Full spectrum, UV
Lifespan	50,000-100,000 hrs	10,000-24,000 hrs	20,000-30,000 hrs
Upfront cost	$200-800+	$100-300	$200-500
Running cost	Low	High	Moderate
Coverage (4x4)	400-600W draw	600-1000W	2x 315W (630W)
Bulb replacement	Not needed	Every 2-3 grows	Every 3-4 grows
Best for	All growers, efficiency	Budget, cold rooms	Quality-focused

In 2026, LED technology is the clear winner. Energy savings alone pay for the higher upfront cost within 1-2 grows.

Understanding PAR, PPFD, and Light Spectrum

These metrics determine how much usable light your plants actually receive. Understanding them helps you choose the right light.

PAR (Photosynthetically Active Radiation)

PAR spans from 400nm (blue) to 700nm (deep red). Not all light wavelengths are equally useful for cannabis plants.

PPFD (Photosynthetic Photon Flux Density)

PPFD measures how many PAR photons hit a square meter per second. This is the most important metric for grow lights.

Target these PPFD values for cannabis.

Seedlings: 200-400 umol/m²/s for gentle early growth.
Vegetative growth: 400-600 umol/m²/s for strong development.
Flowering: 600-900 umol/m²/s for maximum bud production.
Flowering with CO2: 900-1500 umol/m²/s for enhanced yields.

Light Spectrum

Blue light (400-500nm) promotes compact veg growth. Red light (620-700nm) drives flowering and bud development.

Full-spectrum LEDs perform best across all stages of the cannabis lifecycle.

Daily Light Integral (DLI) Explained

DLI measures total PAR light over 24 hours in mol/m²/day. PPFD tells you intensity; DLI gives the complete picture.

DLI Formula: PPFD x hours of light x 0.0036 = DLI

Target these DLI values for cannabis.

Seedlings: 12-20 mol/m²/day for healthy starts.
Vegetative growth: 25-40 mol/m²/day for vigorous development.
Flowering: 40-65 mol/m²/day for maximum bud production.

Example: 700 PPFD x 12 hours x 0.0036 = 30.2 DLI. Below the 40-65 target, suggesting higher intensity or longer hours for autoflowers on 18/6.

DLI is especially useful for autoflower growers on 18-20 hour schedules. Longer light means optimal DLI with lower-intensity lights.

Light Schedules for Cannabis

Your schedule depends on seed type. Each has specific purposes and trade-offs.

Schedule	Light / Dark	Use For	Notes
18/6	18 on / 6 off	Photoperiod veg, autoflowers	Standard, good energy balance
20/4	20 on / 4 off	Autoflowers	More DLI, slightly higher cost
24/0	24 on / 0 off	Autoflowers (debated)	Max DLI but plants may need rest
12/12	12 on / 12 off	Photoperiod flowering	Required to trigger flowering

The 18/6 to 12/12 switch is non-negotiable for photoperiods. Ensure the dark period is completely uninterrupted.

For autoflowers, 18/6 is most popular and cost-effective. Some growers prefer 20/4 for slightly faster growth.

LED Grow Lights for Cannabis

Modern full-spectrum LEDs deliver more usable light per watt than any other technology. They run cooler and last for years.

Look for these features when shopping.

Diode quality: Samsung LM301B and LM301H are the industry standard.
Driver quality: Meanwell drivers are reliable and highly efficient.
Efficiency: Look for 2.5+ umol/J, with top-tier exceeding 2.8.
Spectrum: Mix of 3000K and 5000K diodes plus 660nm red.
Dimmability: Essential for seedlings and managing summer heat.

Budget LEDs start around $200 CAD for a 2x2 tent. Quality 4x4 lights run $400-700 CAD. Avoid cheap unbranded LEDs.

HPS Grow Lights for Cannabis

HPS lights have been the cannabis standard for decades. While surpassed by LEDs, they remain viable for budget setups.

HPS offers these key advantages.

Low upfront cost: A complete 600W setup costs under $150 CAD.
Proven results: Decades of successful grows confirm their reliability.
Beneficial heat: In Canadian basements during winter, HPS reduces heating needs.
Simple setup: No electronics to configure, just plug in and grow.

Main drawbacks are high electricity cost, summer heat, and limited spectrum. Bulbs need replacing every 2-3 grows.

CMH Grow Lights for Cannabis

Ceramic Metal Halide sits between HPS and LED in performance. It produces a remarkably natural spectrum including UV light.

Here is why some growers prefer CMH.

Excellent spectrum: Closest to natural sunlight of any HID light type.
Better than HPS: About 10-15% more efficient with better colour rendering.
Good heat balance: Less heat than HPS but enough to warm Canadian spaces.
Proven flower quality: Many craft growers prefer CMH for terpene production.

A 315W CMH covers a 3x3 foot area. Two fixtures provide excellent 4x4 tent coverage.

Light Distance and Intensity

Correct light distance is critical. Too close causes bleaching; too far wastes energy and stretches plants.

Use this table for recommended hanging heights.

Light Type	Seedling Distance	Veg Distance	Flower Distance
LED (200-300W)	24-30 inches	18-24 inches	12-18 inches
LED (400-600W)	30-36 inches	20-28 inches	14-22 inches
HPS 400W	24-30 inches	16-22 inches	12-18 inches
HPS 600W	30-36 inches	20-26 inches	16-24 inches
CMH 315W	24-30 inches	18-24 inches	14-20 inches

Signs of Too Much Light

Bleached tips: White or pale tips on upper leaves signal light burn.
Taco-ing: Leaves curling upward at the edges to escape intensity.
Brown spots: Yellow or brown spots on the upper canopy only.
Fox-tailing: Elongated bud growth closest to the light source.

With dimmable LEDs, start at 50% for seedlings and increase gradually as plants mature.

Budget Grow Light Setups for Canada

Great cannabis does not require expensive lighting. Here are setups at three price points.

Budget ($100-200 CAD)

Light: 100-150W LED panel from a reputable brand.
Coverage: 2x2 foot space for 1-2 plants.
Best for: Autoflower seeds in a small closet or tent.
Electricity: Approximately $15-25 CAD per month.

Mid-Range ($300-500 CAD)

Light: 240-320W LED bar-style with Samsung diodes.
Coverage: 3x3 to 4x4 foot tent for 2-4 plants.
Best for: Any seed type including feminized seeds.
Electricity: Approximately $25-45 CAD per month.

Premium ($500-800+ CAD)

Light: 480-640W top-tier LED with highest efficiency diodes.
Coverage: Full 4x4 to 5x5 foot area for 4+ plants.
Best for: Maximizing yield per square foot with even coverage.
Electricity: Approximately $40-65 CAD per month.

Canadian electricity rates vary by province. Ontario, Quebec, and BC have lower rates, making LED efficiency important everywhere.

Common Lighting Mistakes

Even experienced growers make lighting errors. Avoiding these protects your plants and wallet.

Watch out for these frequent pitfalls.

Buying on advertised wattage: Cheap LEDs misrepresent wattage. Check actual wall draw.
Wrong distance: Use a PPFD meter or manufacturer guidelines throughout the grow.
Ignoring edge drop-off: PPFD decreases at the edges, so center your plants.
Light leaks during dark: Even small leaks cause hermaphroditism or reveg.
Full power on seedlings: Start at 40-50% intensity and increase gradually.
Ignoring electricity costs: Calculate monthly cost before choosing your light setup.

Planning your lighting setup before starting saves money and produces better results from the first harvest.

Frequently Asked Questions

What is the best grow light for cannabis?+

LED grow lights are the best overall choice in 2026. They offer the highest efficiency (up to 3.0 umol/J), less heat, and lower electricity costs.

How many watts do I need to grow cannabis?+

For LEDs, aim for 30-40 watts per square foot. A 4x4 tent needs 480-640W. Efficiency matters more than raw wattage.

What light schedule should I use for cannabis?+

Photoperiod: 18/6 for veg, then 12/12 for flowering. Autoflowers: 18/6 or 20/4 throughout their entire lifecycle.

What is DLI and why does it matter?+

DLI measures total PAR light per day in mol/m²/day. Cannabis thrives at 40-65 DLI during flowering. It accounts for both intensity and duration.

Is LED better than HPS for growing cannabis?+

In most cases, yes. LEDs are more efficient, cooler, last 50,000+ hours, and offer full spectrum. HPS still suits cold climates and tight budgets.

How far should grow lights be from cannabis plants?+

LED: 12-24 inches during veg, 8-18 inches during flower. HPS 600W: 16-24 inches. Always follow manufacturer recommendations.

Do cannabis plants need darkness?+

Photoperiod plants require 12 hours of uninterrupted darkness to flower. Autoflowers benefit from 4-6 hours of rest but do not require it.

What is PAR and PPFD in cannabis growing?+

PAR is the light wavelength range plants use (400-700nm). PPFD measures PAR intensity at the canopy. Target 600-900 PPFD during flower.

Can I use regular light bulbs to grow cannabis?+

Regular household bulbs lack the intensity and spectrum cannabis needs. Purpose-built grow lights are necessary for healthy growth.

Got your lights ready? Browse our premium cannabis seeds for indoor growing.

Feminized Seeds Autoflower Seeds

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Written by

Sarah Mitchell

Head Cultivator & Grow Expert

Cannabis cultivation specialist with 12+ years of hands-on growing experience across indoor, outdoor, and greenhouse environments in Canada.

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