The beauty of growing cannabis indoors is the fact that you get to use grow lights, meaning your plants get plenty of PAR-rich, intense light. There are so many cannabis grow lights available in different shapes, sizes and power usage. Knowing which lights are best and knowing how much light to give your plants at each stage will be the key to an incredible harvest.

In this article, I explain why cannabis grow lights are essential for cultivation, the different types of grow lights available to buy, how to choose the best grow light, how to set up your lights correctly, and the best practices for growing with LED!

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Why Cannabis Grow Lights Are Essential for Indoor Growing

Even though cannabis plants are referred to as weed because they can grow in most conditions, they still require the correct spectrum, intensity and photosynthetically active radiation (PAR) levels.

The cannabis grow light you use will determine plant growth, yields, and bud quality, but successful harvests also depend on knowing how to grow autoflower indoors and creating the correct environment. Below explains how grow lights affect a cannabis plant’s development, the different light regimes for vegetative and flowering stages, and common mistakes beginners make with indoor grow lights.

comparison light spectrum guide for growth

How Grow Lights for Cannabis Affect Plant Growth and Yields

Outdoors, cannabis plants thrive in sunlight, as they have access to the full spectrum required for growth and flowering. As an indoor grower, it is your job to mimic outdoor conditions and provide your plants with the same spectrum of light.

Cannabis plants require light to convert energy and perform photosynthesis
Grow lights provide the perfect light spectrum to promote root development
Grow lights create the light and darkness periods plants need for each stage, although understanding the correct light schedule for autoflowers is important because autoflowering genetics do not rely on a traditional flowering cycle.
Light intensity will determine how big and fast the plants grow during vegetation
Grow lights are responsible for internodal spacing, stem and branch thickness

Understanding Cannabis Growing Lighting for Veg and Flower Stages

Cannabis is phototropic, meaning it responds to light, either growing vegetatively or inducing flowering and producing buds. All you need to do is set your grow timer to either 18/6 or 12/12.

The vegetative stage begins when you germinate your seeds, and after 2 weeks, your plants are vegetating and producing 5-fingered fan leaves. For growers who are new to indoor cultivation, choosing autoflower seeds for beginners can make learning how to manage light intensity and schedules much easier. During this stage, your plants are focused on root development, stems, foliage and developing nodes and internodes.

Vegetating plants require high ratios of blue light during 18/6
The blue light spectrum is between 400 and 500 nm
Blue light creates short internodal spacing and stocky plants

The flowering stage comes after the veg stage, and once you are happy with how tall, wide or trained your plants are, you can set your grow timer to 12/12. The longer period of darkness tricks plants into flowering in the same way they do over Summer.

The first 2-3 weeks of 12/12 are when the cannabis plant will stretch
Cannabis plants require red light and a spectrum between 600-700nm
Red light is responsible for inducing flowers and developing buds, making it especially important when growing high THC autoflower seeds that are bred for maximum resin and cannabinoid production.

Common Beginner Mistakes with Indoor Grow Lights for Cannabis

Below are 5 common mistakes a beginner may make when deciding which grow light is best for them, as well as potential mistakes when hanging the light.

#1 – Buying a light based on lumens instead of PAR. Lumens are not important.
#2 – Hanging your grow light too far away causes lanky and tall plants
#3 – Not hanging the grow light horizontally, causing uneven light to spread
#4 – Using grow lights that contain low levels of blue and red light
#5 – Using grow lights that produce a low PAR and PPFD output

Types of Growing Lights Cannabis Beginners Should Know

Once you do a bit of research on the different cannabis lights available, you will soon realise that there are different types of light, ranging from LED, HID and fluorescents. Some are best suited for seedlings, clones and young plants, whilst others are required to produce intense light and the desired yields. Below breaks down the different choices and what to consider when deciding which type of grow light is best for you.

LED Cannabis Grow Lights vs HID vs Fluorescent Lights

LEDs and compact fluorescent (CFL) lights are both popular amongst home growers due to their efficiency and low heat output. However, when light intensity and PAR levels are what count, you have to make a clear separation between the two:

Feature	LED	HID (HPS/MH)	Fluorescent (CFL/T5)
Energy Efficiency	Excellent	Moderate	Good
Heat Output	Low	High	Low
Yield Potential	Excellent	Excellent	Poor
Lifespan	50,000+ Hours	10,000-20,000 Hours	8,000-20,000 Hours
Best For	All Stages	Veg & Flower	Seedlings & Clones
Running Cost	Low	High	Low
Beginner Friendly	Yes	Moderate	Yes

LED Cannabis Grow Lights

LED grow lights produce the optimal spectrum and PAR levels for big yields, which is why they are often the preferred choice when growing the highest yielding autoflowers indoors.
LED lights can be adjusted, allowing you to adjust light levels during each stage
Different LED models are ideal to fit inside a grow tent with ease
LED grow lights are full spectrum, so there is no need to supplement the light
You can buy small-sized LED lights, making them perfect for seedlings and clones
LED grow lights can range in power usage from 20W to 1000W

Fluorescent Cannabis Grow Lights

CFL lights are rich in blue light (6400k) and promote healthy growth
CFL lights are only suitable for seedlings, clones and infant plants
They are available to buy as large bulbs or in T5 strip light form
CFL lights use very little power, ranging from 20-250W
CFL grow lights can be bought as blue or red dominant
They do not contain enough intensity or PAR to produce a good yield

Will LED Aquarium Lights Grow Cannabis Successfully?

Unfortunately, not as you would like; however, as mentioned above, these grow light levels work well for seedlings, clones, and vegetating infant plants. Once your cannabis plants enter the vegetative period, they will require greater levels of PAR and intensity.

LED aquarium grows lights produce a gentle, soft light that may be optimal for an aquarium; however, for cannabis cultivation, they are not in the equation when discussing powerful grow lights.

Pros and Cons of LED Grow Lights

The best piece of advice I could give a beginner grower is to spend their money wisely and only buy LED grow lights. Below are the pros and cons of using LED grow lights, along with key considerations.

The Pros

LED grow lights can be adjusted, reducing energy usage and light intensity
LED lights can be bought in small or large sizes, making them practical for home growers
They are manufactured with the optimal full spectrum required for veg and flower
LED lights use far less electricity than high-pressure sodium and metal halide lights
The amount of heat produced by LED lights is far lower compared to HID lighting
You can foliar spray your plants without worrying about exposed bulbs

The Cons

Some LED lights use internal cooling fans, which can collect dust and make noise
Not all LED lights have a good amount of light spread, requiring more lights
Some LED models can be too large to fit inside a small grow tent or space
Yields can be lower if the hanging distance is not correct
LED lights are expensive compared to HID lights

How to Choose the Best Grow Lights for Cannabis

Before you make a final decision, it is well-advised to take the time to research each grow light and check for specific information. You can create a short list of the best lights based on PAR output, the best LED grow lights, and the best grow lights for large grow spaces.

How Much Light Cannabis Plants Need Indoors

Whilst it is true that the more intensity and PAR your grow light possesses, the better the outcome will be, cannabis plants require different levels of light during their lifecycle.

Many growers also track DLI for autoflowers to calculate the total amount of light their plants receive throughout the day.

If you check the grow light specifications, you should be able to see the light’s efficacy and the PAR it produces, measured in µmol/m²/s. Understanding PPFD for autoflowers will help you determine whether your lighting setup is delivering enough usable light.

Growth Stage	PPFD (µmol/m²/s)	Light Cycle	Recommended Spectrum
Seedling	100-300	18/6	Blue-rich
Early Vegetative	300-500	18/6	Blue-rich
Late Vegetative	500-600	18/6	Full Spectrum
Early Flowering	600-800	12/12	Red-rich
Late Flowering	800-1050	12/12	Red-rich Full Spectrum

Best LED Grow Lights for Cannabis Beginners

A grow light can be an expensive investment; however, it is worth every penny once you can grow incredible resin-covered plants and cup-winning cannabis buds. The best advice I can offer you on LED grow lights is to thoroughly check and compare different brands. If you are growing autos, our guide to choosing the best grow light for autoflower plants explains what features to prioritise.

Always look to see the µmol/m²/s rating and if the light competes with other brands
Avoid cheap Chinese-made grow lights that use noisy internal fans
Find a light that has an adjustable dimmer so you can lower the light intensity
Check how much light the light offers and if it covers your grow space
Passive-cooled grow lights run silently and can keep cool

Choosing the Best Lights for Growing Cannabis in a 2×2, 3×3, or 4×4 Tent

Your options when working in a large grow space are LED, HPS, or metal halide.

Grow Tent Size	Recommended LED Wattage	Plant Capacity
2×2 ft	100-200W	1-2 Plants
3×3 ft	300-450W	2-4 Plants
4×4 ft	480-650W	4-6 Plants
5×5 ft	650-1000W	6-9 Plants

Setting Up Lights to Grow Cannabis Correctly

You may think that setting up your equipment and hanging the grow light takes a few minutes, and then you are ready to start growing! Hanging your grow lights correctly means considering the proper distance between the light and the canopy, setting up a light schedule using a timer, and preventing light burn, excessive stretching during the transition phase, and the signs and symptoms of heat stress.

Proper Distance Between Grow Lights Cannabis Plants Need

cannabis plants growth stage compared to light

Plant Stage	LED Distance	HID Distance
Seedlings	12-18 Inches	24-36 Inches
Vegetative	18-24 Inches	20-30 Inches
Flowering	18-24 Inches	18-24 Inches
High-Power LEDs (600W+)	24-30 Inches	N/A

Best Light Schedule for Cannabis During Veg and Flower

You will need to set your grow timer to different lighting schedules based on the plant’s stage. There are only 2 different light cycles required to veg and flower cannabis.

Seeding Stage – 18 hours of light and 6 hours of dark
Vegetation Stage – 18 hours of light and 6 hours of dark
Flowering Stage – 12 hours of light and 12 hours of dark

How to Prevent Light Burn, Stretching, and Heat Stress

Light burn and light stress are caused when grow lights are too close to the top of the canopy. Many growers feel that the closer the plants are, the better; however, you must consider temperature, humidity levels, and signs of heat and light stress. To To prevent light burn, raise the grow lights to 18-24 inches and maintain the best temperature and humidity for autoflowers throughout the grow cycle.

Cannabis plants that do not receive sufficient light intensity will stretch to grow as close to the light source as possible. Stretching results in lanky, tall plants during vegetative growth and causes plants to stretch too tall once flowering is induced.

Symptom	Light Stress	Heat Stress
White Bleached Tops	✓	✗
Yellow Upper Leaves	✓	✗
Taco Leaves	✓	✓
Crispy Leaf Edges	✗	✓
Airy Buds	✗	✓
Stunted Growth	✓	✓
Dry Buds	✓	✓

Signs of Heat Stress

Leaves will curl upwards and create a taco formation
The end of the leaflet becomes dry, brown and crispy
Growth seems slow and stunted
The foliage feels brittle
Buds develop with an airy and elongated formation
Terpenes can be affected by heat stress

Proper airflow is equally important, which is why every indoor grower should understand cannabis grow room ventilation and air exchange.

Signs of Light Stress

The top of the plants will turn albino white, pale or yellow
Top colas will display bleached white buds
Leaves will taco and curl inwards
Yields will be lower, and the buds may feel dry to the touch

Best Practices for Growing Cannabis with LED Grow Lights

I am a big fan of LED grow lights and have been using them for the past 10 years. Before, the only real option for growing indoor cannabis and achieving good yields of dank frosty buds was to use HID lights.

LED grow lights are a real game changer and allow you to produce high levels of PAR, the optimal spectrum for growing amazing buds and use far less electricity than HID. Below, I explain the best practices for growing with LED light, why full-spectrum LED lights are a wise investment, and my top tips to consider.

Why Full-Spectrum LED Cannabis Grow Lights Are Ideal for Beginners

In the old days, you actually needed to buy a metal halide light for the vegetative stage, then switch to a high-pressure sodium bulb for flowering. You could always combine the two lights to create a full-spectrum light.

However, with the advancement of LED grow lights, a beginner can now use a full-spectrum LED that supports vegetative and flowering development. This means you have one light from the seedling stage through harvest and can run much cooler temperatures than with HID lights.

How Much Do Indoor Grow Lights for Cannabis Cost to Run

Grow lights can range in power consumption from 250 to 1000 W. If you want a cheaper, cost-effective option, LED grow lights will definitely keep your energy bills lower and your jars filled with phenomenal buds!

Final Tips for Choosing the Best Lights to Grow Cannabis Indoors

Your LED grow light will be the most expensive piece of equipment you will need for your indoor grow room. Before making your final decision, check out my top tips!

Tip #1 – Only Use Well-Known Reputable Cannabis Industry Brands

LED grow lights took over the cannabis industry in a big way and continue to develop and produce the most energy and PAR efficient lights you can get your hands on. In recent years, LEDs have become more popular than ever, so my tip here is to only use well known brands that have a strong reputation for developing an excellent product.

Tip #2 – Check the PAR and µmol/m²/s Rating of the Grow Light

There was once a time almost 15 years ago, when you would buy a bulb based on the output of lumens. The greater the lumens meant the greater the intensity, however nowadays, PAR and µmol/m²/s are the only values that matter. If the company does not display these figures, then avoid the grow light.

Tip #3 – Dimmable LED Grow Lights Are Energy Efficient

Dimmable LED grow lights allow a grower to decide how much PAR their plants receive, during the different growth stages. LED grow lights are extremely efficient and due to the low heat output, you have more opportunity to keep your lights much closer to the canopy.

Why Autoflowers Benefit From LED Grow Lights

Autoflowering cannabis plants are known for their fast growth, compact size and short lifecycle. Because most autoflowers complete their entire life cycle in as little as 8–12 weeks, providing consistent light intensity from day one is essential.

Modern full-spectrum LED grow lights are particularly well suited to autoflower cultivation because they produce less heat and can be positioned closer to the canopy. This is especially beneficial for growers working in small grow tents where temperature management and vertical space are limited.

Another advantage of LED lighting is the ability to adjust intensity as plants mature. Young autoflowers can be sensitive to excessive light during early growth, whilst mature plants often benefit from increased intensity once flowering begins.

For growers looking for a simple indoor setup, combining quality LED lighting with autoflower seeds for beginners can help maximise growth while keeping energy costs low.

Key Benefits of LED Grow Lights for Autoflowers

Benefit	Why It Matters for Autoflowers
Lower Heat Output	Reduces the risk of heat stress in small grow spaces.
Energy Efficiency	Keeps electricity costs lower throughout the grow cycle.
Adjustable Intensity	Allows growers to increase light levels as plants mature.
Full-Spectrum Lighting	Supports healthy growth from seedling to harvest.
Better Canopy Coverage	Helps lower branches receive adequate light.
Longer Lifespan	Requires less frequent replacement compared to older lighting technologies.

Why LED Lights Work Well for Compact Autoflower Plants

Many autoflower varieties naturally remain shorter than photoperiod strains. A quality LED fixture with even light distribution helps ensure lower branches receive sufficient light, resulting in more uniform growth and better bud development across the entire canopy.

This becomes particularly important when growing indica autoflower strains, which often develop dense foliage and bushy structures that benefit from strong canopy penetration.

Autoflower Characteristics That Pair Well With LED Lighting

Autoflower Trait	LED Lighting Advantage
Compact Growth	LEDs can be positioned closer to the canopy without excessive heat.
Fast Lifecycle	Consistent light intensity supports rapid development.
Small Indoor Footprint	Efficient coverage works well in grow tents and limited spaces.
Dense Canopy Structure	Improved light penetration helps reach lower bud sites.
High-Efficiency Growing	Lower power consumption reduces operating costs.

Common Autoflower Lighting Mistakes

When growing autoflowers indoors, avoid the following mistakes:

Mistake	Potential Impact
Increasing light intensity too quickly after germination	Seedling stress and slowed growth.
Allowing excessive stretching during early growth	Weak stems and reduced canopy efficiency.
Using low-quality lights with poor canopy coverage	Uneven growth and lower yields.
Creating hot spots directly beneath the fixture	Light stress and leaf damage.
Ignoring temperature and airflow	Increased risk of heat stress and poor plant health.

A balanced environment, combined with a high-quality LED grow light, gives autoflowering plants the best opportunity to achieve their full genetic potential.

Frequently Asked Questions About Cannabis Grow Lights

What is the best grow light for cannabis beginners?

Full-spectrum LED grow lights are the best choice for beginners. They are energy-efficient, produce less heat than HID lights, and provide the complete light spectrum cannabis plants need from seedling through harvest.

How many hours of light do cannabis plants need each day?

Cannabis plants require 18 hours of light and 6 hours of darkness during the seedling and vegetative stages. To trigger flowering, indoor growers should switch to a 12-hour light and 12-hour dark cycle.

How far should LED grow lights be from cannabis plants?

The ideal distance depends on the plant’s growth stage and the power of the light. Seedlings should be kept 12-18 inches from the light source, while vegetative and flowering plants typically perform best with LED grow lights positioned 18-24 inches above the canopy.

Can cannabis plants get too much light?

Yes. Excessive light intensity or hanging grow lights too close to the canopy can cause light stress and light burn. Common symptoms include bleached white tops, yellowing leaves, taco-shaped foliage, and reduced yields.

What PPFD level is best for cannabis flowering?

Flowering cannabis plants generally perform best at PPFD levels between 600 and 1050 µmol/m²/s. Higher light levels promote larger yields and denser buds when environmental conditions and nutrition are properly managed.

Are LED grow lights better than HPS lights for cannabis?

Modern LED grow lights are often considered superior to HPS lights because they produce less heat, use less electricity, offer full-spectrum lighting, and provide excellent PAR output. However, HPS lights can still produce high yields when used correctly.

Can I use regular LED lights to grow cannabis?

Regular household LED bulbs can support seedlings and young plants but typically do not provide enough PAR output or light intensity to grow cannabis successfully through the flowering stage. Dedicated cannabis grow lights are recommended for best results.

What colour light is best for cannabis plants?

Blue light (400-500nm) is most beneficial during vegetative growth because it promotes compact growth and strong branching. Red light (600-700nm) is essential during flowering because it encourages bud development and flower production.

How much electricity do cannabis grow lights use?

Cannabis grow lights vary widely in power consumption. Small LED grow lights may use as little as 100-200 watts, while larger systems can consume 600-1000 watts or more. LED lights are generally the most energy-efficient option for indoor growers.

What size LED grow light do I need for a grow tent?

The required grow light size depends on the dimensions of your grow tent. A 2×2 tent typically requires 100-200W of LED power, a 3×3 tent requires 300-450W, and a 4×4 tent generally performs best with 480-650W of quality LED lighting.