Grow lights are an indispensable part of indoor growing. Without light, there can be no photosynthesis, and cannabis plants won’t be able to survive.
For some med patients, growing at home is essential for obtaining a reliable supply of medicinal cannabis. At-home grows can not only save patients time and money, but it gives them access to the exact strains they want all year long.
In this article, we discuss everything you need to know about cannabis grow lights, from the different options available to their effect on growth, yield, and quality.
The 3 Types of Cannabis Grow Lights
If you’re growing your plants outdoors, the natural light from the sun is all you'll need to produce significant yields. But to extend the growing season year long (and to avoid other challenges that come with outdoor cultivation), you’ll need to move your plants indoors. And that means finding the right cannabis grow lights.
Grow lights feed your plants by mimicking the same light spectrum as the sun. Of course, choosing the right lights isn’t quite so simple. Some lights are cheaper or more expensive than others. Some require more energy or are more efficient for different plants or cultivation setups.
If you're new to indoor cannabis cultivation, you may be feeling overwhelmed by the selection of grow lights (and the relatively technical terminology that comes with them).
But, not to worry!
Let’s clear things up and help you get your home grow started, starting with the most common types of grow lights:
- Traditional CFL (Compact Fluorescent Lamps)
- HID (High-Intensity Discharge)
- LED (Light Emitting Diodes)
Traditional Compact Fluorescent Lamps (CFL)
When it comes to weed grow lights, CFLs are the most traditional choice. These were the lights of choice for many indoor cannabis cultivators in years past.
CFLs have long been the light of choice for many farmers and horticulturists (usually in colder climates) to grow various plants indoors outside the growing season. Naturally, early cannabis cultivators followed suit.
Compact fluorescent lamps are often used for temperature-sensitive cannabis plants, such as seedlings and clones. And improvements over the years have made CFLs more effective and efficient than ever.
But despite their long history and widespread use, compact fluorescent lamps aren’t for everyone.
- CFLs can be expensive, especially when compared to more modern lighting options that are available.
- You'll need quite a few CFLs to capture the full spectrum of light required for your plants.
High-Intensity Discharge (HID)
High-intensity discharge grow lights, or HIDs, were initially developed to light large indoor public spaces, such as stadiums, concert halls, and arenas.
However, horticulturists soon discovered they are very effective for growing plants like marijuana. In fact, HIDs have become the go-to choice for indoor cannabis cultivation for many cultivators. This is because they are relatively inexpensive while providing the significant amounts of light and heat necessary for bigger cannabis yields.
There are two types of lightbulbs for HIDs used for weed grow lights:
- Metal Halide bulbs,
- and High-Pressure Sodium bulbs.
You should be able to find everything you need to get started with HIDs at your local grow shop.
Metal Halide
As the name suggests, metal halide bulbs are manufactured with metal halides and mercury. They produce a blueish-white light and are best for cannabis plants in their veg phase.
High-Pressure Sodium
High-Pressure Sodium bulbs, or HPS bulbs, contain sodium, xenon, and mercury. This results in a yellow or orange light, compared to the blue of metal halide bulbs.
This light spectrum produced by HPS bulbs are considered best for the flowering phase of cannabis growth. As such, many cannabis cultivators that use HIDs will have both metal halide and HPS bulbs used for their respective growth stages.
Although HIDs have been the standard type of marijuana grow light for many years, they have drawbacks.
- HIDs have a tendency to be incredibly hot,
- they require a lot of energy (which can mean high electricity bills),
- and HIDs contain heavy metals, which may be a deal breaker for some cultivators and DIY home growers.
This brings us to the last type of weed grow light we'll cover: LEDs.
Light Emitting Diodes (LED)
Light Emitting Diodes, or LEDs, are a relatively new lighting option gaining popularity among indoor growers.
There are three main types of LED grow lights for cultivating cannabis:
- Traditional: contain compact diodes and lamps with low-medium wattage. Most LED marijuana grow lights are manufactured in this way.
- Spread Style: consists of smaller LEDs spread over a large surface area.
- Chip-on-Board: are the largest and most powerful type of LED grow light. They offer the brightest and most intense LED lighting.
LEDs can be more expensive than HIDs, but make up for the entry cost with their incredible energy efficiency. Not only will you save on your monthly electricity bill, but you’ll be helping the environment, too.
Another benefit of using LEDs as your weed grow lights is that they don't get as hot as HIDs. So while the initial cost of LEDs is higher, HID growers often need to purchase extra equipment to keep their grow space from getting too hot. Not to mention that super-hot HID lights can be a fire hazard if not properly ventilated.
LED lights can also simplify your work as a home grower, as they can be used for both veg and flowering stages.
Before rushing out to purchase LED lights, though, remember that not all lights are designed for indoor cannabis grows. Be sure to check the following before ordering your lights (and keep reading for a list of our favorite grow lights):
- Is the grow light rated highly for reliability?
- Does it produce the proper light spectrum for cannabis?
- Is it meant for indoor plant cultivation?
Lighting for Cannabis: Factors that Affect Growth
There are several lighting factors that determine how well your indoor weed plants will grow.
1. The Light Spectrum
The most significant factor that affects plant growth is the light spectrum produced by your cannabis grow lights. Depending on your choice of lights, the light spectrum can vary tremendously.
While the sun naturally provides the full spectrum of light that marijuana plants need to thrive, you'll need to be more strategic with grow lights. Even subtle differences in the light spectrum in your grow can have significant effects on your final product.
Which brings us to our next point…
2. PAR (Photosynthetically Active Radiation)
Photosynthetically active radiation, or PAR, is the part of the light spectrum that a plant needs to undergo photosynthesis. For cannabis, PAR is between the blue/violent low end of the spectrum and the orange/red high end.
How can you put PAR to use in your grow?
Cannabis plants require different spectrums of light depending on their growth stage.
- During the veg phase, cannabis plants need plenty of low-end blue light, which translates to PAR values in the 400-500 nm (nanometer light) range.
- While a marijuana plant is flowering, it will need high-end orange/red light, or PAR values above 600 nm.
While this may sound complicated, you can pick up a PAR meter to ensure your plants receive the proper spectrums of light at the correct times.
3. Light Intensity
Light intensity, measured in lumens, also plays a significant role in the size and strength of your harvests. Generally speaking, the more light provided to your plants, the better.
If you buy lights specifically designed to grow cannabis – and if you have enough (and the right set-up) – they should provide enough light intensity for healthy growth.
If your grow lights aren't intense enough, or if they’re placed too far away from your plants, the growth cycle will suffer. The ideal distance ultimately depends on the strength of the grow lights. We provide a table at the end of this article to help you plan your space.
4. Photoperiod
Finally, the photoperiod, or the time of day a plant receives light, will play a role in your marijuana harvests.
In a nutshell, lengthening or shortening your plants' photoperiod (a concept light deprivation growers are familiar with) will significantly affect how long the plant stays in the vegetative phase and when it begins to flower.
Generally speaking, a cannabis plant will kick off the flowering stage if the photoperiods are shorter (approximately 12 hours per day). On the flip side, flowering will be delayed when photoperiods are longer (approximately 18 hours per day).
Achieving the right photoperiod for an indoor grow is as easy as turning your grow lights on or off as necessary (and a timer makes this even easier).
Recommended Cannabis Grow Lights
Best CFL Lights For Growing Cannabis
Hydroplanet T5
Hydrofarm Agrobrite FLCDG125D
DuroLuxT5 Grow Light
Best HID Lights For Growing Cannabis
Sun System LEC 315
Sun System HPS 150W Fixture with Ultra Sun Lamp
gGRO™ 630W Ceramic Metal Halide
Best LEDs Lights for Growing Weed
Spider Farmer SF1000
MARS HYDRO TS-1000
Phlizon COB Series 2000W LED
Practical Tips for Grow Lights
✔ Mimic the Light Deprivation Method
While 'light depping' typically refers to outdoor grows deliberately limiting the amount of sunlight per day their plants receive, indoor growers can do the same with greater ease.
Instead of covering your plants or greenhouse with a tarp, you can just turn your lights off at specific intervals to achieve the same effect.
Doing so will cause your plants to begin flowering much quicker, which could translate to better and more frequent harvests throughout the year.
✔ Use The Right Amount of Light For Your Plants
If you want to get big, healthy yields, you'll need to use the right number of lights for the plants you're cultivating.
If you're using too few for your grow, the plants won't receive the proper light intensity, and their growth will suffer.
Generally speaking, your grow lights should produce 400-600W per m².
✔ Distance Your Lights Correctly
If you have the right number of lights but distance them too far (or too close), they'll do you no good.
Ultimately, the distance you hang your lights will depend on the wattage and the type of light you purchase. You can find a distance chart at the bottom of this article.
✔ Change Lights at the Proper Times
To get the most out of your grow, and depending on the grow lights you use, you may need to change lights during the various stages of your plants' growth.
Different growth phases require different light spectrums to thrive. For example, if you're using HIDs, metal halide bulbs (which produce a bluish light) should be used while the cannabis plant is in veg. However, during the flowering stage, these bulbs should be switched to HPS (which produces orangish-red light).
HID Grow Light Distance Chart
| Strength | 150W | 250W | 400W | 600W |
| Distance | 8 - 12 in | 10 - 14 in | 12 - 19 in | 14 - 25 in |
LED Grow Light Distance Chart
| Strength | 200W | 400W | 600W | 800W |
| Distance | 10 - 16 in | 15 - 20 in | 18 - 32 in | 20 - 35 in |
The information in this article and any included images or charts are for educational purposes only. This information is neither a substitute for, nor does it replace, professional legal advice or medical advice, diagnosis, or treatment. If you have any concerns or questions about laws, regulations, or your health, you should always consult with an attorney, physician or other licensed professional.
