How to choose the best indoor marijuana grow light

Written by Pat Goggins

One of the crucial elements a cannabis plant needs is light. During photosynthesis, a plant converts light energy into chemical energy, allowing it to grow strong and healthy, and with cannabis in particular, light also fuels bud production. 

When growing outdoors you can harness the power of the sun, but in an indoor environment, sunlight is mimicked through the use of grow light bulbs, which aim to display the same spectrum of light as the sun.

Grow lights allow you to control exactly how much light your plants receive, ensuring they get the same amount of light day after day, without the grower having to solve problems with bad weather or cloudy days that happen in an outdoor environment.

Some grow lights are more expensive than others, but also more efficient, saving money in the long run. Some lights are bulky with many parts, some light in weight, and some are better suited for young or mature plants.

There are many different kinds of lights out there, so it can be daunting to know where to begin. Here’s a guide to four basic types of grow lights on the market and the pros and cons of each. 

Factors to consider before buying a grow light

How much does a grow light cost?

The first thing to consider before buying a grow light is how much money you want to spend. With more states coming online with adult-use legalization, homegrowing is becoming more popular and growing technology is getting better and more efficient all the time. 

You can find lights for under $100, but they may be low quality and not produce the right spectrum of light, and you can also easily spend as much as $2,000 for a large, state-of-the-art LED. 

Consider how often you’ll be growing weed and how long it will take to pay off the initial investment—if you grow once a year, it’ll take a lot longer to pay off an expensive light than if you grow multiple harvests a year. 

Aside from the price of the actual light, also take into account utilities—all lights will add to your electricity bill every month, but some more than others. High-intensity discharge lights—known as “HIDs”—may be cheaper to buy but can gobble up electricity, whereas LEDs are more efficient and kinder on your electricity bill but usually more expensive to buy. 

Another consideration with cost is that some lights run hotter than others—HIDs, for example—so they may require additional fans or an AC unit to cool down a grow space. Extra equipment means more electricity, also driving up your utility bill.  

How many grow lights do I need to grow weed?

The typical homegrower will only need one or two lights. Most states limit grow amounts to 6 or 12 plants, and one or two lights should be plenty for that. If you plan on running two separate rooms, one for vegetative plants and one for flowering plants, you’ll need two lights. 

How big a light you need will depend on the number of plants you plan on growing, but also on the size of your space. If you’re growing in a closet or a small grow tent, you’ll only be able to fit one small light in there. If you have a wide open basement, you could invest in a bigger light as opposed to two smaller ones. 

Power equals poundage, so if you want big yields you’ll need more wattage. Professional LEDs can start at as little as 200 watts, and go up from there. A high-watt light can double the work of several low-watt bulbs.

Other considerations when choosing a cannabis grow light

Ventilation

Ventilation is also a concern. If you’re growing in a tight space with a light that runs hot, you’ll need to have fans in there, which also take up space. If there’s not enough room for a light and a fan, you may need to invest in a light that doesn’t run as hot, such as an LED. For example, grow tents are usually built tall to allow room for equipment up top, not to grow plants all the way to the ceiling. 

Plant stage

Young and mature plants, or vegetative and flowering plants, respectively, like different types of light, and you can buy grow lights that target each spectrum. Commonly, growers using HIDs will use MH bulbs for vegetative plants and HPS bulbs for flowering. Some LEDs are also designed to target different light spectra. 

Safety

Make sure you have enough outlets and power available in your breaker board for your grow space to comfortably accommodate all equipment. Figure out all pieces of equipment, such as lights, fans, possibly an AC or dehumidifier, and calculate how much power they’ll require. You’ll be running this equipment every day for months, so if you don’t have enough power it can be dangerous. Never overload an electrical outlet.

Types of marijuana grow lights

There are many types of lights, but below are the four most common you’ll find in a grow room. There are many variations within each of these four types as well, and new lights and technology come out all the time. 

Lights have fixtures and bulbs, and some require a ballast. Depending on the type and model, the bulbs or the fixtures can be more expensive. There are a lot of abbreviations, but don’t be alarmed. 

HID lights for growing marijuana

HID (high-intensity discharge) is an umbrella term under which MH and HPS bulbs fall, which we’ll discuss more below. These types of lamps have a hood that reflects light and bulbs that are enclosed capsules containing a gas, as opposed to bulbs you’d find in your house, which have a filament that heats up. 

For HIDs, light occurs as an arc between two nodes inside the bulb. The gas contained in these bulbs is what makes MHs and HPSs different. HID bulbs are usually more expensive than the reflective hoods that hold them.

HIDs have been the standard in indoor weed growing for decades, but LEDs are quickly catching up to them.

Both types of HIDs are usually inexpensive to buy but will eat up electricity. HIDs throw off a lot of light and heat, which the plants need to bulk up and get potent. But, they run hot, contain heavy metals, and ballasts can fail.

However, because of their low price, if you’re new to indoor growing and not sure how often you’ll do it, you may want to invest in an inexpensive HID light at first to test the water.

You can find HID reflector hoods, as well as MH and HPS bulbs at any local grow shop.

MH (Metal halide)

These bulbs contain mercury and metal halides, produce a blueish light, and are commonly used for vegetative growth. They require a ballast to regulate the current. In the past, ballasts have been big and bulky, but digital ones are now available. 

HPS (High-pressure sodium)

These HID bulbs usually contain sodium, mercury, and xenon, and produce a yellow/orange light, and are commonly used for flowering plants. Some growers will start plants under MH bulbs and switch them to HPSs when plants go into the flowering stage, using the same hood. These lights also require a ballast.

Best HID grow light brands

Here are a few different HID grow lights at different price points.

• Hydro Planet 150W: $191
• Yield Lab 400W: $144
• Vivosun 600W: $139

CFL lights for growing weed

CFLs (compact fluorescent lamps) are fluorescent lights similar to what you’d find in a school or office building, but smaller. For growing weed, they are usually called “T5s”—the “T” stands for “tubular” and the “5” refers to its diameter, “⅝”. 

There are daylight bulbs and warm white bulbs; the former better for vegetative growth, and the latter for flowering. 

These fluorescent lights are cheap and efficient and great for vegetative growth. They’re especially great for helping along germinating seeds and small seedlings because they don’t put off much heat and won’t scorch the delicate seeds. They won’t run up your electricity bill too much.

The downside to CFLs is they aren’t great for flowering plants, and growers will usually use another type of light to finish plants. CFLs just don’t generate enough intense light for plants to pack on weight.

Fixtures come in all shapes and sizes and can usually accommodate 4-12 long fluorescent bulbs; a standard size is 8 bulbs. Fixtures usually have a reflective material to bounce light in one direction, down on your plants. 

As with HIDs, you can find CFLs at any local grow shop.

Best CFL grow light brands

Here are a few different CFL grow lights at different price points.

• Hydro Planet T5: $170
• Vivosun T5: $179
• Hydrofarm T5: $96

LED lights for marijuana grows

LEDs (light emitting diodes) are relatively new to the cannabis growing world, compared to HPSs, MHs, and CFLs, but they are quickly proving to be the way of the future. LEDs may be more expensive to buy initially, but they are far more efficient and kinder to the environment and your electricity bill. Some cities even give tax breaks to commercial growers who install or switch to LEDs because they’re better for the environment.

LEDs also typically run a lot cooler than HIDs, so you may not need extra equipment to cool down your grow space, and one LED can usually be used for both vegetative and flowering growth. Some high-end LEDs allow you to change the spectrum for each growth stage.

New LED grow lights come out all the time, but knockoffs abound. There are a lot of cheap LEDs that don’t produce the right spectrum of light for plants. 

Because LEDs are efficient in the long run, there are a lot of new companies competing. A great LED to get started with is Black Dog LED’s PhytoMAX-2 series: They use a light spectrum suited for plants in both vegetative and flower growth, and their UV output is great for high trichome production and large yields. The lights also come in different sizes to accommodate different grow spaces. 

Best LED grow light brands

Here are a few different LED grow lights at different price points.

• Covert 250W: $349
• Grower’s choice 420W: $450
• Black Dog PhytoMAX-2 125W: $469
• Gavita RS1900 E 650W: $799

Ready to start growing your own marijuana?

Buy marijuana seeds on Leafly.