The Budding Botanist: can you grow cannabis with any light?

cannabis lights

With more states legalizing cannabis, interest in cultivating the plant continues to rise. And while cannabis may grow like a weed, it takes time, care, and consideration to craft top-shelf buds.

GreenState knows that people have lots of questions about growing cannabis. To help take the guesswork out, professional cultivator Kurt Kinneman, owner of Kinnektion Farms and horticultural engineer at AI Grow, is here to answer your budding queries. From seed to smoke, GreenState has you covered.

RELATED: The Budding Botanist: what do you need to grow cannabis?

Question: can you grow cannabis with any light?

Technically, yes. When I began my growing adventure, I packed as many standard 60-watt CFL bulbs as possible into a 4′ x 4′ x 4’ space. The plants grew, but the finished product was much more leafy and less dense than I was used to seeing in the bud I was buying. 

As my knowledge of growing progressed, I learned that not all light is created equal. Research and development for indoor agriculture have revealed a lot about the ideal lighting environment for cannabis. Here’s what we know.

A full spectrum

Firstly, light is a spectrum. There is a small portion of this spectrum that includes visible light, which is light that includes all the colors that we think of when we picture a rainbow. 

When looking at lights, you will see that some LED lights will list the diode color as a number, and that number will have the unit nanometer attached to it.  The amount of nanometers refers to the color on the visible spectrum. The visible spectrum range runs from around 400 nm, purple right next to UV light, to 800 nm, a red light that borders on infrared light. 

Another way the color of the light can be expressed is in degrees Kelvin. This color spectrum goes from around 2000k to 7000k, where 2000k refers to more red light, and 7000k refers to more blue light. This scale refers to any standard bulb, high-pressure sodium (HPS), or metal halide (MH) bulb. HPS bulbs fall around the 2200k spectrum, far leaning red, while MH bulbs have a color temperature of around 6500k.

When deciding on a grow light, it is important to understand that plants like different light spectrums at various stages of growth. Think of how a plant grows outdoors: in the spring and early summer, the plants receive intense sunlight as the sun rises higher on the horizon. When we get to the summer solstice, the sun starts to sink into the sky, and the intensity decreases. We can see this when we think of a bright sunny day in the middle of summer compared to the dimmer fall light. 

This directly translates to a bluer spectrum of light during the summer months and a redder light as we enter the fall season. So, when you are growing plants in a vegetative state, they prefer a blue light in the 400 nm range, or 6500k range, and when you switch to flower, the plants like a redder light in the 800 nm or 2500k range.

cannabis plants under light
Flowering cannabis plants under LED lights. Photo: Cappi Thompson / Getty

Light intensity matters

Besides the spectrum of light, there is also light intensity. The light intensity can be measured in lumens or photosynthetic active radiation (PAR). 

Lumen is a measurement of the brightness of light perceivable by the human eye and measured in foot candles or LUX. PAR is a measurement of light energy perceivable by a plant for photosynthesis and is more commonly used by growers to describe the intensity of light the plants are receiving. 

Another light intensity measurement commonly used by growers is photosynthetic photon flux density (PPFD). This measurement is expressed with the units of micromoles per square meter per second and is a measurement of how much PAR is actually reaching the plant surface. 

For the average person, this is like trying to understand a foreign language. Luckily, there are ways to determine exactly what light intensity you need for your space. All reputable light manufacturers can provide you with a PPFD map for their lights. This map will show you where the PPFD is most intense and how it varies within the footprint of the light at different distances from the leaf surface. 

Simply determine the square footage of your grow and then check the PPFD map. Typically, you will need less intense light in the veg stage and more during flower.

The power play

The final factor when looking at grow lights is how much power they use. Every fixture has a different wattage that it uses to either power the bulb or the diodes. Typically, a light rated at 1000 watts will be sufficient for a 5’ x 5’ space, a 600-watt light is good for a 4’ x 4’ space, and a 250-watt light is good for a 3 ’x 3’ space. 

When considering what wattage you should choose for your space, you should also be mindful of how much of a draw these wattages will have on your electrical system. A 1000-watt light will draw around nine amps of power, so it is important to make sure you have the proper wiring in place to run your lights and also to make sure you aren’t using too much of an electric load for your main breaker panel. Of course, the more power you draw, the higher your utility bill will also be.

Choosing your lights

For the budding botanist, picking a grow light can seem daunting. People with one small space or tent will want a light that works well in all stages of the plant life cycle. Ideally, this would be a full-spectrum LED that has adjustable light intensity and spectrum. These lights require a bigger upfront investment but provide cost savings over time since they’re more energy-efficient than other types of lights.

HPS lights were more common in grows back in the day. They offer a specific spectrum and intensity ideal for the plant’s life cycle; HPS lights are less expensive but use more power overall.

New growers can expect to pay around $1000 for a good LED light. I personally like the Grandmaster, GE Arize, and Foshe brands. Budget-friendly options include the AC Inifity, ViVo Sun, and Spider Farmer lines.

Don’t want to break the bank? Search online for used lights—someone may be upgrading their system, giving you the perfect opportunity to get a tried and true lamp before graduating to something more sophisticated. 

The bottom line is your bud will only be as good as the inputs you use—aka the light, nutrients, and growing medium. Cheaper lights will get the job done, but if you want a top-shelf smoke, it may be worth investing a bit more in your equipment. 

This article was submitted by a guest contributor to GreenState. The author is solely responsible for the content.

Kurt Kinneman is a cannabis cultivator and owner of Kinnektion Farms. He is also a horticultural engineer at AI Grow, a provider of automation solutions for controlled environment agriculture. In addition to cannabis, Kurt also grows pumpkins on his family farm.