Marijuana 101: Grow Lights


Fluorescent-grow-lightsSo, you’re thinking about growing marijuana and need to know more about grow lights? Whether you’re doing it legally in Colorado or performing a stealth operation in another state, the characteristics of your grow light will have a dramatic effect on the yield of your crops. The type of light also plays a role in your electricity costs. It’s important to understand exactly what to expect with each type of cannabis grow light available, so let’s take a look at some of the key factors that will help you decide which light to buy:

HID (High-Intensity Discharge) lights are the standard for cannabis growing. The most common HID lights for indoor grows are Metal Halide (MH) and High-Pressure Sodium (HPS). HID lights require more electricity and a larger upfront investment than other lighting alternatives, but they can also be considerably more powerful. If you choose an MH or HPS grow light, it’s important to have a high-functioning exhaust system due to the strong aroma of cannabis that will be coming from your grow room. HID lights also give off a lot of excess heat, and an effective exhaust system will help manage this issue.

High-Intensity Discharge

At different phases of the cannabis plant’s life cycle, different HID lights are recommended for the best results. Metal Halide lamps create a blue light that is well-suited for plants in the vegetation stage (this is the time when the plants begin to grow branches and leaves, still in the earlier part of the growing cycle). High-Pressure Sodium lights produce an orange/red light that helps stimulate the plant’s growth hormones during the flowering stage, which mimics autumn for an outdoor grow. HPS lights use high levels of energy but can make a strong impact on the yield during the flowering stage, so it is worthwhile to consider them. Some growers choose Ceramic Metal Halide (CMH) lights, which are in between MH and HPS lights regarding efficiency.

If you choose to go the HID route, you’ll need a ballast to plug it into the wall. You’ll also want to purchase a hood to reflect the light coming from your bulbs. Make sure to match the bulb wattage with the wattage of the lamp (a 600W HID lamp should only use 600W bulbs, etc.).


Fluorescent lights are the second option. They come in two varieties: CFLs (compact fluorescent lights) and T5 lights. Both are less expensive and more energy efficient than HID lights, and they emit a wide spectrum of light, which is beneficial to the plants. In many cases, growers use fluorescent lights in conjunction with MH or HPS lamps to have a high-powered system that also exposes plants to a wide spectrum of light. Growing cannabis with only fluorescent lights is possible, but the yield will likely be smaller because the lights aren’t as powerful as a typical HID.


A third option and one that is gaining traction in the cannabis industry is LED grow lights. LEDs are smaller and give off less heat than HPS lights, and they can increase yield with better energy efficiency. Because LEDs use less electricity than HPS and MH lights, they are becoming a popular alternative to the standard HID. Environmentally conscious growers also choose LEDs because they don’t contain mercury like HIDs. LEDs also don’t burn the plants like HIDs do when they are placed too close.

LED lights are more expensive than HIDs and require a larger upfront payment, but over a longer period of time, they will bring a higher return on investment due to the lower energy costs. In addition to the cost of keeping HID lamps on, growers will incur significant expenses on fans and exhaust to reduce the level of heat in the grow room. HPS and MH lights also require light bulbs to be changed more often than LED lights, another cost to consider.

Wattage Specs

When purchasing a lighting setup, make sure that the wattage of the bulbs is suitable for your room and your expected yield. Commercial growers tend to use bulbs with higher power than home growers because they need to produce higher yields. For a home grower, a single 1,000W light could be enough for six to eight plants, but purchasing a 400W and 600W lamp and spacing them out in the grow room could spread the light around for a better overall yield. Whether the plant is a sativa, indica, or hybrid can also play a role in the amount of wattage needed. Sativa plants use around 66 watts of light per square foot, while indicas use between 40 and 45 watts (hybrids fall in between at about 60 watts).

grow light with hpsIn general terms, more light produces more cannabis, but there’s no need to use too much power and run up the electricity bill. Whereas a commercial grower might have 20 or more 1,000W grow lamps in a room, combined with some additional fluorescent lights to give the plants a greater spectrum of light, a home grower could use just a single 400W or 600W light if they’re only trying to produce two plants in a small closet. For example, a 2′ x 2′ grow room would do fine with a 250W HID, but if the plants are spread over a 5′ x 5′ area, then a 1,000W lamp might do better.

If you’re choosing between a HID and an LED lamp, some pretty straightforward calculations can aid the decision-making process. As previously stated, LED lights are typically more expensive than HIDs, but they have lower monthly costs, which will offset the higher price tag. Spending $969 on a top-notch 600W LED light is a higher upfront investment than spending $300 to $500 on a 600W HPS, but the monthly electricity cost of using an HPS will be higher (also don’t forget you’ll need more fans and a more efficient exhaust system with HPS lights). During the vegetative stage, lamps will be on for 18 hours per day, and during flowering, they’ll be on for 12 hours per day. That’s a large electricity expense, and it’s worth crunching some numbers to see whether it is worth it to make the higher initial investment in an LED.

Be Discreet

It should also be pointed out that if you’re in a state where it’s illegal to grow cannabis, HID lights could potentially make the electric bill jump to the point where it would look suspicious to authorities. HPS lights might also be detectable by thermal imaging techniques used to find infrared heat, where LED lights don’t put out enough heat to be spotted. Having a smaller grow operation is one way to prevent any chance of getting “busted,” so keep all of these factors in mind if you’re in the market for a new lamp.

It’s quite easy to purchase grow lights on the internet. Since they are used for horticultural purposes beyond just cannabis growth, there are no laws against purchasing grow lights like there are with buying marijuana. A quick Amazon search for “cannabis grow light” will send you on your way to finding the lamp that’s right for you. There’s also this list of the best 10 LED grow lights. If you are in a state where cannabis is legal, it couldn’t hurt to stop in a local dispensary and ask the budtenders for some additional thoughts on which brands they prefer. The cannabis industry has a “help each other out” kind of vibe, so don’t hesitate to ask the experts their opinions. Good luck!