Cannabis Cultivation Lighting 101: Creating Sunshine Indoors

Lighting is one of, if not the most essential ingredient needed for a quick, high-yielding crop. Your lights may very well be your single greatest expense, but very well worth the investment. Maximizing light distribution to your plants will enhance photosynthesis tremendously.

Photosynthesis is the process by which carbon dioxide and water are turned into sugary plant food and oxygen. This works the same for your common houseplant as it does for your favorite strain of sticky icky. Regardless of plant type, the effect is similar; the more light your plants receive, the faster and bigger they will grow.

Understanding How Grow Lights Work

Light is made of photons, which are tiny particles that inexorably travel at the speed of light. Photons in light beams vibrate with different frequencies and wavelengths. Humans can see photonic radiations within wavelengths from 380–680nm, while plants’ sensitivity to light ranges from 200–800nm.

Not all wavelengths within this spectrum produce the same effects on photosynthesis; those that most activate biochemical processes in plants are called PAR (photosynthetically active radiation), which has a spectral range of 400–700nm.

Light can be measured in photometric quantities derived from the human eye’s sensitivity to color, or else with radiometric quantities related to the energy transported by light beams. Lumens and lux are commonly used photometric units that refer to light perceived by the human eye.

However, photometric measurements do not indicate how much light energy a lamp sends to a plant for photosynthesis because they don’t include the PAR variables. Despite that, lumens and lux can provide an initial indication of a specific bulb’s output, and we can compare different products by measuring their photometric efficiency with the lumen: watt ratio, regardless of the eventual differences in light spectrum output at different wavelengths.

Lux and lumens work well in measuring MH, HPS, CFL, and T5 lights, but they won’t accurately measure the efficiency of an LED light when growing cannabis.

How Kelvin Degrees Impact Light Warmth

The formula between Kevin and nanometers; 2,897,768 / K = nanometers (nm) however the two do not relate perfectly and this can only be used as a guide as to where a light source might be peaking in a precise nanometer (nm). Remember each light source will offer a spectrum measured in nanometers (nm), say 400 to 700 nm.

The lower the degree K, the more “warm”, or red the light appears. The higher the degree K, the bluer, or “cooler” the lamp appears. Kelvin is a scientific term that measures the color of a light source relative to a black background. In simpler terms, it is the average degree of warmth or coolness of a light source, not with regards to the physical temperature, rather to the visual temperature of the light.

Kelvin and warmth chart

Depending on which metal halide (MH) grow light you use they have an average of 3,200 to 5,500K while high-pressure sodium (HPS) grow lights have an average of 2,200K and full-spectrum LEDs use several different LEDs in a mix which cover the blues, reds and also whites and far-red. You often see LEDs that just look like a mix of blue and red light these can work for the vegetation side of growing but the better versions look like ‘white’ light and emulate the sun very well.

Lamp Types Dictated By Light Color & Intensity

Metal Halide (MH) lamps normally produce a high proportion of light in the blue wavelength, so are used early in the growth cycle to promote compact, bushy plants. High-Pressure Sodium (HPS) lamps produce high proportions of light in the orange and red wavelengths but relatively small amounts in the blue range. This is why HPS lights are used to trigger bud formation and enhance flowering and fruiting.

CFL grow lights run much cooler than MH or HPS, so can be placed closer to the plants. Several manufacturers are now creating CFLs more in tune with growing plants, including producing light into the orange end of the spectrum. Some growers routinely use CFLs for all of their seed/clone/early vegetative stages of growth.

Main Classes of Cannabis Lightning Explained

There are lots of options for grow lights that work well for growing cannabis indoors but in the end, they boil down to 3 major types:

  • Fluorescent grow lights
  • Compact Fluorescent Lights (CFLs)
  • T5 grow lights (and other fluorescent tubes)
  • High-Intensity Discharge (HID) grow lights
  • Metal Halide (MH)
  • High-Pressure Sodium (HPS)
  • Ceramic Metal Halide (CMH, LEC, Light Emitting Ceramic)
  • LED grow lights
  • (LEDs come in a huge variety of sizes and form factors. There aren’t any “standard” types yet, though some lamps get better results than others.)
synthetic vs organic nutrients

Fluorescent Grow Lights: Common and Affordable

Fluorescent grow lights come in many different shapes and sizes, from twisty bulbs to long tubes. Fluorescents are popular because they make efficient and pleasant lighting for humans, and also work great for herb gardens and other types of low-key indoor gardening without using a lot of electricity.

  • Compact Fluorescent Lamps (CFL) grow lights

This type of light is perfect for starts and seedlings. They are also popular for growing low-light plants like herbs and African violets. Fluorescent lights are low intensity and need to be placed within 8” (up to 15” for shade-loving plants) of the plants to be effective. They are generally a poor light source for flowering and budding primarily because of their low lumen output.

  • T5 grow lights

T5 grow lights are one of the most easily available types of grow lights and are used to grow many different types of plants. As a result, they’re available in many garden and home improvement stores. T5s are much bigger/wider than CFLs and usually come as part of a panel, but they can still be kept mere inches away from your plants without worrying about burning them.


Cheap to buy: They don’t use a lot of electricity or make a lot of heat unless you have a lot of them packed together in a small space)

Great light spectrum for growing cannabis: Since lights can safely be kept just a few inches away from plants, they’re a good choice for short spaces)

One of the best lights for clones, seedlings, and young plants: Big lights must be kept far away from young plants to avoid burning them, which ends up wasting a lot of light and energy. By using smaller lights like fluorescents while plants are still short, you can save quite a bit of money on electricity during those first few weeks compared to using a high-powered grow light.


Fluorescent grow lights get smaller yields per watt than the other types of grow lights if you use them in the flowering stage while buds are forming. With fluorescents, you can expect about 0.25 grams of buds for every watt of electricity (using the true watts out the wall, not any type of “equivalent” watts), while LEDs and HPS get 2-4 times as much yield per watt of electricity.

The light from a fluorescent lamp doesn’t penetrate far down into the plant so they are best suited to plants that have been trained to grow short and flat; they aren’t powerful enough to support tall plants in the flowering stage.

High-Intensity Discharge (HID) Grow Lights

HID grow lights are much more efficient than fluorescent lights and are powered by large, oddly-shaped bulbs. They are usually screwed into a reflector or hood to reflect more light down onto the plants.

high intensity grow lighting

HIDs are great at growing cannabis, but they also get very hot and are usually hooked up to an exhaust to help vent out heat.

  • Metal Halide (MH) grow lights

Metal halide bulbs produce an abundance of light in the blue spectrum by an electric arc through the high-pressure gaseous mixture of metal halides (bromine and iodine) and argon, xenon, and mercury. This color light promotes plant growth and is excellent for green leafy growth and keeping plants compact. They require a ballast to regulate the current. In the past, ballasts have been big and bulky, but digital ones are now available.

  • High-Pressure Sodium (HPS) grow lights

High-pressure sodium (HPS) bulbs emit an orange-red glow and are deficient in the blue spectrum. This band of light triggers hormones in plants to increase flowering/ budding in plants. High-Pressure Sodium grow lights are often used during the flowering stage because they are very efficient and their yellow light stimulates bud production. HPS grow lights in the flowering stage get better yields per watt of electricity than any other type of grow light available today, which is a big part of why they are so popular.

  • Ceramic Metal Halide (CMH) & Light Emitting Ceramic (LEC) grow lights

CMH & LEC grow lights operate a lot like a regular metal halide (MH) grow light except instead of using quartz they use a ceramic arc tube, very similar to what’s used in HPS grow lights. This is why they’re often called “ceramic metal halides,” and they have some distinct advantages! Compared to regular MH bulbs, LEC lights give off a more natural color, produce more light per watt, and last longer.


HIDs are the most efficient type of grow light (gets the highest yields/watt).

Of all the HIDs, HPS grow lights are the most efficient and the best for the flowering stage. When using HPS grow lights in the flowering stage, you can expect about 0.5-1 gram/watt if all goes well.

HID lights are simple to use because they can be hung at the right distance from the plants with no guesswork on your part (unlike LEDs), and no need to adjust the lights all the time (like fluorescents).


HID bulbs get hot and generate a lot of heat. Because of the concentrated heat production, you will almost always want to put the bulb in a hood and also provide some sort of cooling to prevent heat from beaming down onto your plants and driving up the ambient temperature of your tent/grow room. This is especially important for the bigger lights with power above 250W.

Additional setup: As a result of the heat mentioned above, most growers use an exhaust fan with ducting to vent out heat.

More parts/complexity: HID lighting means a few more parts than other types of lighting. Fluorescents are just the bulb and a fixture and most LEDs are just the light itself. But most HID setups have at least a bulb, fixture, external ballast, and an extra cable if you don’t count the exhaust systems parts, too.

Light Emitting Diode (LED) Grow Lights

Today’s LED models are much better for growing cannabis than the ones available even a few years ago. Many modern lamps are full spectrum or “wideband”.

LED grow lights

Other spectrum colors like red, far-red, and infrared are important for the budding/flowering stage. LED manufacturers have developed specialized lenses to point the light directly to the plants and increase penetration, resulting in bigger yields for the same amount of light compared to older models.

Highly customizable LED light setups are great tools for manipulating flower quality, especially if you are growing organically.


Cooler Temperatures: LEDs almost always have built-in cooling that pushes heat up and away from the. As a result, LEDs run very cool and many growers can get away without venting heat at all.

Versatility: The smaller size LEDs can be plugged directly into the wall and hung up over your plant, without needing to do anything else.

Cutting Edge Technology: Some growers believe LEDs produce more resinous buds. Combining LEDs with HPS grow lights seem to be getting some growers great results, though more testing is needed.


Although the LED lamp itself usually does run a lot cooler than a similar wattage HPS bulb, they still produce heat and the bigger sizes like 300W+ may need to be vented with an exhaust fan to prevent the grow space from getting too warm.

Despite what some sellers may tell you, LEDs get slightly smaller yields per watt than HPS grow lights on average.

LED grow lights tend to need a lot of space between the lamp and your plants, which mean you need a tall, grow space to get the best results. Smaller LED panels should be kept 18″ or more away during the second half of the flowering stage to avoid light burning your buds, and some of the bigger models need to be kept 30″ or more away from the buds

HerbCEO Final Thoughts

Herb CEO Summary

Look, we’re not hear to tell you how you grow is wrong and you must follow this one absolute correct lighting method if you want your crop to flourish. Cannabis growing has never been about that and we hope it never will be. This industry needs experimenters, innovators, risk takers and independent thinkers willing to try different light types, arrangements, distances, intensities etc to produce new and exciting cannabis flower.

We hope you gleamed some value though in our rather condensed perhaps over-simplified outline of the main types of lightning used in grow rooms around the world, from smaller home-grow operations to massive industrial scales.

What lighting setup are you currently running? Care to share with other readers in the comments below? We love fostering community and are always open to new and varying opinions on the pros/cons of various lighting types, techniques and grow methods!

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