Lighting for Cannabis Plants — Everything You Should Know

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Added 09 June 2022

Light is food for your cannabis plant. 

Thanks to photosynthesis, your plant converts light that falls on its leaves into energy to grow better. So yes, light is essential, but for new growers, lighting can be a confusing aspect — it is vast, with a variety of factors, types, et al. involved. 

But don’t worry — you've come to the right place if you want to know more about light. Learn all you need to know about artificial lighting for your cannabis plant in this article.

Optimal Lighting for Cannabis

lighting for cannabis

Light is essential, and the best light for your plant is natural sunlight as it contains the ideal mix of UV rays. However, if you are growing indoors, your plant lacks the luxury of natural light.

Since cannabis plants need a lot of light, especially during their vegetative and flowering stages, you need to substitute natural sunlight with artificial lighting for better, stronger growth, and excellent yields.

Four factors determine an optimal light setup:

  1. Distance of light source from the plant
  2. Light’s intensity
  3. Light’s color spectrum
  4. And lighting schedule or cycle

Natural light ticks all the boxes — the season and subsequent daylight, including the intensity and color spectrum, and the light cycle are tailored for the plants. 

Light is made of photons, which have different wavelengths and frequencies. Our eyes are sensitive to light at 380 nm to 680 nm of wavelength, and cannabis plants are sensitive to light from 200 nm to 800 nm

But not all wavelengths within 200 to 800 nm contribute to photosynthesis. Instead, only certain photons activate the biochemical process. This light is called photosynthesis active radiation (PAR), ranging from 400 nm to 700 nm

When growing a photoperiod plant indoors, you need to ensure your lighting setup meets these criteria while producing PAR light, as discussed in the following section.

Indoor plants require artificial lighting by default, but you may also choose to use artificial lighting because it offers you more control over your plant’s growth. But simply placing a regular CFL bulb is not enough. You need to use the right grow lights, too.

Four Factors for Optimal Light Setup

lighting for cannabis plants

As discussed earlier, the four essential elements of light setup must be the first thing you tackle when setting up your grow lights. 

Light’s Distance from the Plant

Distance between plants and light

The light’s distance is crucial for optimal photosynthesis. If the light source is too far, your plant may not get adequate light, and if it is too close, your plant may experience light burn due to excess light. 

For example, if the light source is placed afar from the seedling, it can result in stretched stems as it tries to get closer to the light source. 

However, the right distance depends on the type of lights and your grow setup. For a basic guideline, here are the ideal distances for HID lamps based on their wattage:



Minimum distance

Ideal distance

Max distance


8 inches

12 inches

19 inches


9 inches

16 inches

25 inches


11 inches

21 inches

31 inches


Remember, wattage-based guidelines work only for HID lights. For LED lights, the process is entirely different, as discussed below.

Intensity of Light

The growth of your plant depends on the light it gets. Lack of light can lead to low growth potential and larf (low-quality buds) due to the plant not producing enough energy to sustain the bud sites. 

On the other hand, too much light can cause light burn on your plant and waste a lot of electricity. So, you need to choose a grow light that produces enough light for your plant.

In addition, you shouldn't rely only on the light’s wattage. A 200W LED will not produce the same quantity of light as a 200W HID or CFL light. Wattage is merely an indicator of how much electricity the light source consumes while running. 

Wattage became the industry standard way of measuring light quantity thanks to the prevalence of HID lights. This is because HID lights convert electricity into light at consistent rates, unlike LED or CFL lights. LED lights are more efficient, so wattage rules are void.

Measuring Light in Lux

To choose the right intensity, you need to understand lumen and lux. Lumen measures the light’s flow from the source, so a bright source has a higher lumen. And lux is the measurement of light on a surface. 

Again, the type of light you use determines the optimal light intensity in terms of lux. But as a general guideline, here is the optimal range of lux for your plant’s growth:


Growth stage

Min intensity (lux)

Ideal intensity (lux)

Max intensity (lux)

Vegetative stage




Flowering stage





Measuring Light in Photosynthetic Photon Flux Density (PPFD)

You can also measure the light that is ideal for your plant by focusing on photosynthetically active radiation (PAR), which is a measure of photons that activate photosynthesis in plants.

You can measure PAR in two ways: photosynthetic photon flux (PPF) and photosynthetic photon flux density (PPFD). Here, PPF is simply the measure of all the PAR photons in the light, and PPFD relates to PAR photons at a specific surface in one second.

The PPFD method of measurement is more suited for plants as it measures the light that can be used by your plant for photosynthesis.

You can measure PPFD using a PPFD meter, which tells you if your grow light is strong enough for your plant or not. Some smartphones can also measure PPFD, depending on their camera or light sensor. 

For optimal growth, you need a PPFD reading of:

  • During the vegetative stage (18/6): 308 to 617 µmol in 18 hours
  • During the flowering stage (12/12): 462 to 926 µmol for 12 hours

If you do not get the ideal lux or PPFD readings, you need to get bigger lights. 

Light’s Color Spectrum

light color spectrum

Next comes the color spectrum, i.e., the color of the light, which can also improve your plant’s growth. 

Visible light behaves as a wave, and each color has a different wavelength. For example, the purple color that we see is light with a wavelength of 400 nm. And light panels often show one dominant color.

For example, MH lights have prominently blue light, whereas LED lights can be configured to produce any kind of color. 

For cannabis, you need to set up the right colored light source for the best growth. This is because some colors influence photosynthesis better than others, making your plant grow faster and sprout bigger flowers. 

Here are the prominent colors your plant can benefit from depending on its growth stage:

  • Seedling stage: blue light
  • Vegetative stage: blue light
  • Flowering stage: red to far-red light

Many growers prefer using MH light sources during the seedling and vegetative stages as it mimics the blue-dominant natural light of the summer months. And during the flowering stage, they shift to HPS lights that produce more red light, which is great for flowering plants.

Of course, multiple lights for one season work for advanced growers, but if you are a novice grower, choosing a single light type works best in saving money and effort. 

For choosing the right light source based on the color spectrum, you must first understand Kelvin's degree and its impact on light’s spectrum or warmth. Kelvin degree is a measurement used to determine the color of light relative to a black backdrop.

Every reputable light manufacturer displays Kelvin degrees on its packing box, helping you decide better. Here, the lower the Kelvin degree, the warmer the light is (redder), and the higher it is, the cooler the light is (bluer). 

So, for optimal growth, choose lights based on the following guidelines:

  • For MH lights: 3,200K to 5,500K
  • For HPS lights: 2,200K

LED lights can be configured to various light colors, so you don’t need to worry about it. Just get an LED light and set it according to your plant’s growth stage.

Remember, this is just a general guideline. You need to select light based on your plant’s strain, grow room environment, et al. 

Light Cycle

cannabis light cycle

Finally, the light cycle is the amount of time your plant gets light during the day. You need to pay attention to this if you are growing a photoperiod plant as, with a light cycle, you can control its growth stages.

So, you need to first think of the light cycle for your grow room. The ideal lighting schedules for each growth stage are:

  • For seedlings: 24 hours of light 
  • For vegetative plants: 18 hours of light and 6 hours of darkness (18/6)
  • For flowering plants: 12 hours of light and 12 hours of darkness (12/12)

A seedling benefits from 24 hours of light as it can use that energy to grow bigger roots and stems, which can kickstart its growth well during the vegetative stage.

During the vegetative stage, your plant needs at least 18 hours of light to generate enough energy to grow its mass. While you can grow plants under 24 hours of light during their vegetative stage, it is generally not recommended. It can waste a lot of energy (and money), and many growers think plant benefits from a few hours of darkness. 

You can keep your plant in an 18/6 light cycle for as long as you want, but ideally, you should switch the light cycle to 12/12 once it grows half of its expected size. After the 12/12 switch, the long dark hours will disrupt the plant and trigger it to grow flowers.

During the flowering stage, longer dark hours are crucial because it lets the plant grow big buds. This is why you must ensure your grow room or tent is completely light-proof to prevent your plant from re-vegging. 

As for autoflowering plants, the light cycle does not matter much because it grows on an internal genetic clock. So, stick to the 12/8 or 12/12 light cycle, depending on your preferences and how big you want your autoflowering plant to grow.

Best Lights for Cannabis

cannabis plants under HID Lights

Apart from the four factors mentioned above, the type of light you use also impacts your plant’s growth. The most popular grow lights for cannabis are metal halides (MH) and high-pressure sodium (HPS) lights, but there are other popular types too like CFL and LED lights. Let’s take a look at them.

Fluorescent (CFL) Lights

CFL Lights

CFL, or compact fluorescent lights, are the most common type of light that you can buy even at a grocery store. A standard CLF bulb only costs a few bucks and can last up to a year, making it the best option for new growers.

Here, you can get daylight CFL lights with 6,500K for vegetative plants and those with 2700K for the flowering stage. And you can expect a yield of 0.3 gram/watt.

The benefits of CFL lights are:

  • They don’t cost much and you can buy them everywhere on the planet
  • They are easy to use and don’t require any specialized equipment, making them ideal for beginners
  • You can purchase them in various color temperatures
  • They are energy-efficient and do not heat a lot

The downsides of CFL lights are:

  • Comparatively, they have a low light output — only enough for a couple of plants
  • For the same reason, they are not the best lights for big buds
  • They have a lifespan of up to a year but are often shorter

High-intensity Discharge (HID) Lights

HID lights

HID lights include metal halide (MH) and high-pressure sodium (HPS) lights. The only difference between MH and HPS is that MH produces a cooler light spectrum while the latter produces more warm light.

So, many advanced growers use MH lights during the vegetative stage and switch to HPS lights during the flowering stage. If you are a beginner and don’t want to invest a lot of money and energy (pun intended), you can choose only HPS light or experiment with both.

The most popular HID light for cannabis is 600W HPS grow light, and you can purchase the same with a complete set that includes the bulb, reflector, and ballast. The entire kit would cost you around Euro 150.

While the initial cost is low, HID lights only run for a year and they consume a lot of electricity, which can get expensive really fast. And you can expect a yield of around 0.5 to 1 gram/watt.

The benefits of HID lights are:

  • HID lights cost relatively less than high-quality LED lights
  • They are easy to set up and operate for beginners
  • Their intense light ensures excellent yields
  • They are reliable and produce a consistent light
  • You can get many options specifically designed for the plant’s growth stage

HID lights’ downside includes the following:

  • Their intense light can potentially burn your plants, so you need to take extra precautions to prevent that
  • You need to invest in ballast and reflector, too
  • HID lights tend to degrade over time and need replacement
  • They consume a lot of electricity

LED Lights

LED Lights

The new leader of lights is LED. LED grow lights produce light spectrums that work for all growth stages, and many high-quality ones come with spectrum configurations, so a single light can work for the entire season. 

Plus, modern LEDs, like quantum boards or chips on board, can even surpass HID lights in terms of light intensity and penetration. And they have a lifespan of up to 100,000 hours!

But you need to choose high-quality LED lights to reap all the benefits, which can get a bit expensive but it is worth it in the long run. You can get decent LED lights for as low as €120, but they can cost as much as €2000 as well.

And you can expect a yield of 0.5 to 1.8 grams/watt, depending on the light’s quality and specifications.

The benefits of LED lights are:

  • They are super energy-efficient, so they save you a lot of money on energy bills
  • They also run cooler than other lights, so you don’t need to counter the heat with exhausts and fans
  • Since they are versatile and customizable, they reduce the risk of burning plants or subpar yields
  • They are also plug-and-play and require little to no elbow grease to set up

The downsides of LED lights are:

  • High-quality LED lights can cost you a lot of money
  • The lack of industry standards for LEDs means you have to do more homework before choosing one
  • Cheap LED lights are not as reliable or intense
  • Depending on the LED light, the yields can be potentially lower than HID lights

LEC or CMH Lights

CMH lights

Ceramic metal halide (CMH) lights are similar to HID lights but they use a ceramic arc instead of quartz, which is used in MH lights. As a result, these lights produce a natural color spectrum, while offering a longer lifespan and more lumens/watt.

While they can cost around €250 and up, they last twice as long as HID lights and can offer a yield of up to 1.5 grams/watt.

Here are the benefits of CMH lights:

  • They emit natural light, which makes it easier to spot issues on your plant’s surface
  • It produces UV-B light that is terrific for trichome production on the buds
  • They can easily be set up and operated

However, the downsides include:

  • UV-B spectrum is not safe for you, so you need to invest in eyes and skin protection
  • They can get expensive to buy and operate
  • They produce a lot of heat, so you need countermeasures to deal with the heat
  • They are not as powerful as HID lights

Choosing the Best Light for You

You can choose the light type that works best for you, considering your preferences, cannabis strain, number of plants, and capital you want to invest. 

If you are growing only a couple of plants or seedlings or clones, you can just go with a CFL light as they are adequate. But for a slightly bigger setup, an LED setup with 400W to 600W would be enough as it won’t produce heat or consume as much electricity.

On the other hand, if you have a large grow room with an advanced setup, you can go with HID or CMH lights. The operation cost of these lights makes up for itself by significantly increasing your yields by producing the right type of light for your plant.

How to Prevent Light Wastage?

Another essential aspect of lighting for cannabis is that you ensure all the light is utilized by your plant and not wasted. Wasted light can not only cost you a lot of money in energy bills but also reduce your plant’s exposure to good light.

So, the easiest way to ensure light is not wasted is by being more efficient with your light using reflective materials. Doing so salvages the light going around your plant and directs it back to the plant.

Some of the best reflective materials for this are here.


Mylar is a thin polyester film with a reflection level of up to 97%, making it one of the best reflective materials for light. However, this does require proper ventilation because it reflects radiant heat energy, too, and it is quite delicate to use and can get easily torn or creased.

Foylon film

Foylon film is a more resilient version of mylar as it is made of spun polyester reinforced with foil laminate. So, it does not crease easily and can last longer. 

Panda or orca films

Panda or orca films are reflective on one side and black on one side, and they can reflect up to 85% to 95% light. Plus, some of these films are water and mold-resistant.

The only difference between the two is that orca film contains white plastic microfibres, giving it better strength and reflectivity.

Flat white latex paint

Another simple reflective material is matte white latex paint as it can reflect up to 85% light. Plus, it is less prone to light hotspots and absorbs a lot of the heat while being super easy to clean.

Other less common reflective materials that can come in handy in a pinch are emergency blankets and aluminum foil. However, the materials mentioned above are much better at the job.

Also, avoid mirrors or styrofoam. Mirrors don’t reflect light in the correct intensity or pattern, and styrofoam while being a good reflector is prone to catching fire.

Summary: Lighting for Cannabis Plants — Everything You Should Know

A good light source with the right color spectrum, intensity, and placement is essential for the healthy indoor growth of cannabis. Without good lights, your plant may not grow as vigorously or reward you with bountiful buds. 

So, when choosing a good light, ensure you use the best lights that suit your preferences and plant’s needs. The light should be placed at the right distance, throwing the right spectrum of light at the optimal intensity, and working at a preset light cycle.

Additionally, explore your options between CFL, HID, LED, or CMH lights and choose one that works best for your setup. Whichever option you choose, ensure it is high-quality and meets your electricity budget. And look for lights that produce the ideal levels of lux or PPFD. Again, investing in a lux or PPFD meter is a wise option.

And take some measures to optimize your light distribution and lower wastage by choosing a reflective material like mylar, orca film, or flat white paint. 

That’s it. Do these things and you are setting your plant on the right path to terrific growth and yield.



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