led autoflower grow

Can You Grow Autoflowers with LEDs?

Even as a beginner, you’ve probably heard of LEDs. LEDs were introduced just a few years ago, and growers wouldn’t even consider growing marijuana plants because they weren’t as good as other high-intensity lights in the market. However, just like people changed their minds regarding autoflowers, LEDs managed to turn around and produce great yields.

Autoflowers are easy to grow, despite what you’ve been told. They adjust to any growing condition as long as it isn’t extreme. Similarly, they will grow no matter what light you use, but obviously, stronger lights equate to stronger plants, better quality, and higher yields.

1. Can you grow autoflowers with LEDs?

Yes, of course, you can! In fact, you can grow any type of plant using LEDs without any issues. They last for a long, long time with some lights continuing for more than 50,000 to 100,000 hours!

Even though LEDs are different from bulbs, both of them fit the same purpose when talking about Cannabis. Obviously they have their differences but are used to grow autos and photos alike, some growers even mix LEDs and light bulbs in the same tent with great results.

Here’s a quick example of how your autoflowers might fare under LED lights:

As you can see, the color combination ends up looking white, that’s what you should look when buying LEDs. The plants are super healthy, the buds are quite dense and the plant is strong, that’s what you can expect when using good-quality LED fixtures.

2. What are LED Lights?

LEDs have been around for a while but only recently their popularity has increased, as technology advances, LEDs have been developed for other uses, and growers have benefited from that. But what exactly are LEDs?

LEDs – Light Emitting Diodes – are lights that can be used to grow almost any type of plant. Technically speaking, it contains two semiconductors – electrons and holes. While electrons are negatively charged, the holes are positive. When an electric current is applied over the light, the two semiconductors collide with each other and release energy, otherwise known as photons.

This entire process is known as recombination. The LEDs introduced at the very beginning weren’t of any advantage to a grower since the light output was meager compared to other lights; however, with technology and years of research, many manufacturers now produce outstanding LEDs that almost mimic the sun’s full spectrum.

Types of LEDs

Standard purple LEDs

These were the first LED fixtures available and are still widely available today, and although they’re not the best you can still get good results with them for cheap. This type of LEDs is the cheapest out there but lacks in build quality, light quality and sometimes can result in lower yields. When growing with this type of LED, you can add complemental horizontal lighting with the proper led strip spacing or vertical lighting with light bulbs to provide good light to the lower part of the plants.


Cob LEDs (aka chip on board) is a bit more expensive than standard lights but has a better penetration due to their intensity while being relatively efficient. The only drawback is that they don’t have a good coverage due to their format, so you’ll need a bit more to properly cover your growing space.

Spread or spider-style LEDs

These types of LEDs are the latest in LED light fixtures, due to their format they can cover a big area and are widely used in commercial operations due to their high efficiency and wide light spectrum. With this type of LED fixture, you’ll get the most gram per wattage and efficiency but can be extremely expensive.

3. The advantages of using LED lights

When compared to bulb fixtures , LEDs are a tad more expensive. Then why choose them? Well, LEDs may be a little more expensive than HPS or HID lights when you first purchase them, but the efficiency reduces cost in the long term, making LEDs certainly cheaper than maintaining HPS lights.

  • Full-spectrum

The spectrum refers to a light source that covers the wavelengths that are useful to animal and plant life, from infrared to ultraviolet. Obviously, no artificial light can mimic the sun but when talking about a full-spectrum light it means that it emits the entire visible spectrum and the important qualities of natural light.

Even though not all LEDs emit all the wavelengths, you can find full-spectrum LED fixtures that will surely make a difference in the quality of your harvest. Cannabis plants produce trichomes to protect the flowers from UV rays because that’s where the seeds will develop so if you’re growing with a good quality LED your plants will end up having more resinous and denser buds than with light bulbs.

  • Less Heat

LED fixtures will emit less heat than bulbs while emitting the same light intensity and drawing less power, you can easily find LED fixtures that come with fans but usually, it’s not needed as long as you are dealing with good quality diodes, and have fans and an extractor properly working in your growing tent.

  • More efficient

Due to LEDs being more efficient, they can produce an equivalent to light bulbs using less energy. LED fixtures use up to 75% less energy while producing the same or even more light intensity. As an approximate guideline, LEDs use 12w to emit an equivalent to a 50w bulb.

  • More lifespan

LEDs have a lifespan of more than 50,000 hours, some even reaching up to 100,000 which is way more than bulbs, this is due to the low temperature of most fixtures. Light bulbs emit a lot of heat which reduces their lifespan, this means that although bulbs are cheaper you will have to replace them more often so LEDs are cheaper in the long term.

4. The disadvantages of using LEDs

Light is vital in the photosynthesis process which is equal to food for cannabis plants, and it’s extremely important for autoflowering plants that have a short lifespan. Now that you know why LEDs are so awesome, you might be interested to know the disadvantages as well.

  • Expensive

As mentioned already, the cost of LEDs is a bit more than other lights such as fluorescents, HPS, and MH lights. However, the LEDs that are being introduced now are so competitive that the prices have dropped down drastically .

The manufacturing market is saturated with too many LED manufacturers and it is indeed possible to purchase cheap LED lights. But, if you love big, thick buds then you have to go for the ones manufactured by brands that are a bit expensive.

  • Not all companies provide a complete spectrum

Most companies provide a complete spectrum of light; however, it’s recommended that you do your research before purchasing lights because some companies aren’t very technologically advanced yet. If you do purchase an LED, make sure that it comes with all the colors required for your lovely autoflowering cannabis plants to grow.

  • Directional light

Even though this has been fixed in newer fixtures, the light emitted by some LEDs is directional (like a flashlight), this means the area covered is less than when using bulbs, although manufacturers describe the coverage for vegetating and blooming plants so you will know everything you need to know before buying them.

  • Aging diodes

As time passes by LED diodes can start to change color, even though they can last more than 50,000 hours, they can fail or even burn.

If you invest a little more ina better quality you’ll avoid having to fix it for a long time, usually branded LEDs are made with good diodes which can last years and years without a problem.

Problems with individual diodes are more common with cheaper LEDs but if you can invest a little more and buy a good fixture it’s unlikely it will happen.

5. How to grow autoflowers with LEDs

A major advantage of using LEDs is that you don’t have to change the light to match the stages of the plant. For instance, the plant needs a lot of blue light in the vegetative phase and more red light in the flowering stage . In such stages, growers use MH lights and switch to HPS lights during flowering. Even if you use CFLs, “Cool Blue Daylight” lights are used specifically in the growing phase.

Since LEDs contain all the colors (full-spectrum) , there’s no need to switch the lights between phases. But, remember that this is true only with certain lights because some LEDs being introduced now come with separate vegetative and flowering switches. No, you don’t have to switch to a different light, but you may have to manually control the switches.

Best LEDs for autos

There isn’t the best LED for autos, as longs as it’s a good quality fixture you’ll be fine. When buying an LED, remember that not all of them emit the whole spectrum so have that in mind, we also recommend you read all the information about it, like how much space they cover in the vegetative stage and in the flowering stage, check for the listed wattage and the actual wattage (which is how much they actually draw from the wall) and read a lot of reviews about it, this will help you decide on the best one for you.

Remember that LEDs are quite intense so when growing autos with them you should be careful, although autos aren’t affected by light toxicity as much as photoperiodic plants but ideally, you should grow in a lightproof space.

6. Things to keep in mind when growing autoflowers with LEDs

Light distance to plant

Growing seedlings with LEDs can be a little tricky. Seedlings are very fragile, and if the lights are too close, they tend to burn. Conversely, they grow tall and lanky if the lights are far away. So, the trick is to maintain the perfect distance between the plant and the light.

This is why many growers use T5 fluorescent lights, CFLs, and MH lights to tend to seedlings. However, if you plan to use LEDs for the entire cycle, you need to be very careful at the beginning. For starters, read the manufacturer’s instructions carefully.

Most lights are placed at a distance of at least 18-22 in (46-56cm) away from seedlings, and you can do that too. Once you observe how the plants react, you’ll be able to judge the distance yourself. Autoflower seedlings need to be observed much more because the plants can get stunted if the tender leaves get burnt.

Watts per plant

Despite LEDs being more efficient, you still have to provide at least the minimum wattage needed for your plants to develop properly. If you don’t want to spend too much, you can get away with providing the minimum amount of LED watts (and the equivalent for bulbs) per plant as listed below.

  • 1 plant – 18w ( 75w)
  • 2 plants – 36w ( 150w)
  • 4 plants – 72w ( 300w)
  • 6 plants – 108w ( 450w)
  • 8 plants – 180w ( 600w)
  • 10 plants – 216w ( 750w)

When dealing with this, you need to have in mind that the listed wattage is not actually the power LEDs draw from the wall so we added the light bulb equivalent in case the manufacturer doesn’t provide the actual wattage.

Listed wattage vs actual wattage

Manufacturers usually claim their LEDs are 1000W or 2000W but that’s actually the LED equivalent to bulbs, when looking to buy an LED, you should also look at the actual power that light fixture draws from the wall, as said above, 12w is equivalent to a 50w bulb so by having that in mind, you can take a look at this chart to help you choose the one that’s suited for your growing space.

Wattage per Cannabis Plant

Number of plants LED (optimal) Light Bulb (optimal)
1 24w 100w
2 48w 200w
4 96w 400w
6 144w 600w
8 192w 800w
10 240w 1000w

By following this table you can properly provide the amount of light needed for your cannabis plants, flowering with the optimal wattage will result in healthier plants, better quality flowers, and a bigger yield.

Remember that this is an approximate and the amount of light may change according to your growing space, size of plants, and other factors.


Autoflowers have a lot of growing to do and they do it very fast. So fast that you’ll be on your toes to keep up with it. If you want the very best yields, you must be prepared to work for it. And talking about maintaining the plants, heat plays a major role.

Autoflowering cannabis plants thrive in environments where the temperature is neither too cold nor hot. If the temps exceed 35°C, the yields diminish quickly and the buds begin to burn too. Similarly, they cannot stand temperatures that go below 15°C.

Fortunately, you can play God when growing indoors and control the temperatures. But, it becomes easier if you plan it well. For instance, some lights like HIDs emit a lot of heat and the temperatures soar pretty quickly.

Even though it’s not that common, some LEDs exhibit similar tendencies and produce too much heat. Therefore, make your life easier by purchasing lights with inbuilt fans to reduce the heat.

Use lights with better features

LEDs offer so many features that it can be mind-boggling. From dimming to power efficiency to a full spectrum, they appear to be the perfect companion to your autoflowering plants. However, while some companies offer all the features, they come with a price tag.

If you’re really interested in quality yields, though, look for lights that offer ‘dimming’ features. Some lights come with knobs that can be used to adjust the brightness of the light. For example, plants need less light during the vegetative phase and more light during the flowering phase so to save energy and money they can be dimmed. However, if you absolutely cannot afford such lights, it’s still okay because the plants will grow even if you don’t dim the lights.

Research, research, and more research

The only way to grow excellent plants is by choosing great lights. And you need to do a lot of research to buy lights that suit your setup. LEDs are available in various sizes and watts, and the differences in costs and features can be jaw-dropping. For instance, a branded 300W light can cost anywhere from $80 to $100, bigger brands offer the same at $350 but even newer ones can reach up to $1000 due to the research they’ve made and the money invested in making the best possible fixture they can .

Remember that not always the more expensive LEDs are better so make sure you research a lot before buying your light fixtures.

If you dig a little further, you’ll be surprised – nay, shocked – to find out that some brands offer 1000W lights for just $70 and others sell the same wattage LED for up to $1500 ! Amazing, eh? Obviously, there are differences in how the lights perform, and it’s up to you to figure out what your plants truly need.

7. In Conclusion

You don’t need the best lights in the market to grow good cannabis but if you want to stay updated with the latest technology and improve your harvests, LEDs are the way to go. Not only it will improve your harvest but will also consume less energy, making up for the initial investment in the long term. If you have changed from bulbs to LEDs and noticed a difference, feel free to share your experience in the comment section below!

This post was most recently updated on August 28, 2020.

LEDs have come a long way since they were first introduced, what used to be considered worthless is now the most advanced product in cannabis growing.

Best Light Spectrum to Grow Autoflowers

When growing autoflowering plants indoors we need to simulate the environment they naturally grow in. The environment includes humidity, temperature, and the most essential of them all: light.

When growing indoors, the best light spectrum is one that comes as close as possible to the sun’s spectrum, so basically, a full spectrum.

Either you prefer light bulbs or LEDs, you need the right light spectrum in each stage for optimum growth.

1. What is Light Spectrum?

The light spectrum is the different colors (aka wavelength) a source of light can emit. Light is measured in nanometers (nm) and each nanometer represents a band of light (a band of light is a section in the color spectrum). Humans can see a small part of the spectrum, between 380 to 780 nanometers, which means we can only see the colors ranging from violet to red.

Even though it appears white, the sun is a full spectrum light source and contains the whole spectral wavelength. That’s why rainbows happen. When raindrops refract light into individual wavelengths you can see all the colors (visible to humans) that makeup sunlight.

In nature, cannabis plants grow under the sun, receiving the whole spectrum of wavelengths. This means we have to provide the maximum amount of wavelength possible for the best development of our cannabis plant.

Although it’s not essential, it is considered good to provide the best light spectrum to encourage plant growth.

Remember this is not a rule, you can grow your cannabis plant from seed to harvest with any light spectrum or amount of light but this can seriously affect your harvest.

2. Light Spectrums in Each Stage

Best light spectrum for growing plants

During the vegetative stage, cannabis in the wild needs blue wavelengths to grow strong, big, and promote leaf growth. When growing indoors we aim to grow as many leaves as possible. With more leaves, there is more surface to absorb light, this way we ensure our plant develops a strong stem and branches preparing her for the flowering stage.

Best light spectrum for blooming plants

When entering the flowering stage, cannabis in the wild uses red wavelengths to promote bud formation. If we want to produce dense buds and increase yields we need to provide the plant red wavelengths, this will increase the rate of photosynthesis thus increasing bud formation.

• Tip: When experimenting with training, using “red” light will make plants grow taller, making it easier to train.

The general rules are “blue” light = shorter and stronger plants with more leaves, “red” light = taller and weaker (when compared to plants grown under “blue” lights) plants with fewer leaves.

3. Types of Light

Cannabis grow lights are usually divided into two kinds, light bulbs, and LEDs.

Light bulbs emit a limited scope of wavelength meaning there are colors of the light spectrum they don’t emit, therefore they are narrow-spectrum lights.

LEDs emit almost all the colors in the spectrum, they are composed of blue, red, and white diodes allowing them to emit all the wavelengths of the spectrum, therefore making them full-spectrum lights.

LEDs vs Light Bulbs

LEDs Bulbs
Expensive Cheap
More efficient Consume more electricity
Take less space Need more space
Runs cooler Emit a lot of heat

Light Bulbs: HPS, MH, CFL, and HID

Light bulbs come in four types: Metal Halide (CMH), High Pressure Sodium (HPS), Compact Fluorescent Lights (CFL) and High Intensity Discharge (HID).

MH bulbs are rated around 6500 Kelvin and are usually used for cannabis in the vegetative stage because they emit a “blue” light (aka colder light).

HPS bulbs are rated at 2000 Kelvin are usually used for cannabis in the flowering stage for their “red” light (aka warmer light).

CFLs are rated at around 5000 Kelvin, they emit a very weak “blue” light and are only used with cannabis seedlings and clones as they just need to develop roots for the first couple of days when the vegetative stage begins they should be transferred to a growing space with stronger lighting.

HID can cover from 3500 to 5000 Kelvin, they are similar to HPS but contains xenon inside, thus emitting a different light spectrum and are more efficient while being more compact.

• Tip: You can also grow your plants under both CMH and HPS bulbs, this is called a mixed light spectrum and will ultimately result in a better harvest.


• Cheaper than average LED lights

• You don’t need to change the whole fixture, just replace the bulb


• Electricity cost is higher if compared to LEDs.

• Need extra equipment for cooling.

• Requires changing bulbs (CMH to HPS) when entering the flowering stage.

Full Spectrum LEDs, and Infrared and UV Lights

All LEDs are full-spectrum lights unless advised, they may not contain all wavelengths but will emit the needed amount for each stage of cannabis plant growth, unlike light bulbs, you won’t have to change anything other than your timer when you’re about to enter the flowering stage.

You can find full-spectrum LEDs that have UV and infrared diodes, if not, there are LEDs designed to emit those spectrums. They’re not that common in cannabis indoor growing but are said to benefit growers.

Just like everything else on the planet, cannabis plants are damaged by too much UV light but at the right amount. It can promote trichome production as the cannabis plants produce trichomes to protect themselves from too much light.

As UV lights, infrared lights can harm your plants in excess but at the right amount, it can boost photosynthesis, affect yields, plant growth, and plant health in a positive way.


• Used on the entire life cycle.

• Longer lifetime than bulbs.


Note: It’s unusual to have UV and Infrared lights, they’re expensive and are NOT essential for growing good flowers. They’re recommended for more experienced growers who want to experiment with different spectrums.

4. The Best Autoflower Light Spectrum

As most of you already know cannabis plants have two stages: the vegetative stage, and the flowering stage, needing a different light schedule and spectrums in each one of them.

Unlike photoperiodic cannabis plants, autoflowers enter the flowering stage automatically and depend solely on age to start producing buds. That’s why it’s essential to choose your cannabis light spectrum carefully, we recommend using a mixed light spectrum of warm and cold light bulbs (CMH and HPS) or a full-spectrum LED during the whole lifecycle of your autoflower.

This way your plant will receive a complete light spectrum, guaranteeing the best flowers and biggest yield.

5. Light Spectrum FAQs

What are “blurples”?

Blurples are LED fixtures that emit a purple light, in general, these lights claim to be full-spectrum but actually only contain blue and red diodes that emit specific wavelengths.

These lights can be used to grow cannabis but you need to have in mind that they do NOT emit a full spectrum, they’re just emitting a small part of the blue and red light spectrum so make sure you research before buying your new LED.

Which wavelengths are essential for cannabis?

When looking for a light fixture, you should make sure that the 440nm and 660nm wavelengths are at peak, meaning that your lights should emit more red and blue than the others but should definitely provide all of them. If you don’t know or the manufacturer doesn’t specify it, don’t doubt to send them an email, most respectable companies will provide this information.

What is cool and warm light?

When talking about lights, “cool” or “warm” refers to the light spectrum, which goes from violet to red. So, cool colors are on the lower end of the light spectrum and include colors such as violet, blue and green while warm colors are on the higher end and include yellow, orange, and red.

What’s the best light spectrum for seedlings?

As you may know, cannabis seedlings are in the vegetative stage so they will react better to blue or cool lighting. If there’s not enough blue light your seedling may end up stretching too much so even despite not needing a lot of light power, you should provide the right spectrum. If you don’t want to use high-intensity lights or you cannot dim down your LED, you can use 50w CFL bulbs for seedlings and clones until they’ve grown enough to be transferred to a more powerful light fixture.

6. In Conclusion

The light spectrum for weed is a small part of a much bigger system, there’s nothing as better light for your plant. But remember, the final product does NOT depend solely on your light.

Depending on which type you choose, either an LED or bulbs, you’ll have to adjust your growing environment accordingly to guarantee the best result possible.

This post was most recently updated on December 29, 2020.

What is the best light spectrum for cannabis and what spectrum is better for each phase of a cannabis plant's life cycle.