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Best Light Spectrum to Grow Autoflowers

4 weeks ago
5 min read
Best Light Spectrum to Grow Autoflowers

Your only goal when growing cannabis plants is to create such an ideal setup that the plants grow without any problems and produce the best yields. Truly, nothing else matters. But, to achieve this goal, a number of important factors come into play and light spectrum is one of them. This article will give you an insight about the best light spectrum to grow autoflowers. It also applies to other types of cannabis plants, but we will talk about autoflowers alone.

The color spectrum of the lighting you use is a big deal for cannabis plants. But, what’s so important about it? Well, that’s how the plants grow. You can’t just use any type of light to grow cannabis plants indoors, can you? They have to resemble the spectrum of natural light – sunlight. Sunlight looks white to the naked eye but it’s actually made of several colors.

Plants grow according the color spectrum. They use it as a signal to flower or continue growing. Cannabis plants depend upon the photoperiod. Thus, when the spectrum is mostly white, they continue growing. But as soon as the light changes (seasons change) and they receive red light mixed with white, they treat it as a signal to start flowering.

Not every cannabis plant behave this way, though. Cannabis Sativa and Indica plants certainly grow based on the type of light they receive but Ruderalis is a little different. They grow based on a specific schedule and start flowering automatically after the plant is about 8-9 weeks old. Some autoflowers will flower in the 7th week while some may flower during the 10th week. There will be a few differences but it’s obvious that they flower based on the age of the plant rather than depending on light.

Having said that, autoflowering cannabis will also grow amazingly well if you use the right spectrum during its vegetative and flowering stages. Since you have complete control over every operation while growing plants indoors, you can ensure that your plants have the best opportunity to perform as best as they can.


The light spectrum is important whether you’re growing autoflowering or photoperiod plants. Although autoflowers don’t grow or flower based on seasonal changes, the right spectrum ensures that the plants grow well and produce great yields. Sure, you don’t have to switch cycles manually but the plants won’t respond well if you use the wrong spectrum.

But, why do cannabis plants care about the spectrum, anyway? In the wild, the light spectrum is the only way for the plants to determine their growth.

During summers and even spring for that matter, the spectrum is whiter with a mix of blue light. The sun is closer to the earth and plants love all the bright light they receive.

As the light becomes brighter, the leaves begin growing larger. The plant tries its best to absorb all the light and produce as many leaves as possible. This spectrum of white combined with blue is the perfect spectrum for the plants during the growing or vegetative stage. Since you need to mimic the spectrum indoors as well, you’ll need blue light mixed with white.

If you’re using CFLs, use cool blue or warm white. If you’re using HID lights, go for Metal Halides that produce blue and white. This will ensure that your autoflowers produce big leaves.

As the seasons change, you’ll notice that the light gets dimmer outdoors. Summers usually have bright light but it reduces as winter approaches. This means that the plants no longer receive white bright light, and they use this as an indication to start flowering. The spectrum of light is red mixed with white, and as the plants are exposed to red light they produce buds.

Although autoflowers don’t depend on seasonal changes, it’s necessary to note that they will perform way better if you use red lights as soon as they start flowering. The buds develop faster and grow fatter with red light. The difference between autoflowers and photoperiod is that photoperiod plants won’t even flower if you do not provide red light spectrum.

To replicate this in the grow room, use HPS lights that produce yellow or reddish light when your autoflowers start producing pistils. Warm yellow CFLs will also do the trick. If you love using LEDs, look for lights that offer both blue and red lights so the autoflowers can grow without any hindrance.


You’ve probably never heard of green light in the spectrum. Green light helps the plants to grow more leaves. It’s an important part of the spectrum that primarily helps plants during the vegetative stage. It penetrates the canopy and helps in photosynthesis as much as blue lights if not more.

To add green lights in your lighting equipment inside, you need to purchase lights that offer color spectrum that includes green light. Most lights do not offer this, but you can opt for florescent lights that produce small amounts of green light.

However, if you don’t want to add fluoros, go for regular LED lights. Most LED lights are available with a full spectrum that comes with all the colors necessary for cannabis plant growth.

If you’ve noticed LED lights, some of them produce a purplish hue, and that’s only because they include purple light in the spectrum. Purple lights are added with red lights to ensure that the plant produce stronger and fatter buds. They promote bud production and the levels of resin also increases.

Although no other type of lighting includes purple lights, new LEDs in the market are absolutely brilliant and will help your plants produce more buds than you expected. Purple lights will also increase light penetration that results in stronger leaves and buds.


Many LEDs available today offer UV lights in the color spectrum. What exactly is a UVB light and what does it do? Well, growers claim that including UVB lights in the spectrum improves the levels of THC in the plant. The theory behind this is that it works similarly to how it affects humans. Just like UV rays affect human skin, it affects cannabis plants and forces them to produce a lot more resin. Thus, manufacturers – especially LED companies – produce lights including infrared and UVB lights.

Although the connection between UVB and THC isn’t scientifically proven, experts believe that it actually helps in raising THC levels. UVB lights aren’t available with all kinds of lights – CFLs, HIDs, etc – but almost all LED lights have both UVB and infrared lights. Sure, you won’t see a lot of UVB lights, but lights in small amounts will also do the trick when included in the spectrum.

Reading all this can be confusing, and we understand that. If you don’t want to break your head and understand the light spectrum, you can blindly go for full-spectrum lights that help autoflowers grow exceedingly well.

Sunlight is considered full-spectrum because it covers the entire electromagnetic spectrum including infrared. You’ll see LED companies offering full-spectrum with a list of all the colors included. Although you may not be able to see all the colors in the spectrum, you can be rest assured that they are there considering you purchase lights from a trusted manufacturer.

Autoflowers surely grow even under simple white lights, but a full-spectrum will ensure that they produce the best yields.