best grow lights for autoflowering

Best Light Spectrum to Grow Autoflowers

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

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

1. What is Light Spectrum?

The light spectrum is the different colors (aka wavelengths) 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 make up 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 wavelengths possible for the best development of our 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 plant from seed to harvest with any spectrum or amount of light but this can seriously affect your harvest.

2. Light Spectrums in Each Stage

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.

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

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

Light bulbs emit a limited scope of wavelengths meaning there are colors of the 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.

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 in the vegetative stage because they emit a “blue” light (aka colder light).

HPS bulbs are rated at 2000 Kelvin are usually used 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 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 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 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, 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 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 itself 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. Light Spectrums for Autoflowers

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, autoflowering plants start their life cycle in the flowering stage and depend solely on age to start producing buds. That’s why we recommend using a mixed 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 spectrum of light guaranteeing the best flowers and biggest yield.

5. In Conclusion

The light spectrum 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.

When growing autoflowering plants indoor we need to simulate the environment they naturally grow in. The environment includes humidity, temperature, and the mos

The Best Lighting for Autoflower Cannabis

There’s something genuinely satisfying about planting a seed in the ground and watching a cannabis plant seemingly appear out of nowhere, fed by the sun. Unfortunately, prohibition prevents many growers from doing just that. They have to take their growing indoors, away from the light source these plants were designed to use. Indoors growers have to pay for every lumen of light, and replicating the sun doesn’t come cheap. Thankfully, lighting solutions for cannabis growing have come a long way in the past ten years. Before, even the smallest growing operation would use as much power as an air conditioner or over-powered gaming PC, whereas today it’s possible to grow weed with bulbs that use less energy than the lights in your kitchen.

We covered each different kind of bulbs available in our article, How to Grow Autolfower Cannabis Indoors. Head on over there for a breakdown of the technology. Today we’re going to identify your needs and pick the best solution. Here’s a quick run-down of the options.

Fluorescent lights

The faithful standby for old-school indoor growers, there are multiple fluorescent lighting options from which to choose.

CFLs are those twisty bulbs you probably already have in your home. They can be found in any hardware store. Their ubiquity makes them an ideal solution for a discreet grower who doesn’t want cultivation supplies on his or her credit card statement. Their only downside is that while each bulb has relatively low power consumption, you’ll need several bulbs to provide enough light to grow ganja. Power consumption might reach over 400 watts to generate enough illumination.

T5s are what you probably picture in your head when you hear the word fluorescent. These long tubes of electrically charged gas have been around since the 1930s. Cannabis responds better to the T5 light spectrum than CFL’s, and they’re powerful enough to grow a plant from seedling to harvest. They’re a bit more conspicuous than CFLs, but it’s not unheard of for people to have homes lit by T5 lights, especially in East Asia.


HID bulbs blast out massive amounts of light, and you’ll notice it in your plant’s growth if you decide to use them. They utilize the perfect spectrum for cannabis cultivation, but they also generate large amounts of heat and use a great deal more electricity than other options.

Metal Halide

Rarely used for the length of a full grow, metal halide lights provide the ideal blue spectrum for vegging cannabis plants, but many growers switch to HPS come flowering.

After vegging under metal halide, growers will often switch to high-pressure sodium lights for flowering. In terms of electricity used per unit of energy for the cannabis plant, the MH/HPS combo is the best option. However, neither of these lights come cheap, and while they may be efficient in relative terms, they still use a great deal of power in the process, and you’ll see it on your electric bill.


LEDs are the perfect low power solution for growers with smaller tents and those growing with discretion in mind. Their low power usage means you’ll barely see an uptick on your electricity bill, at least if you’re only using one or two lights.

Traditional LEDs are giant arrays of bluish-purple lights that looks like something from a science fiction movie. Their not as efficient as HID bulbs, but their low power consumption more than makes up for this fact. The biggest downside is that the purple light wreaks havoc on cameras, meaning you’ll have to turn them off to get beautiful pictures of your hard work.

Chip on Board lights are tiny LEDs that put out an intense white light. A single 100w cob light is enough to power a small grow tent by itself and will only run you $100. If you’re looking to grow on the cheap, COBs are even better than CFLs regarding power consumption and just slightly more expensive at retail.

What’s Best For You?

That’s a quick summary of your options, so what’s the Best Lighting? It depends on what you value.

If you want to save on start-up costs: Four to six CFL bulbs are your cheapest option, but you’ll pay for it in power consumption later.

If you want to save on electricity: A 100-watt cob light will use the same amount of energy as a single old-school incandescent bulb would have. If you don’t want to see your energy costs increase, COBs are your best option.

If you want the largest yield: For yield, HID can’t be beaten. While you’ll pay a pretty penny to procure and run them, they’re the only option that can come close to competing with the sun. HIDs will produce more grams of cannabis produced per watt of electricity used than any other option.

There’s something genuinely satisfying about planting a seed in the ground and watching a cannabis plant seemingly appear out of nowhere, fed by the sun. Unfort