uv light for growing weed

Best Cannabis Grow Light for Beginners

Growing cannabis can be tricky as a beginner, as there are a lot of factors you have to keep in mind. One of the most important, though, is light. Specifically, you need to make sure you’re picking the ideal light for your strain and grow space, and that you’re keeping those lights on a precise schedule. Here’s everything you need to know.


With seeds ready to be germinated, pots ready to be filled, and your grow room ready for a long, rewarding season, you may be feeling ready to cultivate some cannabis. You’re just missing one more vital component: the lights!

It may seem like you can just use any sort of grow light and achieve sufficient results, but that’s far from the truth. Different lights are calibrated for different plants and grow spaces. Some may not provide enough light, causing wilting and poor development, while others exude too much heat and cause burning. Others still may hit the sweet spot in terms of supporting growth, but bleed cash in terms of energy efficiency.

It can take quite some time to do research on the right types of lights for cannabis, especially when you don’t have much experience growing. Thankfully, we’ve taken care of the legwork for you, and we’re happy to walk you through what makes a perfect grow light for beginners.

Why Is Light Important for Growing Cannabis?

Light is vital to photosynthesis, and thus essential to the growth of almost all plants. But, the specifics of how cannabis plants receive light are especially important.

For instance, photoperiod cannabis (non-autoflowering cannabis) grows best when it receives a particular amount of light hours per day, usually 16 or more, during the vegetative stage of growth. Once plants hit the flowering stage, that light requirement changes to around 12 hours per day. This, of course, is in line with the shift in sunlight hours that occurs in the spring, summer, and fall.

With that external signal, female cannabis plants (that haven’t been pollinated) know to start shifting their energy towards producing resin-loaded buds. If they don’t receive that signal, however, they won’t know how to distribute the energy they take in from the sun, and your yields will end up smaller than they otherwise would.

In turn, if you’re growing your weed plants indoors, it’s vital to ensure that your grow lights not only simulate the sun’s energy output, but shine on the same schedule as well.

What’s the Best Type of Grow Light for Beginners?

Considering just how important light is in the growing process, beginners should focus on getting a light that not only helps them achieve high yields, but saves them money as well. After all, starting up an indoor growing operation at home can be expensive, even on a small scale.

So, what lights fulfil that role? Well, there are plenty out there that will deliver fine results, and plenty others that’ll save you money, but the only ones that balance both efficiency and power are lamps fitted with LEDs, or light-emitting diodes.

The Benefits of LEDs for First-Time Cannabis Growers

As we just mentioned, there are many benefits beginners can enjoy if they opt for LEDs. Below, we’ll break them down in full.

LEDs Run Cool Despite High Energy Output

With LEDs, depending on which you select, you can achieve comparable energy output to HID, but without nearly as much heat! Thanks to the efficiency of the system, which we’ll speak more on later, all the energy it takes in is directed through hundreds of little lights. Far less gets wasted.

Less Heat Leads to Decreased Water Usage

Thanks to minimal heat in the growing room, you can also expect the water you give your plants to last longer than it normally would. Since you don’t have to deal with rapid evaporation, your watering schedule will not only decrease, but become more efficient.

If anything, all you have to worry about when growing with LEDs is overwatering.

Decreased Water Usage Leads to Fewer Nutrients in Turn

Since many growers include their plant’s nutrients in their water, decreased water usage will also lead to decreased nutrient usage. That, again, is thanks to the fact that plants are able to use said water and nutrients more efficiently.

LEDs Allow for High Light Intensity

The low heat output of LEDs allows for yet another benefit: the potential to offer your plants higher light intensity. See, rather than intense light, it’s intense heat that is the main culprit behind burning plants. If the plants can enjoy more intense light without worrying about heat, however, they can take in a lot more energy.

LEDs Are More Energy Efficient Overall

Lastly, thanks to the fact that far less energy gets wasted on creating heat, LED lamps are the most energy efficient option (relative to their power) of any type of grow lamp. Along with that, you don’t need to have as powerful of a vent or cooling system to account for heat, which you’d need with HID lamps, so you take up even less energy as a result.

What Size Grow Light Do You Need for Cannabis?

The next thing you might be wondering about, then, is what size light you should get. Now, this will depend on the actual energy output of your LEDs (which can vary), along with the quality of your lamp, but there’s a good general outline you can follow as a starting point.

Specifically, assuming you have a decent-quality lamp, you should ensure you get a light with a coverage area of 50 watts per square foot (538W/m²) of growing space. If you were growing in a space that was 5 feet long and 5 feet wide, you’d need a 1250W LED light. That isn’t an exact measurement, of course, and you’ll still need to verify the specifics of your lamp and grow space. In turn, you should check the manufacturer’s guide, and see how they describe their product’s performance.

How Much Do Grow Lights Cost?

Speaking of one’s lamp of choice, though, how much should you expect a grow lamp to cost? Well, keeping the focus on LEDs, you’ll see a great amount of variation in cost.

You can find certain lamps that are cheaper than the vast majority, coming in at well under €100, but they’ll often be low-quality and prone to early burn-out. There are plenty of high-quality LEDs out there, though, some of which can last up to a decade. However, you can also expect to pay quite a bit, sometimes in the €1–2,000 range, for the best and largest options.

In turn, you also have to consider what running the light will cost you once you instal it. Cheaper lamps won’t take up that much energy, but they also won’t offer especially powerful light, so you’ll end up paying more, in a sense, by missing out on optimal yields.

Higher-quality lights may be more expensive out the door, but you’ll know your plants are getting plenty of light, which they’ll be able to convert into massive amounts of buds. You’ll also not have to worry about the increased energy cost of plugging in multiple weaker/low-quality lights.

However, more powerful lights will naturally need more energy to run, and especially powerful lamps will emit enough light to warrant a cooling and ventilation system. That, of course, will lead to a significantly higher energy bill than otherwise.

Beginner-Friendly Lighting Accessories

With your mind more settled on what sort of lamps you’ll be getting, it’s time to think about what accessories you’ll need to install and help them run efficiently.

Adjustable Rope Hangers

Before you get your growing operation off the ground, you need to get your grow lights off the ground. In that moment of need, you should seek out some adjustable rope hangers to carry your lights to the top (of your grow room).

Adjustable hangers are especially useful, as you can adjust the light intensity your cannabis receives depending on its phase and development. If your plants need some extra shine, you can lower the lights towards them, then bring them back up when things get a bit too warm.

Wi-Fi Timer

Timing is another major responsibility that comes with your grow lights, and sometimes you can’t trust yourself to turn them off and on at the right times. When the rest of the growing process gets too overwhelming, consider getting a Wi-Fi-linked timer to turn your lights on and off at precise intervals.

As we’ll further explain in a bit, this sort of timer is especially useful when you need to adjust the light hours between the vegetative and flowering stages of growth. There’s no need to worry about forgetting the schedule when your timer remembers it for you!

How Much Light Do Indoor Cannabis Plants Need?

There are different requirements depending on whether you’re growing photoperiod feminized strains or autoflowering strains, and we’ll discuss them accordingly.

Feminized Strains

If you’re growing a photoperiod feminized strain, you’ll need to change your light schedule based on the phase of development.

During the vegetative stage, they’ll need anywhere from 16–20 hours of light per day. The short nights tell your plant that it needs to spend its energy on getting tall and spreading its leaves, allowing it to efficiently gather energy later on.

Then, when it’s time for them to begin the flowering stage, you should shift their schedule so they receive just 12 hours of sunlight per day. Noticing the longer night (mimicking the change of seasons), the plant takes the signal to shift energy from developing foliage and branches to sprouting buds.

Autoflowering Strains

If you’re growing an autoflowering strain, however, light schedules are a different (and much simpler) story.

See, their name comes from the fact that they don’t rely on light signals to start flowering (unlike photoperiod varieties). Rather, it happens automatically after a few weeks into the vegetative process! Considering that, many growers will leave their autoflowers under the light for 24 hours a day, never turning their lamps off.

However, others argue this is too much for them, and will instead give 18–22 hours of daily light. They do this because plants can get a fair amount of their growing done when they stop taking in energy. Turning off the lights, of course, stops that taking-in process and signals them to focus on growth. This way, plants have enough light to develop impressive results, without your energy bill spiking from constant use.

Don’t Forget to Adjust Your Grow Light

Before we let you go, we want to emphasise again that photoperiod plants will only thrive if they’re on the right light schedule for the vegetative and flowering stages. To assist in that effort, many LED light manufacturers will include a dial, switch, etc. that allows you to switch between modes for each stage.

Along with making that switch, be careful to ensure that you’re raising your lights up in proportion to the vertical height of your plants. The lamps may not generate much heat, but you still want to avoid the risk of burning them.

Other than that, just focus on having a good time!

There are many factors beginners should account for when growing cannabis, and grow lights are one of the most important. Let's help you pick the perfect light.

The Effect Of UV Light On Plants (Black Lights For Weed?)

Last updated June 25, 2019 By Steven 25 Comments

Plants, like humans, are living organisms.

And just like us they require nutrients and the right conditions to flourish. While plants obviously need water to survive, light is their main source of energy.

The natural light we enjoy here on earth comes from the sun, a blazing mass of fire that produces enough energy to maintain all life forms on this planet. The light from the sun is composed of packets of energy called photons; it is this energy that plants utilize to make their food supply.

The light from the sun is made up of varying wavelengths. Plants use most of this spectrum, some colors far more than others, but they do not make use of ultraviolet and infrared light.

Does this mean that UV light has no effect whatsoever on plants?

Quite the opposite. Varying levels of UV light bring about distinct characteristics in crops. Unfortunately, most of them are negative.

First we will cover the effects of UV light on plants in general and then we will cover the effect of UV on cannabis specifically.

How Does UV Light Affect Plants?

Before we get into the effects of UV light on plants, let’s briefly talk about what exactly is meant by ultraviolet light.

What Is UV Light?

Ultraviolet light is invisible to the naked eye and is the shortest wavelength in the spectrum, lying between 100 to 400 nm (nano meters). Before UV light reaches the earth’s surface, most of it is absorbed by the stratosphere.

The earth’s atmosphere is well-adapted to absorb all UV-C radiation, but UV-A and UV-B light still reaches the earth’s surface. Luckily, this light is not too harmful at the levels that reach us.

It is UV-R light that is most damaging to life forms. Thankfully, only 7-9% of it is able to reach the biosphere.

For this reason, under normal conditions, UV light does not have a substantial impact on plant growth. The exact effects of UV light have been evaluated under laboratory conditions, however.

Impact of UV Light on Microbes

Microscopic organisms such as bacteria play an important role in a plant’s life, both good and bad. Some bacteria, such as the ones that cause wilt and rust, may induce diseases in plants. Others, such as the nitrogen-fixing bacteria, may play a vital role in growth and in repairing damage.

Ultraviolet light is detrimental to these microbes and may result in their death. Many scientists have tried using UV light to kill pathogens.

The problem is always the same: while ultraviolet light kills off germs, it also destroys beneficial and symbiotic microbes that play an active role in the healthy growth of a plant.

When UV light kills of these organisms, it causes changes in the composition of materials that the plant needs to make its food supply. For example, ultraviolet light can cause retardation in plants, if it kills of nitrogen-fixing bacteria, because it reduces the amount of usable nitrogen.

Ultraviolet Light Causes DNA Damage

It has been widely documented, that UV-R light is highly damaging to life forms, especially their DNA, lipids and proteins. When DNA is damaged, genetic material retards and either results in mutation or cell apoptosis, where the cell engulfs itself to protect itself from damage.

DNA damage, however, may not always be a negative; mutations in plants are the evolutionary forces that lead to greater diversity and often stronger organisms more suited to surviving.

For example, plants are able to make use of blue light and UV-A to push toward controlled apoptosis. This ensures that nutrients are not wasted and organs that have grown old are eliminated so new organs can be formed.

UV Light Leads to UV-Resistant Crops

With the world heading toward a possible climatic crisis, many researchers have started worrying about the impact of UV light on crops. Considering how thin the ozone layer has become, it is highly likely that in the near future, more DNA-damaging UV radiation will make it through the atmosphere down to the earth’s surface.

This does not necessarily have to be bad news, though. In controlled laboratory experiments, researchers found that crops that were exposed to more UV light actually started producing molecules to block it.

This means that these crops are able to survive in harsher climates and drier regions. Moreover, the plants then used ultraviolet light to their advantage to curb mold and other diseases that were festering in the soil.

This new research might be critical in the future as global warming raises temperatures, the ozone layer is further depleted and more light penetrates down to the earth’s surface.

And, not only did plants become more resistant to harmful light and microbes in those experiments, they also changed their shapes: they became shorter and thicker, which helps reduce water loss.

While UV light is generally harmful to plants, it can still be used to bring about positive effects. A final such effect comes in the growing of cannabis.

UV Light For Growing Marijuana

Ultraviolet light causes the production of resin, and with it THC and CBD, in order to protect the marijuana plant from harmful UV rays. Thus, adding UV light to LED grow lights results in an increase in THC in the resulting buds.

There is no question that at its core, UV light is harmful to plants. But in harming plants, it actually causes them to develop protective mechanisms that make them stronger going forward.

With weed, this results in an increase in THC and CBD. For this reason, feeding your marijuana plants low levels of supplemental UV light will actually help them and generally result in better crops, as is the case with cannabis.

Do Plants Need UV Light?

No, plants do not need UV light. It actually causes them harm. But in causing harm, it forces plants to protect themselves, which can result in a positive for our needs.

Cannabis is the best example. UV light forces it to create more resin to protect itself, which means higher THC and CBD levels. For that reason, many marijuana growers look to add UV light to the final few weeks of the grow, when it has the most effect on the final product.

But what is the best way to give your plants ultraviolet light?

How To Provide UVA/UVB Lights For Plants

A lot of LED grow lights have UV diodes these days, but they only have UV-A light. That’s because UV-B LED diodes are incredibly expensive and are only included on very high priced fixtures.

There is a prevalent belief that only UV-B light is beneficial to THC and CBD production, but this is based on a poorly run study that did not, in fact, prove this. Black Dog LED did their own research and found that UV-A light also increases production of THC and CBD.

For that reason, any LED grow light that has UV diodes will work just fine to give your plants some UV light.

Nevertheless, I know some people will insist their plants need UV-B light. But using LEDs is not the way to do it.

UVB LED Grow Light: Is It Worth It?

Short answer: no.

As mentioned above, UVB diodes are extremely costly.

Fixtures that do include UVB light do so by attaching a UVB fluorescent bulb to their fixture. They are, in essence, an LED grow light with an additional UVB bulb.

And you pay for this addition. There are only two of these lights on the market: the Amare Solar Eclipse 500, which costs $1075 and the California Lightworks SolarSystem 1100 with UVB, which costs $1799.

Personally, I find this a bit gimmicky and it is never worth the increased cost.

Then there is the Cirrus UVB bar. It is the only fixture that uses actual UVB diodes. And it uses only those diodes. It is a pure UVB LED grow light, meaning it functions as supplemental lighting only.

The problem is: it costs $499. For a supplemental light!

Honestly, the benefits from adding UV-B light are not worth paying several hundred (let alone over $1000) dollars.

The only way adding UVB makes financial sense is to get a regular T5 fluorescent fixture and put a T5 fluorescent UVB bulb in it.

These bulbs cost only a little more than a standard fluorescent bulb and they also emit UV-A light, in addition to UV-B.

Here is a good option in two different sizes (these are just the bulbs; you can get any standard T5 fluorescent fixture like this one for them).

How Does Black Light Affect Plant Growth?

Many people ask me about black lights and reptile lights. They want to know if those can be used to supply UV light to their plants.

Black lights emit UV-A light only, so they affect plants the same way any other source of UV-A light does (which was covered above). They are a fairly weak source, however.

Below are answers to the most common questions I get.

Can Plants Grow Under Black Light?

No, most plants can not grow under a black light, if the black light is the only light source. If other light is present, they can grow under the black light, assuming it is not too strong or close to the plants. The black light itself does not do anything to help growth, though.

Do Black Lights Help Plants Grow?

Black lights do not help plants grow. They can help out in the ways described above, as in boosting production of THC and CBD in cannabis, but they do not aid growth at all.

Black Light For Growing Weed?

While a black light will, as mentioned, boost THC and CBD production, it will not grow weed on its own. You can use one as supplemental lighting, but your cannabis plant will not grow without an actual grow light or sunlight.

Do I Need A Black Light In My Grow Room?

No, you do not need a black light in your grow room. If you are growing marijuana, the addition of UV light can boost THC and CBD production, but it is not necessary for plants. If you do add ultraviolet light, it would be better to use a grow bulb like the AgroMax bulbs linked to above, since those emit both UVA and UVB light.

To boost the production of THC and CBD, you would only add ultraviolet light during a specific part of the grow cycle (see next question).

Should I Use A Black Light During Flowering?

If you are adding a black light to your grow for the purposes of boosting the production of CBD and THC, then you’ll want to use that light only during the final few weeks of the flowering stage of growth.

Will Reptile Lights Work For Plants

Reptile lights will work in the same way that black lights or other ultraviolet light will work. They will not help the plant grow, but will activate their defense mechanisms, which leads to, for example, the production of trichomes in marijuana.

The main difference between reptile lights and black lights is that most reptile lights emit UV-B light (there are also UVA reptile lights, but reptiles need UVB more), while black lights emit UV-A light.

Now it’s your turn. Do you have any additional questions concerning ultraviolet light for plants, or specifically for marijuana? If so, please ask them in the comments below and I will be happy to add them to this article.

A lot of indoor growers supplement their grow lighting with UV light, especially for cannabis. Before you do the same, you must know the effects UV light has on plants. It is actually harmful, because…