Best Time To Run Grow Lights (And Why There Is So Much Debate)

Let me guess.

You’ve read a number of opinions arguing vociferously for running your grow lights at night.

And a number of other opinions arguing just as strongly for sticking to a natural light cycle.

That’s how it is with every aspect of growing marijuana indoors, unfortunately.

So when is the best time to run grow lights?

Honestly, the answer is that it depends.

I tend to fall on the side of sticking to a natural grow cycle, because I feel the advantages outweigh the disadvantages.

But this is not always the case. There are situations, where it makes more sense to run the grow lights at night, for example.

Keep reading for a full discussion on the best times to run your grow lights. In a few minutes, you should ae a clear idea what is right for you and your grow.

 

Best Time To Run Grow Lights

The best time of day to run grow lights is during normal daytime hours, mimicking the sun. There is no reason you can’t run them at other times, but daytime has more advantages than other times.

Cannabis, like all natural plants grows naturally outdoors in the earth’s soil and gets life from the sun’s powerful rays. Thousands of years of evolution have resulted in cannabis plants reacting to sunlight and darkness in ways that benefit the plant.

 

Reasons To Run Grow Light On The Natural Light Cycle

Most of the reasons to run grow lights on the natural light cycle have to do with it being what plants are used to. And also what you as the grower, are used to.

 

In-Line With Nature

Running your grow lights in line with the natural light schedule of our planet is just good common sense. In this way, you are not making the plant change what it is already used to, which allows it to grow unimpeded.

 

Good For Transplantation

Many growers start their plants indoors for germination and early veg stages, then transplant them outdoors for the next growth phase. In this situation, having your plants already on the natural light cycle of the earth pays off nicely. It ensures a smooth transition from an indoor to an outdoor grow environment.

 

Easier For Humans

The natural light cycle is also easier on you, the grower. The plants go to sleep when you go to sleep, and are awake and get light when you are up and working. Having your sleep schedule in line with your plants is just easier all around, and good for you and the plants.

That said, just because running your lights during normal daylight hours has several advantages and is usually the best time to run them,that does not mean it is the only time that will work, or that it is always the best way to do it.

 

Running Grow Lights At Other Times

The truth is, you can run your lights whenever you want. There can be advantages to running them at different times from the natural light cycle. For example, if you live in a hot climate, running you lights at night could help keep down grow room temperatures.

The key is to keep it consistent. For example, if you run them from 10 pm to 10 am on Monday, do not run them from 6 pm to 6 am on Tuesday. Stick to the same exact schedule every single day, just like the sun does.

If you want to run your lights all night long and shut them off at 5 am, that is perfectly fine. Just remember to do it the same every day. Varying a little bit can actually trigger your plants to go into different growth phases or even stun or shock them. Keep it consistent no matter what time you run your lights!

 

Can you Leave Grow Lights on for 24 Hours A Day?

Although it may sound logical, since light makes cannabis plants grow, it is actually not a great idea to leave your plant lights on 24 hours a day.

Plants need a resting period just like people do. They will grow fine with 24 hours of light per day, but they do better with at least a few hours of rest. It also gives your grow room a chance to cool down. That is why we recommend giving your plants a dark period.

Of course, this is only an option in the vegetative stage. During flowering, plants need 12 hours of darkness per day. But again 24 hours of light is unnecessary and not really worth it. That said, this is an area of debate.

 

Differing Opinions On 24-Hour Lights

Just like almost anything, there are differing opinions regarding 24-hour lights for cannabis (or just how long you should leave grow lights on in general). Those who are in favor say that it helps your plants get through the veg stage faster.

Those who oppose it say that it is bad for your plants and puts unnecessary stress on them, with the only benefit being that they reach the flowering stage a little bit sooner.

You will have to decide for yourself if having your lights on for 24 hours is good for your grow. We say it’s a bad idea, but we are just one voice in a sea of arguing growers.

 

How Long Should You Leave The Lights On Every Day?

Just like with the 24-hour lighting argument, there are many different opinions here. In order to keep it simple I will just reiterate what the most commonly accepted answers are. Most growers tend to land somewhere around the 16-8 or 18-6 mark during vegging.

This means 18 hours of light per day and six hours of darkness. The first number is the number of hours of light and the second one is darkness (16 light-8 dark, for example).

To begin the flowering stage, you then need to switch the lighting schedule from whatever you chose for vegging to a 12-12 schedule. There is no debate here. During bloom, marijuana plants need 12 hours per day of light and 12 hours per day of darkness.

 

Variations Are Common

As mentioned some growers will do 16 hours of light and 8 hours of darkness, others will do 18-6, and others will do 20-4. You just can’t go down to 12-12, since that will signal your plants to begin flowering.

Basically, the lighting schedule a grower chooses during vegging just depends on who they listen to, or what their past experiences are. Of course most growers tend to be quite superstitious, meaning they will stick to what has worked for them before (and often argue vigorously against any other option, without ever having tried it themselves).

If you have ever seen a baseball game where the pitcher does a little move every time before he pitches, it is the same with growers. They can be very prone to superstitions, and they do not like to change what they know works.

 

Natural Sunlight Outdoors Vs Artificial Grow Lights

There is no real agreement on this. A common opinion is that sunlight is better than grow lights. But the best modern LED grow lights give you a spectrum very similar to the sun and growing indoors has many other advantages (the most important being that you control the climate). Learn more about how grow lights work here.

As mentioned earlier, cannabis has been evolving in nature for thousands of years and it is quite accustomed to the sun and how it works in nature. The sun has the perfect balance of light for cannabis or other plants.

Of course, some say man-made lighting is better because it can be customized to work better for each strain, or growth stage or what have you.

There may be some truth to this, but as of yet, nothing has been proven. In the end, plants do well under both sunlight and good quality grow lights.

But, as mentioned, outdoor plants experience more adversity like bugs, bad weather, floods, pests, and more. As a result, indoor plants are better off, assuming you provide them the right conditions. Of course, this has nothing to do with the sunlight.

 

Best Time Of Day To Run Grow Lights: Final Thoughts

For most growers, the best time to run grow lights is during the daytime, following the natural light cycle of mother nature. That is what plants (and us growers) are used to, meaning it is easiest on everyone.

However, there are also instances where it make more sense to run the lights at night. The best example is if you live in a hot climate. Running your grow lights at night makes it easier to keep your grow room cool. This could end up saving you quite a bit of money.