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A lot of people assume that leaving your grow lights on for a full 24 hours makes sense, surely having the grow lights on all the time will simply lead to more growth, and then you will end up with more yield?
But of course not everyone thinks this way, and there is debate around whether this is a healthy practice for growing different plants.
There is common belief that leaving the lights on will lead to faster results, but some people think that it might hurt your overall yield in the end.
This question unfortunately does not have a black and white answer, and your approach to the lighting for your plants should rely on a few different factors to ensure that you get the best results!
If you are running your grow lights for the full 24/7 cycle, then your plants will of course be getting as much light as possible. This is the simple solution if you think that your plants are not getting enough light throughout the day.
However, if this is the case, there are some more effective ways to fix the issue than leaving the lights on 24/7, for example you could get more powerful grow lights, or more grow lights, instead of having them continuously on.
The best way to evaluate if leaving your grow lights on 24/7 is a good idea is to look at the pros and cons so you can weigh these and use this to help you come to a conclusion.
So, if you have any questions about leaving lights on or off when growing plants, keep reading to get the information you need!
Advantages Of 24/7 Lighting
As we mentioned in the introduction, the main advantage to keeping your lighting on 24/7 is that your plants will get more light.
Other than this the only other potential advantage is that you will not need to bother with lighting timers, but other than this there is not much else.
However, we know that having more light will lead to faster growth, so is this worth it?
By having your lights on while the plants are vegging, you will witness the growth getting noticeably faster.
You will see that the plants are growing buds at a much faster pace, however, the disadvantages to doing this, we believe, outweigh the benefits.
If you are working with cannabis, then leaving the lights on 24/7 while the plant is flowering will not lead to great results, and you will want to switch to only 12 hours a day if you want to see good results with your cannabis flowering.
If the cannabis has started flowering, and the light is on 24/7, you will essentially revert the plants into their vegging state, and this will make it so they take far too long to get back into flowering.
So, unless you want the plant to go back to vegging, after flowering, which is unlikely, do not leave the lights on 24/7.
Disadvantages Of 24/7 Lighting
There are actually quite a few disadvantages to leaving the lighting on 24/7 and we believe that this heavily outweighs any potential positives which your plants could experience by leaving the lighting on for 24 hours.
We will go through these disadvantages now!
No Time To Respire
While your plants will grow faster, they will essentially give them no time to respire and no time to rest.
So if you are leaving the lighting on 24/7 for days and days with no time to rest, the plant will start to become weaker and weaker.
By making your plant weaker, they will not grow to be as strong, and they will be noticeably more susceptible to any diseases which may come its way.
Think of your plants like humans, if we are staying up throughout the whole night without sleep, in theory we will be able to get way more done with the active hours.
However, the longer this is done, we will get weaker and weaker, and less and less efficient, and the work we are doing will get lower and lower quality.
We understand that humans need this, and the quality of your plants will show that they need it too!
For example, during the daytime in light, a marijuana plant will be using photosynthesis to convert any CO2 present using the sunlight or grow lights, into sugars as well as oxygen, this is the plant respiring.
So, when a plant is surrounded by light, it is likely to be photosynthesizing, but usually not respiring as much.
If they are respiring they will be metabolizing their sugars which they have made during photosynthesis and then these will be turned into valuable energy for them.
By using this energy with nutrients from soil, and oxygen, they can power different life processes.
This is a more practical reason, but you will definitely need to keep it in mind if you are on a budget, but keeping your lighting on 24/7 will simply be a higher cost for you.
You will not just be paying for the lights, but also for the ventilation fans and air conditioners you will have running. You will also be paying the extra cost for replacing bulbs often as well.
Additional Stress On Equipment
This leads on from the previous point, but you will be putting a lot more stress on the equipment which you already have. All of your equipment will be running with essentially no breaks.
This means that your equipment will end up not lasting as long, and you will be stuck with the cost of replacing this more often as well!
One of the other main disadvantages of having lights on 24/7 is that your lights will of course generate excess heat, and with no downtime, the lights will have no time to cool off.
This means that any cooling equipment you have will need to be running more effectively which will cost you a lot more.
This is because the plants are expecting a cooler nighttime, which of course they will not get if the lights are on 24/7.
The Best Way To Get Extra Light
So, if you want your plants to be getting more light, but you are unsure what the best way to do this is, there are some other methods you can use to get this!
For example, you might want to buy new grow lights to ensure that they are working as efficiently as possible. You can either replace the old ones, or get new ones to work alongside them.
Sometimes you may not have enough light for your plants to grow properly while they are vegging, then they will not have enough to get through flowering.
If this is the case, then you should definitely be investing in more lights. If you try to use your lights 24/7 to fix this, all you will impact is the health of the plant, so getting additional lights, or fixing other ones is a much better method.
How Much Light Will Your Plants Need?
For a marijuana plant, when they are flowering, they will need between 20 and 40 moles of light every day, or 20 million to 40 million umol. You want to be getting as close to 40 moles as possible to get the best yield possible.
For example, if you are keeping your lights on for around 18 hours daily, you will want your lights to have a PPFD output of 617 umol to get the 40 moles every day.
Or, during flowering, you could have them on for 12 hours daily, and then you will need 926 umol instead to get the right amount.
You want to balance the time with the lights on with the right umol to ensure that you get the best results from your yield.
You obviously do not need to get 40 for the plants to grow properly, but you will want them to get at least 20 for good results.
Best Lighting Schedule For Growing Cannabis
The best place to start with this is the flowering period since there is no option to increase light hours with only 12 being the maximum, unless you are working with autoflowers.
You do not want to keep the lights on any longer than this because then they will revert to the vegging state and then they will struggle to get back to flowering which is a massive hassle.
However, when your plants are vegging, you have much more flexibility, so one of the more common schedules would be to have 18 hours of light and then 6 hours dark, however some people even go up to 20 hours with only 4 dark.
Some people also use the 6/2 method which is essentially the 18/6 method but you have 6 hours light and then 2 dark, 3 times a day.
Will Autoflowering Plants Require A Dark Period?
Your autoflowering marijuana plants will still need nutrients and it will still need proper time to rest. These strains will switch to flowering automatically and you do not need to switch your daylight hours to achieve this.
You could theoretically run the lighting 24/7 for these, but it will still affect the quality and will cost you a lot more in the long run.
Will Seedlings Require 24 Hours Of Light?
Your seedlings should not be 24/7 light and they too need a dark period, for these we would recommend a 16/8 schedule for lighting.
Hopefully this article has informed you on why leaving growing lights on 24/7 is definitely not recommended for any plants!
I’m an avid gardener and cannabis enthusiast. You can usually find me in my garden caring for my plants or at my computer crafting helpful blogs for my readers.