Should I Leave Weed Grow Lights On For 24 Hours A Day?

As a rule, the most important aspect of growing weed under marijuana grow tent is increasing your yields. In fact, growers are always searching for various methods to improve production.

One of the most often used method for increasing yields is to keep your grow lights on 24/7. However, there are many downfalls to giving a plant to much light.

Actually, many specialists agree that 24 hours of light can keep a plant from efficiently completing the respiration process. Bottom line, if your plants absorb a lot of light, they will be in a constant state of photosynthesis.

In result, too much photosynthesis can lead to damage to the plant and degradation of important plant proteins.

Advantages Of 24/7 Lighting

Keeping your lights on 24/7 has one advantage: it gives your plants more light. More light means faster growth. If you leave your lights on around the clock during vegging, you will see faster growth, without a doubt. But this benefit is outweighed by the disadvantages.

And leaving the lights on around the clock during flowering is not an option at all. Your cannabis plants won’t switch to flowering unless you reduce the lights to 12 hours a day.

If they are already flowering and you increase daylight to 24 hours, you’ll have a disaster on your hands. Your plants will revert back to the vegging stage and it will take forever to get them to re-enter the flowering stage. Never leave your lights on around the clock during flowering.

Disadvantages Of 24 Hour Daylight

The disadvantages of leaving your grow lights on 24 hours outweigh the one advantage. The primary disadvantage is that your plants get no rest period.

No Time To Respire

Sure, you can leave the lights on all the time. Your plants will grow faster. But if you leave them on continuously for many days, your plants will get weaker and weaker. They won’t grow as strong and they will become more susceptible to disease.

Think of it this way. As humans, we can stay up all night without any sleep. We get more done. And we can do it a few days in a row. But the longer we go, the weaker we get. We really need to get some sleep.

Similarly, your plants need their rest.

During the daylight hours, marijuana plants (like all plants) use photosynthesis to convert carbon dioxide and the light from the sun, or from artificial grow lights, into sugars. At the same time, they release oxygen.

And they are also respiring at the same time.

When they are bathed in light, plants mostly photosynthesize, and only respire a little. When in darkness, they halt photosynthesis and focus solely on respiring. They need this to grow properly.

When they respire, they metabolize the sugars created during photosynthesis into energy. They use that energy along with oxygen and nutrients from the soil to power various life processes.

Additional Costs

Running your lights 24/7 costs more money. You need to pay for the electricity to power the lights, and also for the electricity to power fans, air conditioners and any other equipment you might have running in your grow tent. You will also have to change bulbs more often.

Additional Stress On Equipment

Leaving the lights on all night long also means that they, and other equipment, are running constantly, without any breaks. This puts additional stress on them and results in a shorter lifespan.

Additional Heat

Running your lights constantly generates more heat. As mentioned, this means you will also need to run fans and other cooling equipment 24/7. It also means your plants do not get a cooler night time, which is something they naturally expect.

The Best Lighting Schedules For Cannabis

We’ll start with flowering, because there is no flexibility to increase the daylight hours during this stage. Your lights need to be off for 12 hours per day (with the exception of autoflowers, of course). Keeping them on longer can result in your weed plants switching back to vegging and then you’ll have a hard time getting them to flower again.

During vegging, you have much more flexibility. It is perfectly possible to leave the lights on overnight, but as mentioned, it is best to give your plants at least some darkness.

The most common lighting schedule during vegging is 18 hours of light and 6 hours of darkness. This is the schedule we recommend. 20 hours on and 4 hours off works well, too.

Another interesting option is to use a 6/2 lighting schedule. What this means is you leave the lights on for six hours, then turn them off for two. You have 3 of these cycles per day. You still end up with 18 hours of daylight and 6 hours of darkness, but they do not all fall at once.

ECO Farm Digital Timer

Looking at the features of this plug-in timer, you can set the desired time in advance. You will be able to control two outlets at a time.

Another thing that makes this a good product is the small display that makes it easy to monitor the time and to set the desired preferences. Under the screen, the buttons are strategically positioned.

It should be noted, however, that this is rated for indoor use only. An outdoor digital timer should be protected from harsh weather elements, such as rain.

• VERSATILE & CUSTOMIZABLE: Easily set up to 8 on/off programs for the timer’s two grounded outlets. Outlets are controlled simultaneously, and settings can be as short as one minute.
• JUST SET & GO: Choose your own individual days or simply select one of the convenient pre-set combination days. Switch to Daylight Savings mode with a press of a button. Our long-lasting backup battery keeps your settings even in the event of a power outage.
• PROTECT YOUR HOME: Activate the “Random” Vacation mode to randomize your programmed lights. Make your home look “lived in” even when you’re away.
• SAFE & RELIABLE: This timer is UL listed and rigorously controlled for quality and safety.

How Much Light Output Do Plants Need?

Marijuana plants (and any other flowering plants) need 20 to 40 moles of light per day. That is equal to 20,000,000 to 40,000,000 umol (micro moles). The closer you can get to 40 moles, the better, in order to maximize yields.

If you are running your lights for 18 hours per day (see the next section below for more on lighting schedules), those lights need to deliver a PPFD output of 617 umol, in order to add up to 40 moles per day.

When you switch to 12 hours per day of lighting during flowering, that value jumps up to 926 umols, to make up for the 6 hours of lost lighting time per day. That is why you need more lighting power during flowering. It is not a case of your plants actually consuming more light.

Even if you can’t provide that much light, as long as your plants are getting a total of 20 moles per day, they will grow and yield buds. But they will obviously not grow as fast or yield as much.

To achieve a daily total of 20 moles, you need lights that deliver 308 umol during the 18 daylight hours of vegging and 462 umol during the 12 daylight hours of the bloom stage.

Obviously, you can increase the daily total by running the lights for more hours. That is exactly why people run them 24 hours per day. But again, you are much better off increasing the overall light output, by adding more fixtures, or replacing you existing ones with more powerful lights.

Best grow light for indoor marijuana plants

Mars Hydro FC 4800 480W LED Grow Light

Mars Hydro FC 4800 480W LED Grow Light with Samsung LM301B Osram Diodes。 Silent fanless design. No fans zero noise. Built-in large areas of solid aluminum heat sinks, essential for heat dissipation while ensuring long lifespan of the light.

Perfect for 5ft×5ft coverage. Remember to properly adjust the height and brightness accordingly to your plants desired level for optimal growth.

Detachable & dimmable power supply can be mounted remotely on the side of a rack or on an adjacent wall to remove heat from your grow space.

Seperate aluminum heatsink design increase the heat dissipation area, quickly dissipate heat with no noise.

Certificated with DLC & ETL, superior quality components guarantee light safety & lifespan.

Final Thoughts