Advantages of "Night Growing" in tents

I have mine set to be “Lights On” only at night for several reasons

  1. In winter, the coldest time is at night, and the heat from the grow lights (LED) keeps the tent warm
  2. In summer - it is easier to keep the heat DOWN at night

But there is a third factor that comes into play, and it is Relative Humidity (RH). At night, with cooler temperatures, the RH is higher than in the daytime. Also - when my cooling fan is running it drives the moist air that I run an Inkbird controlled humidifier to create out of the tent so that the humidifier has to work harder to keep it in range.

Have a look at this chart:

Someone here posted that, and it gives us a very good idea where we want the humidity to be at different temperatures. As you study it, you notice that at higher temperatures the RH has to increase as well. It also seems to me that around 75 f. (roughly 20 C.) is the ideal, and it is also fairly do-able inside a house or apartment without breaking the bank on air conditioning running up the power bill.

But at that temperature the ideal is between 55% to 65% RH.
70 degrees f. is five percent lower, and much easier on the humidifier. It’s refilling the humidifier with gallon after gallon of water that gets to be annoying.

Now let’s have a look at this:

On the upper right of that weather site, you can select Humidity as what you want to look at
using the time slider on the bottom of the display you can look at changes throughout a 24 hour period for days ahead, and see what the humidity does overnight, and also temperature

What I have found is that if my lights are OFF between the hours of 9AM and 6PM the natural humidity is closest to what I want it to be. That is of course a 15 hour “Lights On” period - it can be extended to 16 or 18 hours if you like, but that is the ideal time frame to make the most of cooling and ambient air humidity

When the lights are off during the day, the cooling fan as I have it set up (the vent fan is controlled by an Inkbird Temperature Controller) seldom comes on at all. I may need to add one more vent fan because the other thing that happens is with the lights off during the day I have seen the RH in the grow tent rise well over 80% at times

That can be corrected by connecting a second vent fan to the “De-Humidifying” connection on the Inkbird RH controller, which has one connection for a humidifier and another for a DE-humidifier

Venting off the excess humidity with a fan is all I need to do, there is no need to dump huge cash into a complicated and expensive Dehumidifying machine

But this is the setup that I am running with now and enjoying huge success! The plants love it. I keep a gallon and a half pump sprayer in the tent for emergencies, or when in the Vegetative stage I want to mist my plants frequently.

Just now I have a four foot by eight foot tent, 80 inches tall, and 4500 Watts (equivalent) Morsen LED arrays supplying light energy so the heat given off is considerable

What it comes down to, Lads and Lasses, is a balancing act. But by running everything at the best time of day (or in this case NIGHT) it is much more manageable…


What I think I want to reset everything to is 10AM to 4:30PM for Lights Out

That will give me 17 1/2 hours of lights on

Anoth added bonus of running lights at night is that it is cheaper hydro during those hours aswell :hugs:


9:00 AM to 5:00 PM is when peak power consumption takes place from toasters to industrial demand, including solar farm fluctuation and soar winds from the sun. At night the power runs steady and true without spikes and drops in voltage, therefore sensitive electronics take less of a hit running at night when all things that effect voltage are for the most part sleeping. Electric smelters on the grid are not withstanding, they run at night too and use as much power as a city offsetting demand, power companies offer insensitive for them to run at night when demand is down and the grid can handle the load more efficiently.
Another thing to consider is checking your voltage at the socket to make sure your transformer at the pole is not damaged or burning out, you should be getting a reading of 120 VAC minimum without anything running on that particular circuit. Also check both legs 240 VAC.

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Our peak hours in Ontario are from 7am to 7pm. Night time is off peak

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All good points!

~ and many areas pro-rate power during certain months, so any savings at all is a bonus.

In the summer months especially, people run A/C units so much during the day that brown outs are common in some areas. During the winter most people use natural gas for heating so the effects are not parallel. As springtime began right about one week ago exactly, the hot weather and A/C usage demand will certainly be on the rise, and this I think is also looked at by power companies in terms of off-peak users.

It’s a good move to look into whatever and however we can insulate using window film, check weather strip around doors, and whatever else we can do to make our homes more energy efficient anyhow - but the side benefit that it helps offset the cost of growlighting I reckon we need not expect to hear any public service announcements regarding… :rofl:

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I’ve also been thinking that there may be a fairly simple way to set up an “Intercooler” that runs cooling air in one side of the tent and out the other, or by using a waterline system with a small radiator and a fan so that both humidity and CO2 can be maintained without venting any of it out of the enclosure. But I have no need to get that intricate just yet

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I am now running my lights on from 6pm to 6am with spring and summer coming up. Winter I run the opposite