Thread: a question on lighting

what's a good lighting schedule for the plant?

24 hours a day during veg, then 12 hours a day during flowering. If you don't want your plants to grow too fast, you can use 18/6 during veg too.

theres two schools of thought on this topic,

the only difference in my shedule is i use 18 hours of light and 6 hours of dark during veg, it just seems more logical.


one theory being that 24hrs during veg gives the plants a lot more light, and hence quicker growth.

the other bieng that 18 hours is closer to a natural cycle and uses less power, also giving the plants "downtime" for growth/recovery.

are there any "more scientific" arguments that suggest one or the other that anyone knows of?

18/6 for veg
12/12 flowering

the reason you don't wanna go 24 hours during veg is because the plant needs those 6 hours of darkness to carry out other processes. it hear tha 24/0 just stresses the plant.

how long should you veg the plants after they've sprouted?

I think you should try to veg for 6 weeks.

It's beneficial for the plant...and allows it the opportunity to show pre sex characteristics. Plus...it seems too many people rush their plants. It also depends on what you hope to acheive.

You should also give the sprouts a week or two to grow and establish a root system before you consider them to be in the "veg" state.

From Greg Green's "The Cannabis Grow Bible" (which is also backed up by personal experience):

"Cannabis is a light demanding plant. Professional growers keep the light on their plants using the 24/0 photoperiod for this reason. Plants that grow under 24/0 flourish and do not need a quantity of darkness in order to rest and perform photosynthesis properly. Plants that are grown in optimal conditions under the 24/0 light regime grow vigorously and the benefits of the 24/0 photoperiod can be seen actively in the results. More nodes are formed, more branches are created, leaf numbers increase, the plant is growing at its finest.

Some growers opt to use 18/6 as their photoperiod. Under these conditions the plant will grow quite naturally but not as vigourously as the 24/0 photoperiod.

The 18/6 photperiod expels 3/4 the amount of light that a 24/0 photoperiod does. Although this does not mean that a plant produces 1/4 less leaves, branches and nodes under the 18/6 photoperiod, it certainly does show the correlation between light and cannabis growth. There are no problems associated with 24/0 and although some have attributed cannabis sexual dysfunction (the hermaphprodite condition) to the 18/6 photoperiod these problems are actually the result of heat stress. (I think he meant 24/0 for this part, actually.)

A 24/0 photoperiod requires that your grow room temperature be kept well monitored. The 18/6 option is cheaper to run. You use a quarter less electricity and this will have an impact on your electricity bill. Also the 18/6 photoperiod will generally extend the bulb's lifespan. During the 6 hours of darkness the grow room is allowed to cool down for this period but a well maintained grow room setup should not require a cooling down period.

24/0 and 18/6 both share the same problem though. Once you start the photoperiod you should keep it that way especially when the plants near maturity -- the pre-flowering phase. An irregular photoperiod can cause more males than females to develop. It can also cause sexual dysfunction to appear. Whether you choose 24/0 or 18/6 as your vegetative photoperiod try to keep that photoperiod until your plants are mature enough to express their sex."

Now, what I did once as a test was veg some plants under 24/0 and some under 18/6 (I have two veg cabinets, which made this easy to try). After three weeks, the difference was significant - the 24/0 plants were quite a bit bigger and more lush than the 18/6 plants. Very noticeable. This is why I said 24/0 for veg, or 18/6 if you want them to grow slower (but at a cheaper cost per day, electricity-wise). Sometimes you NEED them to grow slower, because your flowering space won't be ready for a while, and that's when 18/6 seems to be most useful.

Of course, your mileage may vary. And feel free to try that experiment yourself. I assure you that if you do you will see a difference, and the 24/0 plants will be significantly larger and more developed than 18/6 plants, if both are the same strain (or, even better, clones of the same plant), and vegged for the same number of days. And if you need a cooling-down period because your grow room/cab gets too hot, obviously YOU might need that 18/6 photoperiod, even if the plant doesn't. But the most important thing is that you keep the same photoperiod the whole time during veg, whichever one you decide to use.