View Full Version : light timing

05-07-2009, 01:29 PM
I'm finally putting my newly made hydroponic system into action, but I don't know what to do about timing.

If I were to start from seeds, how long do I leave the lights on from the start? Should they remain on 24 hours a day until growth begins, then decrease, or 18 hours on with 6 hours off? What do you recommend?

How long should they stay on once plants get bigger?

05-12-2009, 11:48 AM
24hr -18hr a day light from day1 all the way till flower. then switch to 12on/12off for the entire bloom cycle.

09-09-2009, 05:01 AM
I in my first try at hydroponic growing, nearing the end of Veg. I was advised to do 24 hours of light 24/7 for the entire veg cycle and it's been rather successful. My plants grew fast and very full with 24 hour lighting.

Now I'll see what happens in bloom. As advised there, I'll being doing 12 on / 12 off.

David G.
09-10-2009, 11:54 PM
In my opinion, it's best to veg 18/6. Why?

Plants do most of their feeding at night, especially when the conditions are warm and dry (and most of the grow rooms I have been in have been very warm). Outdoors, when it's hot, plants need to take up as much pure H2O as possible. As soon as the sun goes down and things start to cool down, plants like to have a higher TDS solution, as this is when the rapid transpiration process slows down and feeding really begins. The same can be said for many indoor grow rooms.
It costs more money to run the lights 24/7 (33% more electricity). You quickly reach the point of diminishing returns, as the amount of benefit you may gain by going 24/7 is more than offset by the amount you're going to spend on added electricity.
It's not natural for the plants. I listed this as #3 because it's my weakest argument, and I don't know if there are any published facts to back this up, but think about it. Plants evolved having a light and dark cycle. Going 18/6 is already tweaking things by increasing the day length longer than what normally occurs in nature, but to deprive the plants totally of darkness just doesn't sound right; there has to be some negatives. The only time I believe it is okay to run 24/7 is when the light source is too weak, like when using T12 fluorescents (standard shop lights), as since the light source is so weak, you see some benefit to leaving the lights on longer (the total amount of accumulated light is obviously greater over a 24 hour period than over an 18 hour period). But even then, I usually recommend running the lights 20 hours instead of 18 (or 24) just to give the plants some extra light to make up for the weak light source/lamps.

These are just my own opinions; take 'em or leave 'em. If anyone out there has done any side-by-side comparisons running 18/6 vs. 24/7, please chime in; I for one would be very interested in your findings.

09-12-2009, 11:36 AM
It will also depend upon what you are growing.

Many plants are day-neutral, ie, photoperiod does not affect fruiting/flowering.