Thanks for the response. Well my backyard is not that big hence it does light up the entire backyard.
So it is always good to provide some darkness to plants?
some types of plants want a dark period while others could be grown under 24/7 intense lighting conditions.
I expect that your outdoor lighting isn't going to provide the same lighting to the plants as what is used for indoor growing though and expect for most purposes, the veggies will take night time even with the yard lighting as a dormant period and still do fine.
more light doesn't mean more growth. Think of nature. As the growing season continues thru the summer the days are gettng shorter and dark period longer. Alot of growth appears during the night cycle. Pick up a botany book and it explains it all very well. There are short day plants and long day plants. All 24/hrs of light does is make the power company more money and costs you more money in buying more light bulbs that burn out quicker.
More light does equal more growth. Short day/long day/day neutral is only relevant to the plant switching into its reproductive phase and has nothing to do with how a plant responds to light during it's vegetative (or main growing)phase.
Though I have yet to read a study that shows there is any major benefit to growth beyond an 18-20 hour light cycle. I've had many plants grow just as well on a 24 hour light regimen as on 18-20 hours of light.
A lot of growth really doesn't occur at night, not counting things like sorghum, or circadian clock confers as they are not typically found in gardens or AP systems :). These plants have developed a strategy for maximizing growth in a highly competitive environment.
Some stem elongation will occur just before dawn in some plant sprouts, but again that is not growth that would not have happened had the plant been under 24 hour light. Again this only refers to plant growth cycles, not flowering or setting fruit which is a whole 'nother ball game.
Bolting in lettuce is dependent on interactions of both light and heat as well as genetics (which may be most important aspect of all). The gene that determines a predisposition to delay bolting can be bred into a cultivar, luckily for us. Many with these 'slow bolting' traits. Some are slower than others...
Teh, how old were the lettuce plants? Maybe it was just time, and warm enough? I agree with TC, unless you have like a 1000Watt HPS lamp for a porch light, it probably wasn't the culprit.
Plants and their stomata, it seems, have to constantly respond to changing conditions during the day (humidity, CO2 concentrations, light intensity). Their opening and closing are dependent on many things. Scientists seem to have the mechanisms down as to how this happens, but even in 2012 they are not at all sure how the stoma's "guard cells" (which allow opening and closing to happen) exactly works, and it's still quite a controversial issue. (If your a plant geek.)
And no, it probably doesn't matter, unless your a plant (or above mentioned geek :) ...I just don't agree that ..."a lot of growth occurs during the night cycle..." or that 18-24 hour light is harmful. Might not be worth the electric bill beyond 18 hours, but not necessarily bad.
Could you please send a link to that particular study that shows that light was causing "random" opening/closing of stomata irregardless of other conditions (CO2, humidity)?
Personally I think you are wasting your time using more than 10 to 12 hours of light. I know that these are veggies but I would like to share a little experience. I have ran experimetns with cannabis and I do not follow the normal schedule. I try to tell other people about different light schedules and they will not listen at all. I also know that everyone who says I am wrong has not tried to experiment. Until you personally have ran an experiement with the same conditions only for different light cycles then I will continue my 10 to 12 hours of light. Tell me where on earth you would get more sunlight than this other than the extreme North and South. You would need two suns to get that amount of light. Don't try to beat nature, its been doing it for much longer than we have.
There is an old technique called the gas lantern trick. To keep some plants in a vegetative state, old gardeners use to turn a gas lamp on for about an hour to prevent budding. During the night, cannabis at least, builds up floral hormones. The one hour of light in the middle of the darkness period will prevent them from going into budding. Light intervals have alot to do with plant growth. Run the experiment and then make a decision.
Go for it. Seriously. I'm not trying to change what you do. All I'm saying are two things
1) 24 hour light cycles are not "harmful" (as I've already stated, not worth it, and not much benifit beyond 18h, 16, or 20 depending on the cultivar, but that still does not mean that it is harmful).
2) I do not believe that significant growth occurs during night cycles. That's it.
If you can get monsterous growth from your cannabis using a flat all 10 hour lighting schedule, that's great, and by all means continue. It still doesn't mean that they're doing most of their veg growth at night. Or that 24 hours light cycle is harmful for veg stage.
And yes, over the last almost couple of decades now, I generally have a number of different systems running at any given time, more or less. I too like to experiment, and/or test out what I've read or been told.
Interruption of an otherwise long night by light (particularly in the red 660nm range) is a well documented and good way to prevent flowering of many plants, including cannabis. Since saying that a plant is "short day" or "long day" is a bit misleading. "Long night" or "short night" better describes the mechanism at work, and if you interrupt that dark, your right it totally messes them up. A little like hitting 're-set' ;)
I don't think that we should 'try to beat nature', but I do not feel that we should mystify nature either.