a) why is this in the outdoor thread, the indoor or general growing thread would be more appropriate
b) what causes the plant to flower depends on if the plant is a photoperiod or auto flowering plant.
simply an auto will flower when it is mature and ready to do so even if the plant is running under 24hr of light the plant will still flower when its mature
a photoperiod plant will flower when the amount of light it receives in a day is less than or equal to 12 hrs.
the spectrum or colour of the light isn't what causes the plant to flower. outside in the real world when the days are longer there is more light from the blue spectrum and when the days are shorter there is more light from the red spectrum and has to do with the angle that the sun hits our atmosphere at. inside many growers will try to match their light spectrum to what nature would naturally provide outside (more blue in veg more red in flower) although this isn't necessary, there are many growers who only veg under hps lights which mainly throw off light in the red spectrum and im sure there has been a grower who has flowered under nothing but a mh before, while not optimal it will work.
im sure someone with more knowledge on lights and light spectrum's will be able to outline the pros amd cons of using each spectrum in any stage.
Wrong.
the circadian rhythm is what causes plants to flower.
It is a genetically stored hormonal reaction that the pigments in the tissue of the plants releases when a concentration of the R-FR spectrums Flare out within a cycle that indicates to the plant its growing season is coming to a close.
Cryptochromes- and Phytochromes react directly to both the red and blue spectrum's of light independently.
The rhuderalis strains you are referring to that flower under 24 hrs of light are indigenous to tropical equitorial zones that do not adhere to the same climate and lighting conditions as the strains that developed in the southern and northern hemispheres. These plants actually do not have phytochromes, which is why they flower automatically.
It also is not so regulated by 12/12 as everyone would say. But as a general rule of thumb- it works. Full spectrum bulbs contain a dense enough amount of the F-FR spectrum to induce flowering, HPS has much more FR density which helps the plant regulate its hormonal balance with a focus on fruit production- so yes you were correct about the "light angles changing" what is actually changing is the part of our atmosphere that the radiation enters from blocks less FR spectrum, and its increased density triggers a hormonal reaction in the plant to begin flowering.
The natural light schedule decrease signals colder weather and uninhabitable conditions (also measured by the same pigments) which causes the plant to put all of its energy into reproductive processes before the days are too short and cold to be inhabitable.
That link discusses mostly Auxins- and unless you actually understand that Auxin is many hormones that do different things reacting to environmental stimulus, its pretty much useless in actually understanding what causes flowering.
Never try to chemically induce flowering in a plant that you want to see a smokable harvest from.
We have the exact same pigments in our skin that do the exact same things- reacts to light change and signals a hormonal response in our bodies.
so- Circadian rhythm is what actually causes flowering to start and regulates its progress.
Marijuana is deciduous- The primary difference between indica and sativa is the zones they originated in and became indigenous to. One (sativa- came from the shrub/tree zone) the other (indica the herb zone).
When lighting changes- back to signalling the plants hormones that a growth season is present or coming- it will reveg.
thanks