ok no where in the hell when growing outside where the cannabis plant is derived from do we have 18 hrs or 24 hrs of light why should i when growing indoors use these light cycles?
Well I should point out that the majority of strains that exist today have been so genetically altered or bred for certain favorable traits that if left to grow wild outdoor in their natural environment would likely not survive.
Not to mention that indoor you are attempting to produce an ideal growing environment with little room for deviation and in return get a quality that an unattended outdoor plant could not obtain.
So that being said, yes indoors its done a little differently than mother nature would have it but thats why the pot is so much better.
you are trying to replecate the same amount of light in an outdoor season(6 months +/- depending on where you live) into 90 days +/-indoors.
Add this on top of everything I just mentioned and I think you have a perfect answer to your question.