The different spectrum may be better for flowering, but it the length of day that determines flowering.

I'm not sure about sunflowers.

Some plants simply flower after they reach a certain size no matter what you do. Some flower at a certain day length. Others flower at certain temperatures.

Most of the information you've probably read relates to a certain plant that isn't legal in most places - specifically the lower color temperature light and 12/12 light/dark cycles. Of course that does work with certain other plants as well.

Other plants will bolt to seed if they get too hot. I know that broccoli is one of those. That's the main reason it isn't grown in the summer - it doesn't grow big, it just grows seeds. I'm not sure what triggers the early-flowering stuff like the stuff you see in flower gardens early in the spring. If they're triggered by light it'd have to be the lengthening day that makes them bloom rather than 12/12.