OK, here’s my thoughts on this…
There is only one sun. Although during the sunset or in the winter, as the light is angled through and filtered through more atmosphere, it does become a little redder in appearance, the actual difference of the relevant spectrum that plant’s leaves can use is so minimal that it is actually unimportant.
There may be some truth the plant finishes faster with more red as it thinks it is winter and needs to hurry up and finish, but there is very little evidence of shorter flowering time with more red light vs. blue light.
It used to be when using incandescent lights for growing indoors, the problem was the plants would most often get sick because of not getting enough light from the blue end of the spectrum. You’ll notice most “professional” florescent plant lights come with a 6500k light. You can flower under these lights without any problems and they are considered cool or blue white light. However they actually have plenty of red light in them but as it mixes with the other colors we just see it as white light. A perfect mix of red, blue and green light makes white light.
The truth is plants respond to lights of varying colors because there are several different plant pigments which are capable of absorbing light and transferring the energy to chlorophyll which catalyzes photosynthesis. Plants may grow in green light, but efficiency in the use of the total light energy will be small because plant absorption of green light is very small.
As is well known, plants will grow best if given a mixture of blue 450 nm light and red 650 nm light (a ratio of bout 20%-30% blue and the remaining LEDs red, seems to be best – I actually like to mix in some pure white LEDs, the equivalent of 5000K-6500K white color rating). BTW, 5800K is supposed to be the light color of high noon. This white color rating has some photosyntheticly active green and yellow/orange spectrum – as well as the blue and red spectrums. And as an added benefit – your plant appears a more normal green, if you have enough of the white LEDs mixed in, similar to the appearance under HPS or MH and it seems a little less stressing on the eyes and makes it easier to read the plant’s health by the color of the leaves.
Plants grown in all red light will grow to be overly tall and leggy and ones grown under all blue light may be low-growing and stocky. Overall, red light is more important and efficient in photosynthesis.
So does more blue equal more vegetative growth and more red equal better flowering? No, if the minimum amount is available then more of only one spectrum is not necessarily better. For example if 20% blue keeps the inter-nodes short during veg, twice as much blue will not make even shorter nodes. In the same way increasing the amount of red required for flowering will not necessarily equal bigger flowers. Overall intensity/lumens/LUX, up to a certain point, is what makes for more intense growth. But of course, for those that don’t know, there is such a thing as too much light and it will cause photoinhibition.
So why do people use MH that seems to have more blue light in vegetative growth and HPS that seems to have more red light for flowering?
HPS spectrum is not as well balanced, but it has the highest radiant flux density of any man-made light source (with the exception of newer high output LEDs which may have a better spectrum specific flux density and better photonic flux, and induction plasma which may have overall better radiant flux with a more balanced spectrum). And MH has a more complete and balanced spectrum but doesn’t have as high of radiant flux and as a result has less penetration and lumens per watt.
As florescent and MH have more blue light and not as intense of light is required for veg, this is why florescent and MH are used for veg, and as flowering tight nugs requires intensity and penetration and blue light is not as important for flower, HPS is preferable – and has enough of blue to prevent growth dysfunction.
So I would imagine intense balanced blue and red light through the entire life cycle is best and as such I’d probably run both on, through the entire life cycle. A proper ratio is probably best for the entire life cycle. And at the very least I certainly would be running the full spectrum/maximum lumens/intensity pretty much all through flower and right up until the very end.
