WHEN is the best time for supplemental flower-light?

When in your experience is the best time to increase lighting for the flower cycle, before or on the DAY OF switching to 12/12?

I’ve been vegging this round of ladies for almost 4 months.....and it’s time to flower. I veg under 630watt CMH (dual spectrum), then I typically add a vertical 400w HPS open bulb in the middle of my plants on the day I switch to 12/12, and in the past I’ve gotten fantastic, stinky fat buds doing this...additional vertical HPS even fattens the larf (5x5 tent btw)

HOWEVER, a pro grower suggested that the supplemental light be added 2-4 weeks BEFORE flip,and that its critical to stimulate bud sites BEFORE flipping.......trying to find out if there’s any benefit to adding the HPS before flipping? Thx!

No, it won't make a difference.
He is also mistaken. There are no real additional benefit to early supplemental lighting.
Those bud sites will be no more or less active by that idea.

I gotta ask this. So just how do you take 4 months of veg to fill a 5x5?
It should take only 2 months, and that's with topping and lollypopping.
Not only that. In that limited height. You should not need any supplemental lighting to get solid lower bud quality....

Unless your running indoor plants of over 6 ft -7 ft. You shouldn't need supplemental lighting.
Lower buds do not "need supplemental" lighting to form and fill out. They can use some to help ripen them at the same rate as mains.

There are several light threads here that deal with that idea... Use Uncle Ben as a filter in the search.

Thanks for the response Dr. Who; so, I had some Medical Seeds strain “1024” and Jack La Mota as well as Scott R’s Ghost Train Haze outside....i harvested those but took clones and vegged them for almost 4 months to about 4 ft tall and LST’ed. And even though I schwazz at flower then again at 2.5 weeks into flower, I noticed a HUGE difference with that 400w HPS in addition to just the CMH. I’m running 3100K and 4200K mixed CMH bulbs, as I believe in mixed spectrum and massive UVA-B doses, but ended up with larfy lowers and leafy buds before adding in the HPS during flower. I have a great 7inch inline charcoal vent to remove all heat so temps in the 5x5 average 78 on/68 off during my Midwest USA winter.

My first grow of 4 plants in 7 gallon felt pots of FF OF soil yielded a moderate 14 ozs, but next round with the addition of 400w HPS open-vertical caused same strains and setup to yield almost 21 oz total....of rock-hard stinky herb. The mixed spectrum kills in soil, but without HPS medicine is leafy and a bit larfy.

HMM, THANKS FOR THE REPLY..

Sounds like spectrum made a diff. Yet, the lower lighting, applied early enough, may have increased the lowers density.
I do that by stepped harvest.
You simply harvest the upper ripe buds and leave the lowers another 2 weeks to ripen. Same end result just 2 weeks or so more patience required.

It may be a good thing to let plants acclimatize to any environmental changes before entering flower. It usually takes a few days for a plant to acclimatize to higher light intensity.

You also get a window where you can monitor your changes and control that they are actually properly setup by monitoring changes in the plants.