What is maximum area that a 1000 watt light fixture will keep plants out of flower in a greenhouse/outdoor environment?

[Chronic Monster]

I have a greenhouse, I would like to extend the veg period on the plants in there.

What is maximum coverage area that a 1000 watt light fixture will keep plants out of flower in your experience?
I know there are different reflectors, led or HID, classis bulbs or double ended, how high the light is hung, etc.

Indoors where my grow light is my only source of lighting I generally do 4'x4' or 5'x5' per 1000, but outdoors I get plenty of sun, only using the lights to extend veg. I want to cover as large of an area possible with as little light as possible as I only have a 400 amp panel.

I did some experiments in the past when growing hemp in a massive GH that had limited power, and I found with a old school magnetic ballast, a 1000 watt HPS and a parabolic reflector I was able to keep plants out of flower at max 20 feet, but some strains of CBD would still flower 15' away, haven't ever experimented with cannabis though, but I assume it's probably strain dependent

I was just curious what some of the farmers on here experiences were?
Thanks for any input brothers.

 

[Holyherb]

I just use string lights to extend the veg period. They have worked well so far. They kept them from flowering during the wild fires in ca till the ash died down. Im using them this year again to help them from going into flower and then revegging since i started my plants indoors with 18/6