If you want to get the most from each plant using 250-watt lights two plants per lights works best. If they are just normal width plants and you don’t want them jammed together so tight that light cannot penetrate, more than two plants (flowering/adults) is pushing it.
　
When I started with a 250-watt HID light I used a space that was roughly 4 ½’ X 3 ½’, so like 15 ¾ sq. ft. I only planned on growing four plants and I was sure that a 3ft. X 3ft. footprint giving me nine square feet would handle it. Not half way through the first grow’s flower stage I had purchased a second 250-watt light.
Of course later I wished I had just scrapped the first 250-watt light and bought one 400-watt light but anyway, two good sized plants under one 250-watt light will get the most you can get out of a 250-watt light without going to the extreme of purchasing one for each plant.
　
To get the most from a 250-watt light you need to keep it close to the tops of your plants, as close as you can without cooking them … and that includes keeping a fan blowing on the bulbs and just the tips of the plants whenever the lights are on … just to get that little bit closer.
　
When you do that the footprint gets smaller so it is hard to get enough light to the outer portions of your plants, or to the jammed inner portions if you do that to try to keep them all closer under the light.
40% of a plant’s production comes from the outer portions so if you cannot supply it with enough light, there will be little to no production on the sides and farther down the plant.
　
The one thing you do have going for you when it comes to using 250-watt lights is your actual usable height to grow in will be limited enough that you will not be able to veg your plants long enough for them to outgrow the combined lighting capabilities of your lights and reflective material.
　
You said the height of the area you have to grow in is 5ft. Well when you subtract from that the height of your pots and then subtract from that the minimum number of inches your lights/reflective hoods will need when raised as close to the ceiling as they can go and then you subtract the minimum amount of distance that you will have to maintain between your lights and the tops of your plants so you do not damage them and what is left is your actual height to grow in. A rough guesstimate tells me that if you veg to a height that would not let your plants ourgrow your lighting capabilities your plants should pretty much fill your usable growing height.
　
Well if you do the two plants per light you could get away with 5-gallon pots, maybe even 4-gallon but I would only take them if I needed some now and could not find what I wanted. The area you hope to use, assuming that you want to use as much of the entire floorspace as possible, is 3ft by 5ft, a total of 15 sq. ft. They say a 250-watt light will cover an area 3ft. by 3ft., which it sort of will, but if you keep it lower at all times to get the most out of it the footprint is smaller at all times than you might expect.
　
Using the standard 3ft. by 3ft. two 250-watt lights would cover the square footage, two would give you 18 sq. ft. of light coverage. But because of the shape of your space it wouldn’t work out very well. If you positioned them so they split the area into three sections with more plants on either side of them you will not get really good light to many areas of some plants.
　
If you use three 250-watt lights, hanging them so they are lengthwise across your 3ft. span and then cut the area into four areas you could have two plants directly under each light and they, both lights and plants, would be placed close enough to your reflective material so if you use quality reflective material they would get a lot more light to the outer and lower portions of your plants and that means more buds of decent to good size instead of a bunch of popcorn and your plants are not so tightly packed as to block that needed light to the lower portions between your plants.
You would have more light area coverage than you would need for your sq. ftg. but that would allow you to overlap some light from each light, so again the plants when grown like that receive a lot more light to areas that can be very difficult to get adequate light to when using 250-watt lights.
　
That might not sound all that good to you but it is what worked best for me when I grew using 250-watt lights. At first I thought I would yield more with more plants but later I found that I could grow fewer plants that produced much better and I came out ahead in several ways, right down to the numbers of beans I had to buy and how many plants I had to care for and fewer pots and less soil and less fertilizer/nutrients/supplements used and I had more and better bud.
　
You might wish to consider it but if it is totally different than what you planned or hoped for then just ignore it and do what you will feel most comfortable doing. Like possibly picking a different wattage lighting system or something.
