Will 400w HPS support 2 autoflowering plants?

I am looking into buying lights. I cant use up many amps so was looking to keep it below 400w. Is a 400w HPS light enough for two lowryders? Should I go 600w, or maybe I can get away with like a 250w HPS. I am growing in a grow tent with a floor of 2 x 4.

rule of thumb (depending on bulbs lumen outpust)

250w 2.5x2.5
400w 3.5 x 3.5
600w 4x4
1000w 4.75x4.75

600w lights give the most lumens per watt

(lumens/watts= lumens per watt)

My buddy had 10 small, topped plants (2.5 feet) under a 400w

I'd go with the 400 but make sure you can cool it.

ya man that 400w will do the job very well. you could even probably get away with the 250w. just remember the 400 will give you much better results so if you can afford it, use that

Thanks guys, I will prolly' be getting a 400w'er