How do you envision setting this up, in terms of arranging the buckets? Long rows are not conducive to the light footprint of small HID lights. You might be better off with high output tubes, logistically speaking. Light distribution will be more even and controlled than with a small HID, where the difference of light intensity on the leaf surface may vary significantly enough even in a small setup to influence growth along with whatever factors you want to isolate and so degrade the reliability or accuracy of the measurements you want to make.