A standard pair of lightframes started out its life as a pair of sunglasses. Wires run between the mirrored shades and the opaque inserts, from the bulbs to the corner of the sunglasses, and from there down to a mini headphone jack. For most of a decade now, not only has this design been standardized across all manufacturers, but pretty much so has the layout of the lights. Normally, there are four of them, arranged in diamond pattern about an inch across, over each eyelid. Your eyelid further scatters the light, hopefully producing a nice, evenly lit field of light on the back of your retina with each pulse.
Polarity is definitely the more important of the two.
All of the lightframes on all of the machines currently on the market run the wires from the lightframes to a standard headphone jack. The parts for it are easy to come by, sturdy enough, compact, and dirt cheap. The only problem this creates is that it is possible to plug the lightframes into the headphone jack and vice versa. But despite that problem, that's the way everybody does it now. What the industry did not standardize on is the which wire goes to which part of the jack.