So if I understand what you want is to light the center section of each bar in the center and have a darker outside, is this correct? If so then you are going to have a lot of math to do to make each light beam appear at the proper location and change the grid map to account for the offset needed for the bars further from center. OR curve the backdrop to keep the light the same distance away. Another way would be to create a material zone on each bar down the center so that you can make it a light emitter that way the light will always be coming from where you want it to appear. Since the light does not line up on the girl to keep it in line with the grid adding the extra mat zone would probably be the most accurate way to get the look you are after.

Poser 5, 6, 7, 8, Poser Pro 9 (2012), 10 (2014), 11, 12, 13