Hi, I installed the lamp about 3 months ago. According to the instructions, the distance between the holes is 285mm. Philips assumes that the hole is just in the middle between them, the plate has a recess just there.

The dimensions of the mounting plate are approx. 23cm x 58cm. I can't see the exact position of the holes in the assembled state, but they were quite far in the corners. The material is easy to drill with a steel drill bit. I have routed the power cables in a different position.