I know a few things about German signal boxes, and I doubt the Polish ones will be too different in this regard.

Railway signals have a “daytime” and a lower “nighttime” intensity to make sure that the driver sees the red signal in the summer sun, but doesn’t get blinded by the same red signal on their final run of the day at midnight. The switching between these intensities is done on the signaling panel and I assume that’s what the big switch is for.