White Pass & Yukon Alco DL535e gyralite usage

Has anybody ever seen the WP&Y use the red gyralite that is on top of the cab roof on thier big Alcos? Of all the videos I have seen, even running light in reverse, I have never seen that light turned on. Is it only for emergency brake applications? That would seem like a waste of an expensive warning light. Hoping someone has a WP&Y employee timetable that has what that lights use is. Mike