Searchlights sometimes being used - sometimes not

[FAdmiral]

Here is something I experienced in dealing with a DD looking for me.
As soon as my torp hit the cruiser, the DD to my port side turned
on the searchlight and started to scan the area. I (at PD) downed the
scope and continued moving a 2 kts. The DD came to a complete stop
just behind me scanning the water on the opposite side (using external
cam for testing). I made a 90 degree turn to starboard to pursue the
damaged cruiser, still creeping at 2 kts but no silent running. The DD
was still stopped using the light on the other side. As soon as I got
slightly ahead of the DD, I heard pings. Almost immediately the DD turned
off the light and picked up speed and turned in my direction to start a DC
run. I went deep immediately and did a full right turn at flank speed.
He dropped close but too shallow to give me any damage. As long as I heard
the pings, the DD did not use the light. After awhile the DD lost me and on
came the light again. Conclusion: If they hear you underwater, why use the
searchlight....

JIM