Turning lights off to warn swimmers end of session; unsafe?!

In our county's largest swim facility some of the lifeguards on the last shift have decided to turn off the inside lights to warn swimmers it is nearly time to close the pool. In this indoor facility there are no in pool lights so turning off the lights leaves it pitch dark for a second or two. Some of us who occasionally swim late have complained to the lead lifeguard but they shrug and do not see this as an issue. One of the lap swimmers slammed her head into the side of the pool this past week when a guard held the lights off for well over 2 seconds. But we were told "go ahead and complain to management..." by the guards. No response. I can't believe this is OK from a safety standpoint but cannot find a relevant Red Cross or standard pool management practice to show the lifeguard team this is unsafe. Do we have to get the woman who hit her head to go to an urgent care facility for the bump on her head and then have them file an insurance claim to get the facilities attention? I was a lifeguard decades ago and this seems to clearly be an unsafe practice by a few guards unwilling to use the running timer or some other means to alert swimmers that won't impact swimmer safety. Thanks for any suggestions!