After another creeper blew up in my homecave, I felt like I really miss NEIs F7.
Till NEI not yet available for 1.11.2 and I failed in searching alternatives, I made a simple mod for highlighting areas with light level lower than 7.
No UI for toggling it, and algorithm is only checking for light level lower than 7 (no slimes, no mob size checking), area update occurs only when player moves... but it still does its job.
Here's code: https://gist.github.com/cab404/4143e51ae4add080bebfc2a806aa601b
Here's JAR: https://cab404.ru/all/bin/trash/moblightlevels-1.0.jar