If you see an intruder, lighting him up with a high lumen flashlight and issuing a verbal command seems to be a fairly good idea.
Verbal warnings have worked for me three times in the past, in that no shot was required; I did not have, nor did I need, a flashlight.
In none of these instances was the intruder armed with a firearm, and in each case, he was alone.
It would seem to me that giving away one's position by using a fash light on the gun and calling out might prove very disadvantageous in the event of an invasion involving more than one participant, particularly if one or both had firearms, unless one is behind cover in a "safe room." Under those conditions, with little chance of an ambush or crossfire, the idea of illuminating the target and issuing a warning sounds reasonable.
Does anyone happen to know what is advised regarding warnings in the NRA Personal Protection in the Home course?