If you rule that a seeming of a Flashlight cannot create real light, can it create illusory light?
At one point in the books, Harry has the demon in his head use her illusion powers to let him see where everything is/was while in a dark room
. For immobile objects, and for objects that you can detect in other methods beyond the visual while not currently being able to see them, it works perfectly. Outside of the nitty-gritty of actual physics, does it make a difference?
What exactly is the player trying to get out of a seeming of a Flashlight? An illusion of light wouldn't trigger a photovoltaic cell, for example, which could be both good and bad; and wouldn't be visible to anyone who wasn't subject to the illusion.
There are advantages to a group of people, instead of using an actual light source, having one member who can use some form of non-visual perception (spell-based or otherwise) to "see" their surroundings and then project an illusion onto the group giving them the equivalent of sight.