(The title gave me a bit of trouble, so if you have a better idea on how to title this question after reading it, feel free to suggest it or directly edit it.)
Light levels (bright light, dim light and darkness) can have many effects on combat, and are sometimes necessary conditions for certain spells or abilities. While common ways of manipulating them are simply using light-emiting items or spells, an out-of-the-box approach a player proposed to me today made me rethink how this system works, and especially how to create darkness.
This approach was quite simple : instead of getting rid of a room's light source, the player wanted to isolate themselves from the room's light altogether. Using a large piece of opaque fabric and some extra objects prepared in advance (for instance, their polearm), they could quickly put this fabric in a tent-like shape, barely large enough to isolate them from the room's light.
Behold my incredible drawing talents as I show a rough sketch of the player's idea (you could also add light weights to the ends of the piece of fabric to make it easier for the fabric to stay in place) :
To put it simply, the plan is to raise the center part of the fabric around the character to make it form this "area" around the character. Because the fabric is opaque, no light can go through, so if the inside can be considered an "area", it would be in darkness, or at the very least dim light if you consider the opaqueness of the fabric to be low.
While, at first glance, this seems quite ridiculous, I could find nothing in the rules that prevents this from working. Nothing about a minimum size for an area with a different light level, or anything like that.
This kind of situation could allow them to trigger darkness-related effects, such as Twilight Cleric's Steps of the Night feature (this was the specific example my smart player used). To some extent, using a lantern or another similar light source could allow to use brightly-lit-related effects without giving away your position in a dark area (I couldn't find one on top of my head, but the result would most likely remain the same as the previous situation).
At this point though, it becomes difficult to draw the line. What about throwing a blanket on someone and saying "they're not in the light anymore"? Or what about using a large piece of cloth to obscure the corner of a room? As far as I've seen, nothing in the rules really helps.
Is there anything that I missed in the rules that either validates this as a legitimate strategy, or otherwise deny it? Or is this another case uncovered by the rules, and effectively dependant on the DM's decision?
