D&D 5E Effective Illusions

[jaelis]

As illusion an certainly stop you from seeing something, otherwise it wouldn't work at all. So if a medusa was holding still, an illusion of a towel over her head would block her gaze. But it would be harder if she were moving.

But compare to an illusion of a box over a lantern. You wouldn't be able to see the lantern, but would it still illuminate the room? I would say yes.

 

[Whizbang Dustyboots]

That makes a fair amount of sense. Many thanks for the clarification. What about light selectivity in an illusion? Can an illusion be used as a customized light source? I was thinking about light sources that can only be seen by people with infravision or ultravision. Or adjustable light sources for non combat environments. What would your take be?

Illusion spells are already powerful enough. Creating effectively invisible light sources is such a good effect that it seems like way too good of a giveaway to add to illusion spells.

And, as has pointed out, illusion spells create fictitious images, not real ones -- even illusory fire creates illusory light and shadows, based on the caster's understanding of how those work. At best, if illusions do have infravision and ultravision components (and that's not necessarily true, given that everything beyond the basic visual has historically been added in upgraded versions of the basic spell), it would be based off the caster's knowledge of what would be shown in those spectra, which would likely require them to be able to see in that spectra and know how light and shadows look in them.

That said, light sources that only certain people can see is a kickass spell with lots of applications, and well worth a party spellcaster researching.

 

[Whizbang Dustyboots]

Final clarification then. Can an illusion block light? Using the Phantasmal Force example from before actually interrupt the Medusa gaze? Or does the illusion make you think you are looking at a box, giving your statue an unusually calm expression? If it can block light and can stop the gaze attack, would a minor illusion of a towel be enough?

Yes and no. You can create the illusion that the light is blocked, but the light is actually getting through, and you're just creating an image of an unlit area instead. Outside of the range of the illusion itself, the light would still be cast and visible.

Illusion spells do not negate the need for darkness spells.

 

[jgsugden]

PCs are heroes in a tale of fantasy. Illusions are opportunities to let players weave creative heroic stories. If it doesn't contradict the rules, let it work.