The Minor Illusion spell say:
If you create an image of an object – such as a chair, muddy
footprints, or a small chest – it must be no larger than a 5-foot
cube. The image can't create sound, light, smell, or any other sensory
effect. Physical interaction with the object reveals it to be an
illusion, because things can pass through it.
Can the illusory object block light? And if not, what would a creature see?
For example, could a vampire mage use the Minor Illusion cantrip to protect himself from the light of a sun blade? Could a wizard create an illusory box around a torch to "turn off the lights"?
Best Answer
No, it can't.
When the book references this, it's not just talking about a physical object like a rock. "Things" accounts for all things. This illusory object impedes nothing and is only an illusory trick of the eye, but this is where the concept of magic comes in. Things can pass through the illusory objects even if a creature or player can't register it passing through with their eyeballs. The effects of those things impacting a player would still apply (and perhaps give them a hint as to the object's illusory quality).
There are some great opportunities here for roleplay. I feel like it'd be really interesting to be able to feel the warmth of a torch or fire behind by an illusory wall. I feel like a wizard casting Minor Illusion to block the light of a campfire from an enemy patrol is an engaging and creative use of the spell.
I would ultimately say that it's up to you to decide where to draw the line, but that the rules state this is nothing but an illusion and doesn't have an effect on any properties of the world around it.