The illusion has two "states": one for those who see the illusion, and a transparent version for those who have disbelieved it. Both situations are existing at the same time for different creatures. So my understanding is there is something about looking at the illusion (which is not really there) that alters the viewers mind. The viewer either interacts with it and reveals it is an illusion or investigates it and figures out it is an illusion. At this point, the illusion loses its hold on the viewers mind, but the illusion itself (the magic supporting it for a minute) does not change.

So at that point, I would think that any scientific explanations about light and what not go out the window. The magic of the illusion does not block light, it alters the viewer's perception of whether the light (and visible objects on the other side of the illusion) are blocked.

Honestly, I think this explanation makes the spell more interesting to me. The party enters a room lit by a single torch, and the party (somehow) has no active sources of light and no darkvision (yeah, work with me here). As the party enters the room something casts minor illusion on the torch to block it out. At the point the party sees the illusion around the torch, the magic takes effect in their mind and the light in the room goes out. The party is now in (as far as their minds will accept) darkness. Meanwhile, if someone in the room had cast minor illusion on the torch, they know that it is an illusion, and the room does not go dark for them. The party can either activate other light sources or investigate or interact with the illusion around the torch, at which point the lights come back on for anyone successful with that.

So my ruling would be "If the illusion was a real object, how would it affect the environment in terms of vision and light?" and go with that alteration of the viewer's mind until the viewer works out what is going on, but it does not actually​ block the light.