Can mundane light penetrate magical darkness to illuminate regions outside the dark space? And can its source remain lit when inside the darkness?

Question

Consider magical darkness like that created by the Darkness spell or by the Darkmantle creature's Darkness Aura. Both say that mundane (natural) light can't illuminate its darkness and that their darkness will dispel any spell of 2nd level or lower whose illumination overlaps it.

Now consider carrying a light source toward a 5-foot-wide wall of magical darkness. If it's a 2nd-level (or lower) source of magical light, the source will be dispelled the moment its lit area touches the wall. However, if it's a mundane light source like a lit torch, some interesting effects may arise:

1. If the torch is close to the wall of magical darkness, will its light still somehow penetrate that darkness to illuminate the space on the wall's opposite side?

2. If the torch is brought into the wall, will it remain lit?

3. If yes, will that torch inside the wall still illuminate its usual regions outside the wall, similar to #1?

Or, restated: can mundane light penetrate magical darkness to illuminate regions outside the magically darkened space? And can a mundane light source remain lit when inside magical darkness?

Answer 1

Darkness creates a heavily obscured area that is blocking light, but does not extinguish torches

The mechanical implementation of darkness — magical or mundane — in 5e has little to do with how darkness works in the real world, because it creates a heavily obscured area (p 183 PHB):

A heavily obscured area—such as darkness, opaque fog, or dense foliage—blocks vision entirely.

The game makes no difference between fog and darkness: they block vision and light in the same way. Hence, no light will shine through your magical darkness and be visible on the other side or illuminate it.

See Does the Darkness spell block vision? for a more in depth discussion on how to deal with this unexpected result.

To answer your sub-questions:

1. No — see above
2. Yes — darkness does not say it affects mundane light sources in any way, only that their light can not illuminate it. As spells only do what they say they do, it will not extinguish the torch.
3. No — same as 1.