Can magical darkness affect a magical light source that is in a sealed container?

Question

From the Darkness spell in PHB:

Completely covering the source of the darkness with an opaque object, such as a bowl or a helm, blocks the darkness. If any of this spell’s area overlaps with an area of light created by a spell of 2nd level or lower, the spell that created the light is dispelled.

Suppose somebody casts Light or Continual Flame on a coin or similar small object, then drops it into a sealed opaque container.

Would they be able to carry it through the area of a darkness spell so long as the container remains sealed?

Stands to reason that if the Darkness can be blocked if it's completely covered, then it would also not be able to penetrate the container, even though the container is within its area of effect - i.e. is the Darkness's AoE limited to "outside the container" and the Light's AoE to "inside the container", so that they don't actually overlap?

Answer 1

The light is not dispelled

The PHB explains how to determine if something is considered part of an AOE or not:

If no unblocked straight line extends from the point of origin to a location within the area of effect, that location isn’t included in the spell’s area. To block one of these imaginary lines, an obstruction must provide total cover.

And the container counts as being full cover:

A target has total cover if it is completely concealed by an obstacle.

The light source, being completely sealed in an opaque container, effectively has full cover against darkness. No "unblocked straight line" can possibly get from the outside of a sealed container to the inside. It is physically obstructed from all sides.

This means that darkness does not have a clear path to the light source or any of the light that it generates. And, by extension, there is no way for the areas to overlap. Thus, darkness cannot dispel it.¹

In the end the light is not dispelled but no light is visible in the area of darkness either.

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^{1 - This might be true even for a transparent container since glass still provides total cover, though this is sa bit of a weird case. The light source still has complete cover against darkness which means that darkness has no clear path to get in. Thus, even in a transparent container darkness is not able to dispel light.}

^{However, by this same logic light has no clear path to get out which strangely suggests that putting light in a transparent jar prevents it from shedding light outside of the jar. See this question for discussion: Will the effects of light shine through glass?}

Answer 2

The light is not dispelled provided no light escapes the container

As OP quoted:

If any of this spell’s area overlaps with an area of light created by a spell of 2nd level or lower, the spell that created the light is dispelled.

If the light spell is allowed to affect an area outside the jar, the darkness would then overlap at least a portion of the area of light and thus dispel the light effect.

In other words, the description states only an area of the light needs to be overlapped, not completely encompassed, for the light spell to be dispelled. This means that even if the source of the light is protected by the encasement, the darkness "touches" any light emitted which is dispelled at the source. Anything which prevents the light or darkness from penetrating it would safeguard the light's source.