What does "When living light should kiss it?" mean in Macbeth?Act 2 scene 4

The meaning of this line is that it is supposed to be light. It
is daytime and therefore it is supposed to be light.

In this scene,
all kinds of crazy and unnatural things are happening. Ross and the old man think that these
things are happening because Duncan has been murdered. The idea is that nature itself is upset
because of the killing of the king because that upsets the natural order of
things.

If you look at the lines before the line you cite, you can
see that this makes sense. The lines are:

readability="10.029411764706">

By the clock ’tis day,
And yet
dark night strangles the travelling href="../../macbeth-text/act-ii-scene-iv#prestwick-gloss-2-4-119">lamp.

Is't night's href="../../macbeth-text/act-ii-scene-iv#prestwick-gloss-2-4-120">predominance, or
the day's shame,
That darkness does the face of earth entomb,(10)
When
living light should kiss it?

Ross is
pointing out that it is supposed to be daytime but the face of the earth is in darkness when
living light is supposed to kiss it (when it is supposed to be
light).