You're missing a comma/semi-colon/hyphen after the first verse. I think if you change "peeked from" to "peeked through" the imagery would be a bit clearer, but it's fine the way it is.

I really, really, love this. The title itself is ominous, painting a stark image before you delve into the poem itself. The light not flickering and the room feeling empty makes the reader think the speaker has come to expect the light to flicker (flickering lights makes one think of spirits) and the speaker personified someone important to them to be 'light', making an appearance through thunder/candle and then goes on to reiterate they feel amiss without their presence. This poem is general in the sense it could mean a lot of things, but to me it means absence.

One of my favorites from your most recent. That's why I had to nominate this one, because it spoke to me the most :)

The title provides more depth to me - not just a power outage on the surface, but a darkness that can be felt even in the light. An emptiness even in their presence, perhaps?

Those last two lines, on their own, bring this poem even more reflection, that self-admittance... and the image of the candle dancing, maybe visualizing the memories, having them come alive in the milliseconds of darkness, it's too much to bear. To process.

There is mystery to this, and tangible sorrow.