I TAKE Candle!

Very easy if you drop the candle in a central location every time you go to a new room. Clear out the room in the candle light, run out into the dark to complete objectives or loot, then make your way to a fresh candle. Rinse and repeat. Also worth noting that if you're having trouble surviving with Brann as DPS, tag it and let Brann do all the work. If you're Guardian I suggest not entering bear form whatsoever.

Blizzard announced that this achievement would no longer be obtainable as of the start of Season 2. However, it seems it's gone as of the launch of patch 11.1. As I post this comment, we're in that weird week after 11.1 launched but before S2 starts. The function of the candles and totems has changed: instead of the S1 mechanism of "it works while carried and depletes with every step you take" you now just pick them up and have to place them on the ground for them to work, and they don't do anything while you are holding them. They also don't have a depletion mechanic any longer. So this achievement seems no longer obtainable.

If you die with the candle and pick up a new one, you STILL will get the achievement - confirmed on Level 8 Delve solo.