Illumination technology

We still have our combined Christmas light display up outside; J. wants to keep it until spring. Several of the strands have partially failed, that is, around the halfway point they've gone dimmer or entirely out. The interesting part is that some nights, they revive, a bit. Of the two purple strands, the further one is now almost entirely functional again; the pink strand has some light if you look really closely, and tonight even the blue strand had some life in it. Is it a matter of humidity? Temperature? Hard to say.