((I'm also assuming that the less frequent they are, the more merciful you will be with energy cost, Nakeen.))
((Exactly. All Artifacts can generate some energy to power themselves, and depending on the frequency, it may or may not use too much energy than it can produce naturally.
When used by a god, the Artifact will never run out of power as long as the god has Energy left.
But when independent or used by some lesser being, the Artifact will use its own power. For these, it could be smart to give an auxiliary power source.
Simple example : An Artifact sword that can emit flames. Simple. When a mortal takes the sword, it will burn, and if the mortal overuses the powers of the Sword, the flames will eventually run out.
One could then add the following to the Sword : it consumes blood/flames/courage/something to refill its energy reserves.
The only rule to the Resource must be that it is either an "Element" as in something that can be interacted with physically. Any "Mental" Resource will be seen as a subdivision of the "Mind" resource.
[And Yes. I just made it up
]
Oh and of course, I won't keep track of Artifact power left. I will just do it on an interpretation basis.
Sorry if it seems like I'm over complicating things when you all just want to create a Day/Night cycle. But I'm being strict for this because if I don't properly set rules/limitations over an effect affecting a huge area, I fear game-breaking alterations may appear.
GM thought: If Day/Night could be created for the whole World cheaply, then it would mean one could easily create an effect killing off all mortals of the world easily. Or even screw everything up easily.))