Normally when you take Eclipse, you gain energy of Etheric. However, as you progress through the game, you can find different ways to view the world, and different ways to view the ether. There are currently three Sight effects:
These effects replace the generic Etheric effect, but function identically (with a few effect-specific bonuses as well).
Fae Sight and Ocean Sight are mutually exclusive rewards for the Dock Song quest, from the Fae Eyes and Ocean Eyes skills respectively. Muffled Sight is a reward from the Punk Uprising quest, from the hefty capsule.
For the Fae/Ocean skills, whenever you would gain energy of Etheric, you gain energy of Fae/Ocean Sight instead. If you have any energy of Etheric when you gain the skills, it converted to Fae/Ocean Sight.
Hefty capsule work slightly differently - taking one converts your current turns of Etheric (or other Sight) to Muffled Sight, and gives you 15 more. If you would gain any more turns of Etheric afterwards, you gain Muffled Sight, as long as you still have it active.
See also: Eclipse Duration