lucid

Clear; easily understood.

[T]he book, constructed in short, lucid episodes, can be satisfyingly read as a sequence of provocative talks, at once well informed and vatic.

Mentally rational; sane.

Bright, luminous, translucent, or transparent.

The atmosphere was unusually clear, as if loath to part with the daylight; but the moon, like a round of lucid snow, had risen on the sky; and a pale, soft gleam, came from the lamps amid the foliage.

Pictures of growing spring and farms and homes, / With the Fourth-month eve at sundown, and the gray smoke lucid and bright, […]

A lucid dream.

The day before nightmare-initiated lucids, subjects reported more depressed feelings[…]

A surname from Irish.