Major vs. Lydian

The first of these is the major scale - Ionian, in Greek-mode terms - and both start on C.

C Ionian holds a natural fourth against the tonic - the darker of the two.Hear C Ionian in the app

C Lydian raises that fourth by a semitone, into a sharp four.Hear C Lydian in the app

The wheel makes the difference positional rather than verbal: the fourth-degree wedge sits one wedge further clockwise in Lydian, and the spoke drawn from the center recolors to the interval that degree now forms with the tonic. Everything else on the two wheels is identical.

That single degree is why Lydian is called the brighter major - raising the fourth removes the only note in the major scale that leans toward the tonic from above, leaving a scale that floats rather than resolves. Reading it is one thing; the difference is much more obvious held under a drone, which is what the links under each figure are for.