Ordering the Modes from Bright to Dark

Brightness in a mode comes from how many notes sit a half step higher versus lower relative to the major scale pattern. Lydian is the brightest mode because its raised fourth degree avoids any pull toward darkness every other note sits where you expect. Locrian is the darkest because almost everything is lowered, including the fifth degree, which destabilizes the whole scale. Between those two extremes, the modes form a line: Lydian, Ionian, Mixolydian, Dorian, Aeolian, Phrygian, Locrian.

The mechanism is simple: moving one step down this list lowers exactly one more scale degree by a half step, compared to Lydian. Ionian lowers scale degree 4 (Lydian's raised 4th becomes natural). Mixolydian lowers that same 4th plus degree 7, giving it a flatted seventh instead of a leading tone. Aeolian goes further still, and Phrygian lowers degree 2 on top of everything Aeolian lowers, which is why Phrygian has that flat second pressing down into the tonic. Each mode is the previous one with one more note pulled down.

This ordering matters because it connects directly to how modal harmony behaves differently from major and minor key harmony. A mode's brightness or darkness predicts the character of chords built on its scale degrees: Lydian and Mixolydian give you major-feeling tonics with an unusual color note, while Phrygian and Locrian give you unstable or minor-feeling tonics. Locrian breaks the pattern entirely, since lowering the fifth degree makes its tonic triad diminished rather than major or minor, so it cannot function as a true home base the way the other six modes can.