Mode
Bb Lydian
The Bb Lydian mode (also written A#) — Bb C D E F G A — shown across the guitar neck.
Also written A# Lydian. A# and Bb are the same pitch, though spelling it from A# would need double accidentals (A# B# C## D## E# F## G##), which is why Bb is the name in use.
Swipe the neck sideways to see the higher frets.
Bb Lydian is the major scale with one note changed — the #4, E. That single note is what the mode sounds like; lean on it and the colour is obvious, avoid it and you are just playing major.
Notes
Bb C D E F G A
Intervals
1 2 3 #4 5 6 7
Parent scale
F Major
Degree of parent
4
The tool shows this from its parent key, F major, with Bb marked as where Lydian begins, the same seven notes centered on F.