Watch the Playing Over The IV Chord online guitar lesson by Brad Carlton from Guitar Lab: Thirds and Sixths

The Lydian mode is the fourth mode of the major scale and it's formula is: 1, 2, 3, #4, 5, 6, 7. When these notes are aligned in thirds (the heptatonic arpeggio), the numbers are as follows: 1, 3, 5, 7, 9, #11, b13. Knowing this information will help you organize your thirds based upon the prevailing harmony.