Thinking of Modes as the Major Scale starting on a different degree leads to confusion and frustration.
Many people think that if they have a Cmaj chord playing on the back; and they start the C major Scale from the 4th degree
(F -G - A - B - C - D - E) somehow they think that they are playing a C Lydian.
They are not. They are still playing a C major Scale.

The set of notes you see above correspond to F Lydian not C Lydian.
But, in order to get the characteristic Lydian flavor you should play that set of notes over an F major chord.
Fmaj chord. (F, A, C)
F Lydian Mode. (F -G - A - B - C - D - E)

Now, if what you want to do is play a C Lydian you’d play a Cmaj chord and over it you play this set of notes:
(C - D - E - F# - G - A - B)

If you got confused by what I just said, do this:
Record yourself playing a Cmaj chord for a few bars.
Play it back in a loop.
Pick up your guitar and try the following Modes:

C Ionian. (C, D, E, F, G, A, B)
C Lydian. (C, D, E, F#, G, A, B)
C Mixolydian. (C, D, E, F, G, A, Bb) This is a Dominant Mode, more on that later. For now go ahead and play it.

You should hear the difference and the “flavor” of each mode.
Once you get those sounds in your head, you will be able to call them at will when you are playing.
Make sense? :)