User blog comment:Zathronas/Analysis by an author: Volume 2 episode 11: No brakes/@comment-3146930-20141024021616/@comment-9090085-20141024031208

I always thought of it like this: Yang's semblance switches between a "passive" state and an "active" state. She always passively absorbs energy and stores that energy in her hair. When her semblance "activates" her eyes turn red and she releases the energy she has stored up, causing her hair to glow.

Thing is, her semblance "activating" and her having energy to release has no correlation to each other - Take the fight with the Ursai, for instance: Her eyes turned red, but her hair didn't glow; and her punches weren't any stronger then before she got mad(she was throwing 'em around to begin with).

Just my 2 cents.