I think in most (or maybe only some) Northern regional accents, "look" and "luck" use the same vowel sound (unless people do pronounce "look" like Luke, my mum does sometimes) whereas sown South they use different vowel sounds. I say "luck" and "look" exactly the same.
Same with "put" (as in to put something down) and "putt" (golfing term, dunno what it means
). I'd use the same vowel sound for those two but my Southern friends use different vowel sounds.