Night flight (6)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">night flight</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for redeye that I've seen before include "cheap whiskey" , "Undesirable effect in photo produced by flash" , "Flash-induced effect on photo" , "early flight" , "Effect of reflected flash on portrait" .)