Not all interviews are conducted inside an office.  If you are one of those few people who get to interview outside and its particularly sunny outside, be sure to take your sunglasses off before starting the interview.  How will an interviewer gauge your eye contact if they are hidden behind sunglasses.  If its too sunny, you can always ask your interview if you can move to a shadier place so you don't need to use your sunglasses.

Eye contact is critical in an interview.  You don't want to have the eyes hidden by sunglasses or constantly look squinty as the sun shines in your face.