If you talk to any DP or SPARK they will all say that you need to light each and every scene, whether it be a bright summers day in an open field or not. But depending on your movie, and the length of the scene, you may get away with it as outdoor lighting set ups are generally quite expensive. It just depends on the amount of money you have for this particular set up.

MOVIE MAKING FAQ - http://www.moviemakingfaq.com

Ok - I have a question. Let's say you're shooting a mid-range shot, where you see the actor's full body on the screen, outside in bright sun. Your camera is about 10 feet or so from the actor and so your reflectors must also be at a similar distance to keep them out of the frame. Will the reflectors still make a difference from that distance? We shot some scenes last weekend and it didn't seem to do a whole lot using foam core.