Generally, our larger C9 bulbs are more common outdoors where they might be viewed from a greater distance.
C7 are great indoors on your tree or wreaths or any other decor. That being said, C7s can be used outdoors and C9 can be used on trees if you want – there are no strict rules and you can use any size of Tru-Tone bulbs anywhere you like! We like to mix and match ourselves!