Too much can hurt
Too much UVB can hurt the cham. 10's are for desert dwellers that are used to more direct harsher sunlight. 1 5.0 should be sufficient so long as your cham has unobstructed basking several inches under it. Use the other for full spectrum or heat if possible.
Also, if possible, give your cham as much direct sunlight (unfiltered) as you can when the weather allows. This is beneficial both physically and psychologically.