I would not recommend that bulb for your box turtle. That type puts out very little UVB. It must be mounted horizontally and be in a reflective aquarium style hood to put out any usable UVB at all. Even then you will probably need to have it 4-6" away to get a decent UVI reading.
I would recommend going with a straight, linear flluorescent tube for your turtle. Get an 18" fixture and a 10.0 UVB bulb. Should be able to mount that about 12-14" above the turtle level.