Just try to have some diffused dappled exposure, as in a latticework, for turtles to bask from under. They will expose themselves with spot illumination as they choose. They prefer to remain hidden, so it has a definite psychological benefit to allow them a mechanism to bask from under cover/while hidden. They like to remain with a couple of steps from cover.
Make sure they have plenty of moisture/humidity/water. Many people raise their baby box turtles in a semiaquatic environment.
Good luck.
jsc
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"As hard as I've tried, just can't NOT do this"
John Crickmer