You would need to use UV bulbs inside the tank, as glass, etc. filters out nearly if not 100%, as Homer says. That would be difficult to do in a small terrarium without overheating, dehydrating or giving your frogs a fatal sunburn. While darts in the wild in rainforests do get some UV, it is mostly filtered and reflected from the surrounding vegetation. They are not baskers as some lizards and turtles are. Most of us supplement with Calcium and D3 instead. In a huge rainforest/zoo set up, it would be possible--but few of us have that option and the supplement dusting of vitamin/calcium plus D3 works.
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Patty
Pahsimeroi, Idaho
4 D. auratus blue
5 D. galactonotus pumpkin orange splash back
5 D. imitator
6 D. leucomelas
4 D. pumilio Bastimentos
4 D. fantasticus
4 P. terribilis
4 D. reticulatus
4 D. castaneoticus