The Exon Terra Reptile UVB200 emits the ideal UVB spectrum for optimal Vitamin D3 photosynthesis. The Reptile UVB200 Bulb is especially designed to simulate conditions for reptiles with very high UV requirements, like diurnal reptiles from desert environments.nthese areas receive direct unfiltered sunlight with high levels of UVB. The significantly high Vitamin D3 yield index results in increased vitamin D3 photosynthesis to aid calcium absorption and prevent metabolic diseases.nthe extended UVB penetration makes this bulb the ideal choice for taller terrariums or terrariums with denser screens.