Tropical plants may require a higher UV level in the light, if not to grow, maybe to fruit. Are there studies / sources on that with actual quantities?
Bamboo suggested in her answer to look at this page on UV strength, which I had seen already. It is slightly helpful in that it shows that, for instance, Germany in the summer can expect roughly half the maximum UV input as, say, Cuba, gets all year round.
However, the tropics don't have seasons, so a comparison would have to take into account seasonal differences in temperate latitudes. Also, while it does linearly relate to UV intensity, the UV index is adjusted for how damaging the UV is to human skin, so different wavelengths are weighted differently. This might be inadequate for thinking about plants.
Finally, while knowing the typical UV levels for a plant's natural habitat is a start, it would be better to know what irradiance it actually requires, how much, what wavelengths, what rhythm.