UV-lamps for terrariums: Their spectral characteristics and efficiency in promoting vitamin D3 synthesis by UVB irradiation

Abstract

Sufficient irradiation within a narrow sub-band of the UVB range is a prerequisite for the photosynthesis of vitamin D3 in skin. Although radiation below wavelength of 300 nm (nanometres) promotes photosynthesis of vitamin D3, radiation above 300 nm destroys vitamin D3 that has been already synthesised in skin tissue or obtained nutritionally. Furthermore, skin temperature has a significant effect on the pace of vitamin D3 synthesis. In terrarium, the required UVB-radiation has to be artificially produced with dedicated lamps. In the study, the characteristics of light produced by fourteen different models of UV and full spectrum lamps specifically designed for terrarium use were measured over a range of 250-800 nm. As a reference, the spectrum of natural sunlight was also measured when the sun was at its highest point of elevation in the southern sky of Finland. The proportion of radiation energy that takes part in the photosynthesis of vitamin D3 was determined and the D3 Yield Index was calculated. Significant differences as large as thousand fold were found in the D3 Yield Indices. It is concluded that the percentage of UVB radiation from the total radiation figure does not necessarily give a true indication of a lamp?s capability to maintain cutaneous production of vitamin D3.