Image courtesy of SOHO/EIT consortium. SOHO is a project of international cooperation between ESA and NASA.


General information about measured samples is listed in Table 1. Besides brand name, model, manufacturer or retailer, and nominal power, any additional information that may affect the results is given.

In Table 2, irradiances as microwatts per square centimetre and percentage proportions of UVA, UVB and UVC from total irradiance are listed. Using equivalent values given by manufacturers, general comparisons to other models outside this test can be done. However, it has to be certified that the UV ranges have been specified with identical ranges: UVA 320-399 nm, UVB 280-319 nm, and UVC 250-279 nm.

Table 3 shows irradiances in the UVB range. Separate values have been calculated for the wavelength range that mainly contributes to vitamin D3 photosynthesis (UVB-1, 280-304 nm) and for range above it (UVB-2, 305-319 nm) that may potentially destroy vitamin D3. Bernard (1995) calls range 290-300 nm as ”D-UV”, but in order to maintain consistency with the naming conventions (UVA, UVB, UVC), the sub-ranges of UVB are designated here UVB-1 and UVB-2. The ability of a lamp to efficiently produce vitamin D3 can be evaluated by comparing values in Table 3. The higher the irradiance of UVB-2 is in comparison to UVB-1, the higher the probability that UVB-2 radiation will start destroying cutaneous vitamin D3.

Table 4 lists the D3 Yield Index of the target and the percentage of UVB from total output for comparison. While calculating D3 Yield Indices, the lack of accurate data made it impossible to take into account the above-mentioned possibility that weak radiation in the UVB-1 range, combined with strong radiation in the UVB-2 range, may cause photodestruction of vitamin D3. Thus, if a lamp has a high UVB percentage but a weak D3 Yield Index, it might suggest destruction of vitamin D3. In this case it will be necessary to closely examine the spectral curve of the lamp at UVB/UVA crossover point in order to evaluate the situation.