Distribution of UV light
When comparing the distribution of ultraviolet light in the UVA, UVB and UVC regions, the strong emphasis of UVA can be seen in all results (see Table 2). Many of the lamps have over 30 % of their total radiation in the UVA range. Although this may be detrimental to vitamin D3 synthesis, according to some reports it might have a positive effect on reptile behaviour (Gehrmann, 1994). There is not much research material available on this subject. Human studies have given contradictory results. In humans it has been found out that UVA can cause eye damage (for example yellowing of the lens of eye), premature aging of the skin, and changes to the immune response. Because of this, excessive amounts cannot be recommended for animals either. In any case, the UVA irradiance of all lamps measured is only about 1-2 % of that of the sun, hardly a cause of concern in that respect.
A few lamps clearly stand out from the rest with their almost total lack of ultraviolet light. Of these, True-Light lamps are obviously not UV lamps, although their retailer has sometimes recommended them for this purpose. The lamp models Repti Glo, Life-Glo, Exo-Terra Repti Glo 2.0, and ESU Reptile Super UV Daylight, emit only a few percent of their radiation in the UVA range, with even less in the UVB range. Active UVHeat lamp also stands out with its rather low percentage of UVB radiation; This is, however, a bit misleading, since the nominal power of this lamp is significantly higher than that of any other lamp. Although its irradiance in UVB region is quite high, this is still not a proof of its high capability to promoting photosynthesis of vitamin D3, as shown later.
When evaluating the proportion of UVB radiation only, Zoo Med ReptiSun 5.0 and Sylvania Reptistar stand out. Over 6 % of their total irradiance is in the UVB range. Narva Reptilight and R.C. Hagens Exo-Terra Repti Glo, models 5.0 and 8.0, make up another group with their 3-4 percent UVB proportion. The rest of the lamps produce only extremely small amounts of UVB.