This chart shows that vit. D2 production is at it's peak at about 300nm, and drops off sharply between 300nm and 320nm.
This shows: " The vitamin D effective radiation is described in terms of its action spectrum (i.e., the efficiency of each wavelength to synthesize vitamin D in skin) . In broad terms, the action spectrum covers the UVB spectral range with a maximum at about 295 nm (Figure 2)."
"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 (nanometers) promotes photosynthesis of vitamin D3, radiation above 300 nm destroys vitamin D3 that has been already synthesized in skin tissue or obtained nutritionally."
These three studies makes me think that the designation of UVB emitting lamps as between 280-320nm as good for skin conversion to vit.D2, might be false or confusing.
If we don't know conversion rates from 280-200nm, nor the destruction rates between 300-320mn, then a UV emitter that states it produces UV from 280-320nm can't be trusted. The conversion rate must be higher than the destruction rate.
What are we to think? Do I misunderstand study 1.)?