Can you explain how that works? As I understand it, UVB is responsible for both vitamin D synthesis and skin damage. So how is it then possible that 1 minute of sun-lamp radiation is equivalent to 15 minutes of natural/sun radiation in terms of vitamin D, but not in terms of skin damage?

I was talking about tanning and burning. That is UVA. Vitamin D lamps limit the light to a single wavelength at least mine does. As for damage, the wavelengths that are suppose to cause the most damage are different to the wavelength that it uses for vitamin d.

Ok thanks, one more question, for the curious.. whenever I've seen people use these lamps, they are pointing them to their face (maybe because of winter mood/blues etc.).

Would these lamps be more effective if they pointed the lamps towards exposed arms/legs (greater surface area)?

I point it at my torso, wear glasses (they came with the device) and have closed eyes for the duration. I have no idea why anyone would point it at their face.