The most valuable ultraviolet-B wavelengths of sunlight, 290 to 320 nanometers, are plentiful in summer.
日光中对人最有价值的UVB波长在290至320纳米，夏季较为充足。
2
The body gets most of its vitamin D not from diet but from skin exposed to the ultravioletB radiation in sunlight.
身体获取的大部分维他命D不是从饮食而是靠皮肤曝露在阳光中的紫外线B射线取得的。
3
As skin pigmentation increases, so does the period of exposure to ultravioletB radiation from sunlight needed to synthesise adequate amounts of vitamin d.