“我觉得我亮眼的新42毫米手表的手腕监测功能有问题,一名使用者写到。“屏幕一黑手表就锁上了,并提示我输入密码。我收不到通知。手表并没有与皮肤失去接触,所以我弄不清原因。网上也没有人提出同样的问题。我打算放弃并且给Apple公司打电话。我的左臂上有纹身,戴手表的位置也有。我试着把手表拿在手里,它就可以正常使用了。我的手上没有纹身,手表就一直处于开启状态。一旦我把它放在有黑色纹身的地方,它就又自动锁上了。
As a possible explanation, another Redditor writes that:
一位网友给出了较为合理的解释:
“Oxyhemoglobin has several local peaks of absorbance which can be used for pulse oximetry: one green, one yellow, one infrared, etc. Apple uses the ones at infrared and green parts of the spectrum. Now, here’s some key facts. Melanin and ink are both equally good at absorbing frequencies over 500nm, which sadly includes the green. But, melanin’s absorbance falls down so rapidly that by the infrared end of the spectrum its hardly absorbing anything at all. That, combined with the fact that Apple adjusts the sensitivity/light level dynamically means infrared is probably black people friendly. Ink has a much more gradual fall off, so even infrared might not work for them.
“氧基血红素能快速吸收绿光、黄光和红外光等,可用于脉搏血氧测量。苹果公司就利用了其可吸收光谱中的绿光和红外光的性能。现在,有几个关键原理。黑色素和墨水都易于吸收频率高于500纳米的光,可悲的是,这其中就包括绿光。但是,黑色素的吸光度下降迅速,到光谱红端它几乎什么都不能吸收了。再加上手表能不断地调节感光度,这就意味着红外光可能对黑皮肤较为友好。而墨水的的吸光度下降平缓,因此连红外光也无法为其工作了。
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