Here is another example of something which is -- this is a little spectrophotometer. It measures the absorption of light in a sample The neat thing about this is, you have light source that flickers on and off at about 1,000 hertz, another light source that detects that light at 1,000 hertz, and so you can run this system in broad daylight.
这里 还有个关于分光光度计的例子 分光光度计是用来测量光度吸收率的一种仪器。 这一仪器使用的前提是， 你需要有一个以接近1000赫兹闪动的光源 和另一个用来检测频率在1000赫兹光波的光源。 然后你即使在白天也可以使用这个仪器