A clean filter would allow one to see light poking through the 'pores' of the filter whereas a dirty filter would block out the light entirely.

一个干净的过滤器将允许一个人看到戳通过光的毛孔的过滤而肮脏的过滤器可以堵住了灯完全复原了。

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The results of a series of permeationexperiments prove that the permeation rate of clean filter media decreases with thepermeation time increaese.

过滤介质的透水实验表明，清洁过滤介质的透水速率随时间延长而降低。

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Before treating, let any suspended particles settle to the bottom, or strain them through layers of paper towel, clean cloth, or coffee filter.

在处理前，让任何悬浮物沉淀到底，或用多层纸巾、干净衣服或咖啡滤器把它们过滤掉。

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In case you don't have your smartphone app handy, the taps are equipped with LED lights to show the water's filter status as well -- blue means clean, yellow means not so much and red means you should probably get a new filter, pronto.

ENGADGET

The "teabag" isn't the only interesting filtration tech on the horizon, and researchers in California are developing a filter that uses nanotech and silver to produce clean water.

CNN: Nanotech and 'tea bag' to clean up drinking water

Then, they move on to clean rooms, where the Dragon sensor and new optical low-pass filter are installed.

ENGADGET: After hours at NAB: A closer look at Red's Dragon upgrade operation (video)