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Old 11/24/2013, 08:09 PM   #47
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Join Date: Feb 2007
Location: Santa Monica, California, USA
Posts: 2,451
Really neat pic of the "pupil". One thing that comes to mind that uses the same technique is the traffic light sensor; it has a tube that points at oncoming cars, and only when the headlights are shining down the tube do the lights change.

Inventor of the easy-to-DIY upflow scrubber, and also the waterfall scrubber that everyone loves to build:
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