A while ago I made a project that displayed the fastest route home based on live traffic conditions using Google Maps. It used through hole neopixels to display each route. Some feedback from that project was "wouldn't it be cool if the entire route lit up rather than just LEDs along it". That suggestion led me to light pipe but I never got a chance to try it out.
Light pipe is a transparent pipe that illuminates when you shine a LED in either side of it. I bought mine from Aliexpress as light up shoe laces, a pair is about $2 delivered*.
The LEDs I used are 5mm, clear, through hole addressable LEDs, I believe I bought them as APA106 (PL9823 is another common through hole addressable LEDs). I can not find any clear LEDs like this in any of the usual places, but I did find some on Sparkfun.
I'm using a 3D printed part to hold the LEDs and the light pipe together, I designed these in Thinkercad. The Thinkercad part also includes some of the intermediate pieces for making it up, so it is a useful base if you wanted to use it as a template for another project. It's also available on Thingiverse.
I was really happy with how this turned out! For more details check out the video on YouTube:
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