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This is pretty cool. It looks like the cost of LEDs is by far the largest blocker to scaling this or making it a consumer product (if that's even intended). I suspect it's because they're esoteric frequencies are high precision. Is this precision needed to discriminate between different plastics or does it just increase the accuracy of a match?

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i work with IR emitters (LEDs) (similar to this project but with several cameras), in the SWIR range a single LED can easily cost 10-20$. they tend to have very low efficiency at these wavelengths too, typ around 1mW/sr (120 degrees) at 50mA. a good SWIR setup with a camera and led illumination will quickly be 20-50k.

Sorry if I'm misinterpreting your comment but are you implying that this project is snake oil?

I guess what he is implying is, that the LED is the biggest cost factor on the BOM of such a product. If you have the goal of making such a product available to every household, would it be a feasible product if the bill of materials is say 40 USD already? How much would people pay for such a thing?

Of course in electronics everything gets massively cheaper with scale.

not at all, was just saying LEDs in these wavelengths are terribly expensive, very cool project

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