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Comment by Animats | Hacker News Reader

They've developed a photonic crystal [1] which reflects IR while passing visible light. That should be useful. Using it to to try to reflect IR back to the filament of an incandescent bulb is probably not going to be cost-effective. Photonic crystals have detailed structure like an IC, with waveguides and cavities, and are made by similar methods. That's a lot to make just to get an IR mirror for a light bulb, since you'd need a large surface area of the material. Probably more expensive than fabbing LEDs.

This sounds like an interesting development overhyped by the PR staff. Again. See [2].

[1] http://ab-initio.mit.edu/photons/ [2] https://news.ycombinator.com/item?id=10916894

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Nah, I bet this can be done with a 1D photonic crystal where they can get away with simply using alternating layers of uniform thin film thickness. I forget exactly but I'd think all that's needed is alternating dielectric constant materials with a periodicity ~700nm which isn't that crazy. More expensive than glass sure, but it's not like it'll need special etching to get microlenses.

FWIW, slide 21 from this presentation on the site you linked has the picture I have in mind since at that size scale the glass is effectively flat.

http://ab-initio.mit.edu/photons/tutorial/L1-bloch.pdf

Feel free to correct if this is oversimple, I am vaguely familiar with this stuff but it was by no means a speciality.

That sounds like an ordinary bandpass interference filter.[1] Those have film layers and only pass a specific wavelength of light. Unlike ordinary filters, the angle at which the light hits the filter affects the passband, because it's the spacing of the layers that makes it work. The receive side of LIDAR systems use those. But those absorb the light they reject; they don't reflect it, much.

[1] http://www.edmundoptics.com/optics/optical-filters/bandpass-...

Gotcha, that makes sense. I suppose most of it will come from a narrow solid angle so if it were perfectly spherical you'd be okay but that would only work for the first reflection unless it was all reflection and no emission...

It reminds me of the halogen infrared (HIR) bulbs used for automotive lighting. I'm not clear on what advantage a theoretical mass-produced photonic crystal bulb would offer for this application that HIR does not. Any thoughts?

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