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If a Faraday cage’s hole size determines the wavelength of light which can penetrate it then I would imagine this would be possible.

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  • $\begingroup$ Nothing easier than this: en.wikipedia.org/wiki/Optical_filter#Bandpass. To let through separate wavelengths, say IR and UV, one need two filters and holding them one behind the other cancel out both wavelengths. But to have a broad filter = Bandpass and to let throught some wavelengths from .. to .. is possiblean din optics well done. $\endgroup$ Jul 8, 2016 at 17:21
  • $\begingroup$ @HolgerFiedler But I could interpret this as only asking for a long-wave cutoff filter, so a screen -type filter in this case is theoretically possible. (tho' with a lousy cut-off slope $\endgroup$ Jul 8, 2016 at 17:44

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The blue end of the spectrum is higher frequency, meaning shorter wavelength. A cage that can block blue is going to block (technically attenuate) the given wavelength and any that are longer (lower frequency). If you start blocking at blue, you'll be blocking the entire visible spectrum and on down into the IR, microwave, and radio.

To filter out UV, the mesh would have to be so fine that it easily blocks everything below it, including the entire visible spectrum.

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  • $\begingroup$ Just to make this post more complete: there are methods (not Faraday cage) for filtering high frequency radiation while allowing lower frequencies to pass through, most rely on material science concepts. Sunscreen is an example of a substance which blocks high frequency light (UV) and allows visible light to pass. $\endgroup$ Jul 8, 2016 at 15:53
  • $\begingroup$ Thanks for your answer. I meant to allow only blue and violet to pass through. Sorry for the confusion. If two polarizing films 90 degrees to each other (effectively a Faraday cage) will not permit visible light through am I correct to believe that increasing the spaces slightly between each polarizing strip in the film would allow only these shorter wavelength colors through? $\endgroup$
    – James
    Jul 8, 2016 at 16:09
  • $\begingroup$ If you want to only allow blue/UV through you still cannot do that with "only" a Faraday Cage. You can us one which blocks everything longer than blue, but you'll need another method as James Rowland suggests to block the shorter frequencies in constructing your "band pass" filter. $\endgroup$
    – alzee
    Jul 8, 2016 at 16:13
  • $\begingroup$ for completeness, there are glass filters e.g. UG11 that transmit in the UV and not visible, as well as interference filters that can be made to transmit at almost any small range of wavelengths you choose as well as numerous compounds, such a CuSO$_4$ that transmit ir and uv but not much visible light etc. $\endgroup$
    – porphyrin
    Jul 8, 2016 at 18:05

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