Average luminosity of night sky vs frequency.... What is the average luminosity of the night sky in all observable wavelengths, from the shortest down to the longest? Are there estimations/approximations anywhere of average luminosity plotted against wavelength? Are there links to papers that anyone can offer? The common words that I use to Google this question give far too many results, almost entirely irrelevant. The reason I ask this is an interest in "tired light". If cosmological redshift is not a function of universal expansion, and is instead a function of the interaction of EM with the fields through which it propagates (yes, I'm still modeling those pesky ZPE fields!) we should expect that a static infinite universe will have an almost isotropic luminosity at the very longest wavelengths. The absence of isotropy at the longest wavelengths would falsify, or at least seriously constrain a tired-light model in an infinite universe. What's more, if redshift by ZPE field interaction is wavelength-dependent (energetic, short-wave EM interacts more strongly and is redshifted more than longer wavelengths), there should be a discernable rise in luminosity as wavelengths increase, since longer wavelengths will be "selected for" by the mechanism of interaction. I envision an Olber's paradox type effect, in which the background of the universe might be quite luminous, but at VERY long wavelengths.