its foregrounds, and so it was very difficult to observe. Later the discovery and observations of high luminosity infrared galaxies in the vicinity of the Milky Way showed, that the peak of the CIB is most likely at longer wavelengths (around 50um), and its full power could be ~1-10% of that of the CMB.

As Martin Harwit emphasized, the CIB is very important in the understanding of some special astronomical objects, like quasars