Absorption efficiencies (“emissivity modification factors”, see text for explanation) of dust in the Kelsall model determined for the COBE DIRBE wavelengths by Kelsall et al. (1998), gray area on the plot, and for the Planck HFI wavelengths by Planck Collaboration XIV (2014). Fixsen & Dwek (2002) have also used the data from the COBE FIRAS instrument to determine the annually averaged spectrum of the zodiacal cloud plotted here with a dotted line.