The discovery in the COBE all-sky maps of a bright isotropic background in the far-IR/sub-mm, of likely extragalactic origin (CIRB), with a proeminent hump at a wavelength of 140 μm, has been interpreted at first as the integrated emission by dust present in very distant galaxies (Puget et al. 1996; Hauser et al. 1998). What is the relation between the CIRB and the topic of this Conference, Lighthouses of the universe? In the infrared, the lighthouses are the LIGs ( L_IR ≥ 10^{11}L_&sun; and the ULIGS ( L_IR ≥ 10^{12} L_&sun;). Discovered by IRAS, the LIGs and ULIGs appeal to be mostly powered by star formation, although at least some also harbor an AGN. In the local universe, LIGs and ULIGs together emit less than 10% of the IR light, and less than 2% of the bolometric light. Is their contribution much more important at large distances? Are they ultimately responsible for the CIRB?