Limber equation for luminosity dependent correlations

The passage from angular to spatial correlations, in the case of spatial cl ustering length depending on the average distance between nearby objects is studied. We show that, in a number of cases, the scaling law of angular co rrelation amplitudes, which holds for constant spatial clustering length, i s still true also for a luminosity dependent spatial correlation. If the Li mber equation is then naively used to obtain 'the' spatial clustering lengt h from the angular function amplitude, a quantity close to the average obje ct separation is obtained. The case of cluster clustering is explicitly con sidered. (C) 1999 Elsevier Science B.V. All rights reserved.