The properties of diffuse light in clusters are becoming an independent tool to test the formation of clusters. Comparison between the predictions from large hydrodynamical simulations and observations of diffuse light in real cluster can give information on the particular merging history. Intracluster PNe are particularly valuable in this respect because they are the only component of the diffuse light in clusters whose kinematics can be measured and whose radial velocity distribution can be compared with those from large cosmological simulations.