  When waves scatter multiple times in 3D random media, a disorder driven phase
transition from diffusion to localization may occur [Anderson 1958 Phys. Rev.
109 1492-505; Abrahams et al 1979 Phys. Rev. Lett. 42 673-6]. In "The question
of classical localization: A theory of white paint?" P.W. Anderson suggested
the possibility to observe light localization in TiO$_2$ samples [Anderson 1985
Phil. Mag. B 52 505-9]. We recently claimed the observation of localization
effects measuring photon time of flight (ToF) distributions [St\"orzer et al
2006 Phys. Rev. Lett. 96 063904] and evaluating transmission profiles (TP)
[Sperling et al 2013 Nat. Photonics 7 48-52] in such TiO$_2$ samples. Here we
present a careful study of the long time tail of ToF distributions and the long
time behavior of the TP width for very thin samples and different turbidities
that questions the localization interpretation. We further show new data that
allow an alternative consistent explanation of these previous data by a
fluorescence process. An adapted diffusion model including an appropriate
exponential fluorescence decay accounts for the shape of the ToF distributions
and the TP width. These observations question whether the strong localization
regime can be reached with visible light scattering in polydisperse TiO$_2$
samples, since the disorder parameter can hardly be increased any further in
such a "white paint" material.
