  The brilliant white appearance of ultrathin scattering media with low
refractive index contrast and the underlying radiative transport phenomena
fascinate scientists for more than a decade. Examples of such systems are the
scales of beetles of the genus Cyphochilus, photonic network structures or
disordered Bragg stacks (DBS). While previous studies relate the highly
efficient scattering in the scales to the anisotropy of the intra-scale network
and diffusive light transport, the coherent radiation propagation dynamics
remained unaccounted for. Here, we identify different coherent light transport
regimes using time and spatially resolved coherent light scattering
spectroscopy. At least 20% of the collected scattered light originates from
weakly localised random photonic modes, in contrast to solely diffusive light
transport assumed to date. The identification of this significant role of weak
localisation in ultrathin brilliant scattering media establishes a new design
paradigm for efficient scattering optical materials.
