  CELES is a freely available MATLAB toolbox to simulate light scattering by
many spherical particles. Aiming at high computational performance, CELES
leverages block-diagonal preconditioning, a lookup-table approach to evaluate
costly functions and massively parallel execution on NVIDIA graphics processing
units using the CUDA computing platform. The combination of these techniques
allows to efficiently address large electrodynamic problems ($>10^4$
scatterers) on inexpensive consumer hardware. In this paper, we validate near-
and far-field distributions against the well-established multi-sphere
$T$-matrix (MSTM) code and discuss the convergence behavior for ensembles of
different sizes, including an exemplary system comprising $10^5$ particles.
