  Aims. We here demonstrate how the recently developed Lightweaver framework
makes non-LTE (NLTE) spectral synthesis feasible on a new 3D ab-initio
magnetohydrodynamic (MHD) filament/prominence simulation, in a post-processing
step. Methods. We clarify the need to introduce filament/prominent-specific
Lightweaver boundary conditions that accurately model incident chromospheric
radiation, and include a self-consistent and smoothly varying limb darkening
function. Results. Progressing from isothermal/isobaric models to the
self-consistently generated stratifications within a fully 3D MHD
filament/prominence simulation, we find excellent agreement between our 1.5D
non local thermodynamic equilibrium Lightweaver synthesis and a popular
Hydrogen H{\alpha} proxy. We compute additional lines including Ca~\textsc{ii}
8542 alongside the more optically-thick Ca~\textsc{ii} H&K & Mg~\textsc{ii} h&k
lines, for which no comparable proxy exists, and explore their formation
properties within filament/prominence atmospheres. Conclusions. The versatility
of the Lightweaver framework is demonstrated with this extension to 1.5D
filament/prominence models, where each vertical column of the instantaneous 3D
MHD state is spectrally analysed separately, without accounting for (important)
multi-dimensional radiative effects. The general agreement found in the line
core contrast of both observations and the Lightweaver-synthesised simulation
further validates the current generation of solar filaments/prominences models
constructed numerically with MPI-AMRVAC.
