Parabola has libcl on our blacklist because libcl (Arch version) contains the OpenCL library and ICD loader from NVIDIA (which is not free). Until yesterday, we didn't have a libre version to replace that package. Because of this, luxrays and luxrender were on the blacklist, and replaced by luxrays-libre and luxrender-libre.
But yesterday, Márcio Silva (coadde) released a libre version of libcl called libcl-libre built from Mesa OpenCL source code and due it, now we have libcl support on our distro.
This means that you should install luxrays and luxrender packages manually using regular pacman methods and remove luxrays-libre and luxrender-libre because aren't needed anymore.