Lighting systems and devices include a light-transmissive tube and a light source assembly. The light-transmissive tube defines a cavity that extends along a longitudinal axis, at least a portion of the tube having an inner structured surface facing the cavity, and an outer structured surface facing away from the cavity. The light source assembly is disposed to inject light into the cavity, and includes one or more discrete light sources such as LED sources. The inner and outer structured surfaces of the tube are configured to direct a first portion of the injected light out of the tube through the outer structured surface and to direct a second portion of the injected light back into the cavity, such that a virtual filament, or pattern of virtual filaments, appears in the tube.