The present invention includes a modular stair unit, and kit for assembling the modular stair unit, that may be utilized as either a stair tread or stair riser. The modular stair unit includes a body, housing adjoined therewith, and light source within the housing. The body includes a generally planar dorsal surface and a ventral surface and forms a void between the dorsal surface and the ventral surface, which allows light passage. It is preferred that interior surfaces of the housing are fabricated of a substantially diffusive material.