A skylight shaft substrate has a film or coating on its inside surface that reflects visible light while transmitting IR to the tube substrate, which can have a satin black and/or other IR absorbing interior and anodized or other high emissivity exterior to convey heat across the tube so that light is transmitted down the tube but heat transmission is directed through the tube to minimize heating the illuminated space. Or, heat may propagate up through the tube and exit through a clear plastic dome covering the tube.