Tubular skylights provide an easy way to bring natural light into your home. They channel daylight from an aperture on the roof down through your attic to your ceiling. Daylight is transmitted through a cylindrical tube 8 to 24 inches in diameter with a highly reflective interior surface. A translucent diffuser, mounted on your ceiling, looks much like a conventional light fixture.
Today there are more than a dozen companies producing tubular skylights. Tubular skylights usually have plastic domes on the roof. Some tubular skylights also have scoops or prisms to enhance light collection. Special roof flashing kits, to seal the skylight to the existing roof, are available to adapt the units to various slopes and types of roofs.The skylights’ reflective tubes have a highly reflective silver film or highly polished anodized aluminum surface on their interior to channel the daylight downward. Each reflective surface has advantages and disadvantages. Reflective silver films have the highest reflectivity, but may eventually delaminate. Polished aluminum doesn’t delaminate, but the surface can oxidize with age, reducing its reflectivity.
Most ceiling diffusers are white acrylic, which spreads the light fairly evenly. A few products have prismatic diffusers, which spread the daylight farther into the room where they’re installed.
Most residential tubular skylights cost $300 to $500, excluding installation. Their light delivery varies according to the outside sunlight conditions, the diameter of the tube, the transparency of the exterior dome, the reflectivity of the tube inner wall, and the transmittance of the ceiling diffuser.
Light tubes make the most sense in dark areas of the home, away from windows, where you would otherwise use electric lights during the day. Light tubes in home locations where you normally use only an hour or two of electric lighting per day (such as bathrooms and closets) may take decades to pay back. But, in any location they can improve the livability of your home by providing cheerful outdoor light.
Residential Energy contains extensive information on lighting energy efficiency.