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Tubular skylights are special skylights that require minimal carpentry skills to install. Instead of cutting a large hole in the roof and the room's ceiling, with the associated framing needed to make a drywall box between the two, a tubular skylight requires smaller holes and no framing. Instead the roof lite and the ceiling lite are connected with a reflecting flexible shaft.
I have seen these "in action" and my impression is that they are a great way to add "free" natural light to an otherwise dark area of the house, such as an interior bathroom, hallway or closet. They can also be used in rooms but depending on the room size… more than one might be called for to get the correct lighting effect.
When making your decision, keep in mind that a regular skylight will supply more light because it is physically larger. To get more information on dimensions, the best resource I know of on the Web is a manufacturer's site... Velux Sun Tunnel at http://suntunnelskylights.veluxusa.com.