A skylight tube is a tube (obviously!) of a semi-flexible corrugated material, eight to twenty inches in diameter, with a reflective lining. It runs down through the roof into the ceiling, and a light diffuser shows on the ceiling and clear dome on the top end sticks up through the roof.
The major advantages of a installing a skylight tube instead of a standard flat skylight are its low cost, simple DIY installation, and its energy efficiency. Since it is relatively small in diameter and the entire tube forms a sealed area of dead-air space, there is little energy loss as compared to a conventional skylight.
We installed two of these skylight tubes in our shed/garage last autumn, and the results were reasonable for the low price. While it only helps out in daytime applications, I find I can do more work out in that shed without flipping the switch for the lightbulb very often, even on cloudy days. The light has a funny hue to it, which takes a while to become accustomed to, but again, the savings on electricity are worth it. I might personally suggest a full conventional skylight for more classy indoor applications, but I guess it could do a great duty to a cottage or summer house. The installation took us approximately an hour and a half, although YMMV.
The most popular brand name for this product seems to be Sola-Tube, an Australian product. We grabbed ours from Home Depot in Canada, and to be totally honest I don't remember the brand name, but it wasn't Sola-Tube.