Solar tube skylights (also called sun tunnels, sun tubes or tubular skylights) are an excellent alternative to traditional skylights and roof windows. If you aren't interested in views or ventilation, only in natural lighting, consider solar tubes instead of common glass (or plastic skylights).
1) a dome, to capture the sunlight;
the dome is mounted on a metal flashing system designed to provide optimal angle for the gathering of solar light and to prevent water infiltration;
2) a light diffuser, mounted on the ceiling of the room, to supply the light captured by the dome; the light diffuser is attached to a ceiling ring;
3) and a tunnel, that is, a “pipe” connecting the dome to the diffuser; the tunnel is made from a highly reflective material, able to provide a brighter and whiter light output.
Image credit: Energy Star.
The light collector (typically an acrylic lens in a metal frame) is typically parabolic. Many sunlight tubes have baffles to control the amount of incoming sunlight, and also electrical lights to provide lighting at night…
They can use either flexible or rigid metal reflective tubes. Flexible tubes are great for attics involving obstructions, but rigid tubes provide more lighting.
solar tubes advantages
Solar tube skylights can provide as much natural light as traditional skylights, without being a cause of heat loss in the winter, or overheating and excess light in hot weather conditions.
They provide diffuse and indirect natural light, and they look like a common lighting fixture.
Solar tube skylights are small devices, relatively easy to insulate and air seal, contrary to traditional skylights.
The light diffuser may have a UV coatings to filter out UV rays, important to avoid furniture fading and other similar effects of UV radiation.
Their redirected sunlight can help people suffering from seasonal affective disorder – associated with insufficient natural sunlight.
Solar tubes disadvantages
Solar tubes do not provide views, or ventilation.
Like other skylights, they only are effective at illuminating the upper floor of multi-story buildings. Long reflective tubes will reduce their effectiveness; to overcome it, solar tubes should be mounted in areas receiving unobstructed sunshine during large periods (units installed in areas receiving direct sunlight will provide more lighting).
Solar tube prices and warranty advantages
Expect prices around $150-$300 for very basic models. Larger and more sophisticated units can cost $600, or more.
Lifetime warranties are common. Demand at least a 10 year warranty. Tubular skylights are now a tested technology, and are part of the offer of most skylight manufacturers, including Velux, ther undisputable world's leader.
Solar Tubes - Installation advantages
Installing a solar tube skylight is easier than installing a traditional rectangular skylight. To install the three parts of the solar tube, you will “just” have to...
1) cut two holes, one in the ceiling and one in the roof deck;
2) place the diffuser ring around the ceiling hole:
3) install the roof flashing around the hole in the roof;
4) connect the flashing to the diffuser ring by installing the tube system;
5) mount the dome on the metal flashing system;
6) mount the diffuser in the ceiling ring.
Sun tunnels are lightweight structures that usually fit between the trusses without the need of any reinforcement or modification in the roof system, but you have to confirm it, and to consider carefully the exact positioning of the sun tunnel, according to the room and the place where you want to install the light diffuser.
You should select the most advantageous spot between the ceiling joists and roof rafters, without forgetting electrical wiring, ducts or other obstructions…
Choosing a spot where the tunnel follows a straight run makes the installation easier and provides more daylight. Otherwise you will need elbows or flexible skylights (with a flexible tube), to be installed around attic obstructions.
You should also consider the exact type of solar tunnel and its dimensions. Typically, rigid tunnels provide more light and are a better option than flexible tunnels, and unless there is obstacles in the attic you should prefer them.
The size (diameter) of the system, say, a 10’’ (25 cm) or a 14’’ (35 cm) or a 21’’ (53 cm), is also an important issue. The wider diameters provide more light (some manufacturers recommend a 10’’ diameter for rooms up to 200 sq. feet, and 21’’ for rooms close to 325 sq. feet, but in practice it depends a lot on how much light you need).
The type of roof (“pitched”, “low profile”...) and roof covering (shingle, asphalt, tiles…), or the pitch of the roof (between 15º and 60º…) should also be taken into account, when choosing a solar tube.