Skylights fall under three categories — skytubes, skylights and roof windows. Skylights come in two basic shapes — square and rectangular or round. Recent innovations include reflective shaft materials, which appeared in the early 90s and enhanced the performance of any size of skylight.
Skytubes are the smallest and around 260 mm in diameter, up to around 400 mm in size. They are shaped like a dome and let in a small amount of light through a reflective light-carrying system and are most suitable for task lighting in areas such as bathrooms, ensuites and hallways.
“The light enters the dome and is reflected down the tube, so it bounces down the light-carrying system. With each bounce of light, you do lose some light — it gets absorbed into the material itself. So if you use an anodised aluminium, the light delivery at the end wouldn’t be as good as using a highly specular silver material,” says Michael Bonello, managing director of Skydome.
Traditional skylights start at around 500 mm2, reaching sizes of up to 2.4m by 2.4m. They usually have a zincalume base with an acrylic or polycarbonate dome. Bonello says it works on a diffuse light principle, versus the skytube, which works on specular reflectivity. “So the light-carrying system is actually built by the installer and it’s usually made from custom wood or it can be gyprock. The light well can be splayed out or it can come straight down to the ceiling below.”
The third category is the roof (or sky) window — basically a window in the roof. Windows can be openable or fixed and are most suited to attic-type rooms. Beezeway’s Fakro product is a sealed double glazing insulating unit which comprises layers to reduce heat gain. On the inside, a double pane of 3 mm glass that has a 0.76 mm laminated interlayer provides 96.7 per cent UV protection, fade and noise reduction.
The laminated safety glass on the interior helps to reduce solar heat gain. It also has a low E coating to reduce heat gain and heat loss through the skylight. This is followed by a 14 mm argon gas filled cavity for increased thermal performance. Lastly, there is a 4 mm toughened safety glass on the exterior for strength and durability.
Natural light from skylights was previously confined to spaces with direct access to the roof. However, Solatube’s Daylighting System works by filtering light from a dome on the roof through an internal reflective system. Tubing to lower levels is installed between rafters, with no need for structural modification. A diffuser then spreads light evenly throughout the room. The system is most suitable for areas where a traditional skylight would not be an option. Depending on the model, the Daylighting System can provide light up to 46m2 in a residential application. It also filters out 99.9 per cent of UV light.
Skydome is developing a similar product. It has been working on a new technology for several years, which works on the basis of a collector being placed on the outside north facing surface of a building, such as a wall or roof. The collector is about 300 mm wide by around 1,200 mm long and captures light and transfers it into a connector. The connector is attached to fibre optic cables, so light can be delivered to the inner core of the building.
The DayRay system is designed to fit into a standard downlight fitting which sits on the ceiling. This means standard light fittings can match the room’s décor. Most standard downlight fittings are screwed into place or clipped into the gyprock ceiling.
“The DayRay collects natural light which goes through a series of colours — basically the [colour] spectrum. When the light passes through one colour, it’s absorbed and transferred to the next colour, absorbed and transferred to the next colour, and it makes its way to the end of the collector and transferred to the fibre optic cable. We’re producing natural white light,” Bonello says.
The fibre optic cables measure 20 mm in diameter and there are four fibres per system. The maximum length of each fibre is 6m. To fit the cables into an existing building, the fibres are fed through the building’s cavities, roofspace or wall cavity, with an access cavity of 50 mm in diameter to the roof space all that is needed per fibre.
Skydome also sells a similar product by Swedish company Parans. Where the DayRay has no moving parts and does not rely on direct sunlight, the Parans unit is a moving system where a series of collectors are built within a frame and move and trap sunlight all day long.
The DayRay is yet to be released, but Bonello expects it will be launched in the next six months. He expects it will cost between $1,500 and $2,000, based on 6m of cable, with the final price dependent on the distance between the collector and the emitting light source.
Traditional skylights cannot measure heat-gain or heat-loss, making quantifiable energy savings difficult to calculate. This meant they could not be used in rating programs such as Green Star. But products such as Solatube’s Tubular Daylighting Devices (TDDs) can measure quantifiable energy savings. Mark Peall, general manager at Solatube, says up to 95 per cent of artificial lighting costs in a commercial application can be saved. He says in addition to double glazing, skylight products need to be fully sealed to aid in energy savings. “Solatube TDDs are designed not to need structural change and can be fitted in under two hours.”
Liz Creagh, product manager — skylights and access ladders at Breezeway, says skylights are energy rated in accordance with the Window Energy Rating Scheme (WERS) to aid the design of energy efficiency in housing. “The amount of ‘shading’ in the window will affect the amount of radiant heat passing into the building. This is measured as the solar heat gain co-efficient. Determining what is a good number is not straight forward. Basically the lower the number, the higher the shading effect. So in summer you will want more shading to stop the summer sun and in winter you want less shading to let the summer sun in and reduce the need for artificial heating.”
Opening skylights can also allow built-up heat in the home to escape through the opening and fresh, cool breezes to flow in to reduce household temperatures. “For Fakro opening skylights, you get a high solar heat gain coefficient number of 0.56 than for fixed skylights with a reading of 0.52,” Creagh says.
Peall says the larger the skylight the greater the heat gain, while designers also have to abide by standards which dictate spans and glass thicknesses. He says currently, there is only one accepted test for rating skylights and roof windows by the National Fenestration Rating Council (NFRC) in the US. “The Australian government has instructed that the NFRC testing protocols must be followed in Australia. At the moment there is only one skylight that has been tested to the NFRC requirements and that is the Solatube Brighten Series.”
