Light tubes or light pipes are used for transporting or distributing natural or artificial light. In their application to daylighting, they are also called solar tubes, solar pipes, daylight pipes, or solar light pipes.
Generally speaking, a light pipe or light tube may refer to:
a tube or pipe for transport of light to another location, minimizing the loss of light;
a transparent tube or pipe for distribution of light over its length, either for equal distribution along the entire length (see also sulfur lamp) or for controlled light leakage.
[b]Light tube with reflective material/[b]
Also known as a 'tubular skylight', this is the oldest and most widespread type of light tube used for daylighting.
A round tube lined with highly reflective material leads the light rays through a building, starting from an entrance-point located on its roof or one of its outer walls. A light tube is not intended for imaging (in contrast to a periscope, for example), thus image distortions pose no problem.
The entrance point usually comprises a dome (cupula), or alternatively a diamond-shaped light collector, which has the function of collecting and reflecting as much sunlight as possible into the tube.
Light transmssion efficiency is greatest if the tube is short and straight. In longer, angled, or flexible tubes, part of the light intensity is lost. To minimize losses, a high reflectivity of the tube lining is crucial; manufacturers claim reflectivities of their materials, in the visible range, of up to 98 to almost 99.5 percent.
At the end point (the point of use), a diffuser spreads the light into the room.
To further optimize the use of solar light, a heliostat can be installed which tracks the movement of the sun, thereby directing sunlight into the light tube at all times of the day as far as the surroundingsī limitations allow, possibly with additional mirrors or other reflective elements that influence the light path. The heliostat can be set to capture moonlight at night.