The article "A Systems Approach to Remote Light Sources" describes the use of hollow light guides in a museum [Borg, 1994]:
In one of the large halls at the National Air and Space Museum, full of rockets and satellites, changing lamps and maintaining the luminaires in the ceiling always were very expensive and time-consuming tasks, and thus much neglected.
Here, the 94 high-intensity discharge (HID) lamps have been replaced by three sulfur-lamp units used in combination with three 30-m hollow light guides ("light pipes"). These light pipes are internally clad with a highly reflective optical film that transports and distributes the light evenly towards the floor from over their entire length. Each sulfur lamp unit feeds light into a pipe from an easy-to-access catwalk at the side of the room. The rail-mounted pipes are divided into three sections and can be rolled back to the catwalk for cleaning and repair. The system offers improved color and reduced shadowing. Moreover, unwanted UV radiation was cut by half, an important feature for a museum.
The efficiency of hollow light guides is a much-debated issue: The above installation appears to be very efficient, with lighting levels increased three-fold and energy use cut by 1/3. Although a modern HID-lamp system also would have increased efficiency, the maintenance problems would have been the same, with the luminaires getting more and more dirty. Here, it appears that it is the combination of efficient light distribution (the light pipes in this case both transport the light over a long distance and distribute it evenly) and the easy-to-maintain feature that accounts for the savings.
A similar explanation also must be sought at the U.S. Department of Energy's Headquarters (the Forestall Building) where an 80-meter-long outdoor light pipe installation is fed by one sulfur-lamp unit at each end. These two lamps replaced ~240 old luminaires with 175-W, conventional, HID lamps. Light levels were increased fourfold, while power requirements decreased by 2/3.
