The Yomiuri Shimbun (newspaper)
YOKOHAMA--Look through the glass ceiling in the third-floor lobby of the Minatomirai Center Building in Nishi Ward, Yokohama, and you'll see nothing else between you and the sky--there is a huge, uncovered atrium in the middle of the 21-story, 100-meter-high building.
With 18 stories worth of building surrounding the space on all sides, however, a solution was needed to channel sunlight through the passage to prevent it from being a dark, shadowy hole.
An automatic solar light-tracking system is that solution. The system uses mirrors that, by adjusting their position relative to the movement of the sun, reflect sunlight from one to the next, sending rays all the way down to the third-floor lobby.
"The sunlight is taken full advantage of, from morning to evening. The system means 20 percent less electricity is needed to illuminate the corridors around the atrium," said Yuichi Minemura, 42, a senior architect with Taisei Corp. who worked on the construction of the building, which was completed in May.
The higher a building is, the less exposure its lowest floors have to direct sunlight. Taisei came up with the mirror system as a way to solve the problem.
The primary mirrors are fixed to the roof, facing skyward, and automatically adjust their angle as the sun moves across the sky to fully face its rays.
Sunlight is reflected from the primary mirrors to secondary mirrors, which are fixed in a higher position, facing down into the 18-story atrium.
Inside the atrium, long, narrow aluminum mirrors are attached to the walls. These mirrors' surfaces are not smooth, but rather covered with many tiny projections that diffuse the natural light to each floor below.
There are 16 primary and 16 secondary mirrors on top of the building. Each is round, with a diameter of 1.2 meters.
The building obtained an S Rank, the top grade, in a Yokohama program to rate buildings' eco-friendliness.
The system reduces the need for electric lighting, and the open atrium well allows heat to escape from inside the building, meaning a heavy-duty ventilation system is not required.
Thanks to those benefits--along with a variety of other energy-saving efforts, such as a rooftop garden and heat-shield windows--the building's CO2 emissions are about 30 percent less than most buildings of the same size.
The design is beneficial on an environmental level, but also a human level.
"People can feel relaxed when they see a bright open space," Minemura said, adding that he is continuing to explore new ways of adapting sunlight.
"Using natural light means more than just conserving energy," he said.
