The glass dome was also designed by Foster to be environmentally friendly. Energy efficient features involving the use of the daylight shining through the mirrored cone were applied, effectively decreasing the carbon emissions of the building.
Foster's dome is a gleaming metal and glass structure with a ramp that spirals up a to a roof terrace with 360-degree views of central Berlin. The dome overlooks the debating chamber for the Bundestag and a central mirrored cone together with a large sun shield tracks the movement of the sun electronically and blocks direct sunlight which might bedazzle those below.
In Fostner's words:
“As well as forming the public focus of the building, the Reichstag’s cupola, or ‘lantern’, provides the key to our strategies for lighting and ventilating the assembly chamber. At its heart is a light-reflecting cone – a light ‘sculptor’ and a sculpture in its own right. The cone is covered with faceted mirrors that together form a giant Fresnel lens just as you might find in a searchlight or a lighthouse. In fact the cone works as a lighthouse in reverse, reflecting daylight from a 360-degree horizon down into the chamber. An electronically controlled mobile sun-shade tracks the path of the sun to block solar gain and glare, but is designed to allow a little sunlight to dapple the floor of the chamber. In ventilation terms the cone and chamber together perform as a solar chimney, drawing air up naturally through the chamber and expelling it via the open top of the cupola. In ecological terms, the Reichstag has shown how public buildings can challenge the status quo: big buildings do not have to be big consumers of energy or big polluters. And although it represents a minuscule first step in terms of the journey yet remaining, imagine the impact these strategies could have is they were applied more widely around the world.”
The gallery can be seen here.