Every year the Tate Britain Art Museum commissions an artist to decorate its Christmas tree. Last year's was covered with guns and fighter planes, another was hung upside down and yet another year there was just a note saying the tree had been given to charity. This year's creation by Bob & Roberta Smith has an ecological and recycling theme.
Called "Make Your Own Xmas", it's big, ramshackle wooden structure made of recycled materials, including sandwich boards, tape, signs and an oil drum. Eight bicycles of various sizes have been fixed to stands around the "trunk" (bottom), each holding a generator that is connected to a set of light bulbs that decorate the tree. When happy children and chuckling adults hop on the bikes and pedal hard, the lights go on.