Bell Labs demonstrated the first practical silicon photovoltaic cell in 1954, and decades of falling costs made rooftop and field-scale solar power a mainstream electricity source by the 2010s. The efficient white light-emitting diode, enabled by the blue LED of the 1990s, cut lighting energy use sharply for streets, buildings and signs. Together they let buildings and districts generate clean power and light at far lower energy cost. Distributed solar reshapes roofs, facades and the electricity grid.
Cheap solar generation and efficient LED lighting underpin low-carbon, partly self-powered districts and have changed the energy logic of the built environment.