  Technological civilizations may rely upon large-scale photovoltaic arrays to
harness energy from their host star. Photovoltaic materials, such as silicon,
possess distinctive spectral features, including an "artificial edge" that is
characteristically shifted in wavelength shortwards of the "red edge" of
vegetation. Future observations of reflected light from exoplanets would be
able to detect both natural and artificial edges photometrically, if a
significant fraction of the planet's surface is covered by vegetation or
photovoltaic arrays respectively. The stellar energy thus tapped can be
utilized for terraforming activities by transferring heat and light from the
day side to the night side on tidally locked exoplanets, thereby producing
detectable artifacts.
