Selenium is a photoconductive substance.    From Wordnet, Princeton University. 

It also displays what is called a photoconductive action, in which electrical conductivity increases as more and more light shines on the selenium.    From Wordnik.com.  [Selenium] Reference

"photoconductive" surfaces, takes only seconds to complete, they note.    From Wordnik.com.  [EurekAlert! - Breaking News] Reference

Each fiber, just one-milimeter in diameter, is made out of a photoconductive glass core, electrodes, and a transparent sheathing.    From Wordnik.com.  [Boing Boing: July 16, 2006 - July 22, 2006 Archives] Reference

It is essentially a Chip Holder which holds up to four THz photoconductive antennas used for generating and detecting THz radiation.    From Wordnik.com.  [Marketwire - Breaking News Releases] Reference

These devices include photodiodes, photomultiplier tubes, scientific light sources, infrared detectors, photoconductive cells, and image sensors.    From Wordnik.com. Reference