From Destinypedia, the Destiny wiki
Clarity Control is a veiled figure, identical in appearance to those found in the Black Garden, the Lunar Pyramid, and the Europan Pyramid. Unlike these others, which seem to be merely inanimate statues, Clarity Control exhibits slight movement: the lower folds of its cloak move slowly, and its chest region rises and falls in a way that suggests that it is breathing. The figure is suspended in midair, and appears to be surrounded by a forcefield that selectively repels certain objects, such as fallen snow and ice; the tunnel in which it is located suffered a cave-in at some point, but an ovoid volume around the figure remains clear of debris.
Clovis Bray I discovered Clarity Control somewhere on Europa, after the K1 anomaly told Clovis to go to Europa. Clarity Control had a "violent reaction" to Clovis Bray teams attempting to move it. Eventually they did move it, however, and stored it in the Deep Stone Crypt.
Clarity Control was used to combine Darkness (referred to as "Clarity" by Clovis I) with Vex Radiolaria to create Alkahest, a primary ingredient in the creation of the Exo. Clarity Control, in Clovis I's words, is the source of Clarity.