The Phosphor was an invention of Henry Branwell meant to give off a blaze of light five times more powerful than that of witchlight.

The first time Henry illustrated the device in front of the London Institute residents, the Phosphor turned all the lights off in the dining room. Henry then offered to use the Phosphor as the signal for the Clave to attack Alexei de Quincey's vampire party. It once again malfunctioned and, instead, set the house's furnishings, as well as some of the vampires inside, alight.