Phosphor lamps were used for lighting. They used electron excitation; when shaken, they grew brighter.
The human colony on Frontios used phosphor lamps as their primary light source as they had no electricity. Turlough claimed that the metal casings on the lamps made them a fire hazard. The Fifth Doctor had Turlough and Tegan return to the TARDIS to fetch a better light source as he could not work under the lamps' dull glow.