an office worker reaches up to replace a long glass tube in the ceiling-mounted fluorescent light fixture. The worker carefully inserts the tube into the fixture as it begins to flicker to life. Mercury vapor inside the glass tube glows as electricity flows through it, creating the characteristic white light. The phosphor coating on the inside of the tube transforms the energy into bright illumination. A coworker holds a ladder steady while watching the tube produce its steady, even light across the workspace. Office desks and equipment become clearly visible under the artificial fluorescent glow. how fluorescent lights produce illumination by passing electricity through mercury vapor in a phosphor-coated glass tube