A Lambertian emitter is a device that emits light in all directions. This is in contrast to a laser, which emits light in a single direction, or an LED that emits light in a narrow cone. Incandescent lights (including neon, fluorescent (I lump this type in with the rest because the light is created by an excited gas which then causes the phosphor in the tube to glow), and noble gas), OLEDs, electroluminiescent material, fire, and objects glowing from heat are all examples of things that emit light in all directions.