“The glowing one mumbles something and is then silent. He is drooling uncontrollably.”
Glowing ones or luminous necrotic post-humans are ghouls who have absorbed so much radiation that they glow in the dark. They have become living conduits of radiation to the point that radiation actually heals their combat injuries. They are most often considered outsiders even by other ghouls. The glowing ones emit radiation, so they can still be dangerous to normal humans even after their death.
Background
“A glowing one is a unique feral ghoul that has become a living conduit of radiation.”— Loading screen
The Capital Wasteland glowing ones can emit a wave of radiation at will from their bodies, which they use to heal themselves and any surrounding ghouls while damaging their enemies. They are the alpha males of the feral ghouls and others seem to follow them, as they are attracted to the lethal doses of radiation the glowing ones emit from their bodies.
In the ghoul settlement of Necropolis in the Core Region, the glowing ones lived in the remains of Vault 12, and there was an animosity between them and the "normal" ghouls led by Set, who inhabited the ruins of the town. After Necropolis was overrun by the super mutants, the glowing ones who left the town lived much more harmoniously with the other ghouls (not to mention normal humans and super mutants).
There appear to be several glowing ones in the nuclear plant in Gecko, working in the reactor area, most notably Hank. If the Chosen One fixes the reactor's radiation leak, the ghouls in the plant (not just the glowing ones), will comment on how the plant feels "chilly".
In the Underworld, the doctor of The Chop Shop seems to be using glowing ones as a method to heal the ghoul population. He has two of them, Meat and Ethyl, locked in a pen next to the clinic.
In Los, the glowing ghouls are among the members of the Church of the Lost, a ghoul cult dedicated to protection of the Secret Vault. Interestingly, they are less affected by radiation than their comrades from the Capital Wasteland and the West Coast's Core Region.
“A glowing one uses its special ability to deliver radiation to its enemies and heal any nearby feral ghouls.”— Fallout 3/Fallout: New Vegas loading screens
The distinctive luminescence that is the trademark of the glowing one can be best attributed to an unusually high amount of radioactive chemicals that build up in the bloodstream and muscle tissue of a typical ghoul. Sometimes, upon the transformation into a feral ghoul, the neurological systems of the body cease filtering these particles from the blood and tissue, instead causing them to build a distinctive bio-luminescence that is a characteristic of the "glowing ones". In daylight they simply appear to be incredibly pale feral ghouls, but in darkness they glow with a vivid yellow-green hue, their opaque skeletons clearly visible as in an X-ray. Approaching a deceased glowing one can cause minor exposure to radiation.
