The "Los Alamos's Light" is indeed a reference to the Demon core, which is the name give to a sphere of Plutonium used in experiments after WWII. It was originally meant to be the fissile core of an US atomic bomb, but after Japan surrendered it was sent to Los Alamos (in the state of New Mexico) for scientific testing and study.
The "Light" part refers to the "Blue flash" that was witnessed in both incidents with the core, most likely
Cherenkov radiation due to the massive blasts of radiation that happened as part of these incidents.
Kyle Hill's "
Demon Core - The True Story" is a Excellent video explaining what was the demon-core, and both incidents it was involved in.
Kyle Hill has also a whole playlist of similar videos about nuclear-related incidents, if that is of interest.