The Glow, or Ancient Order, as referred to by some Brothers, was a research facility, ran by WestTech, a company which conducted several research projects for the US Government. They are the ones responsible for T-51b Power Armor and Forced Evolutionary Virus (I).
Apparently, they also performed tests with plasma and laser weapons, as we can find a Winchester P94 Plasma Rifle on level 5, 'Secure Testing Labs'.
The facility is maintained by ZAX, an artificial intelligence, who knows everything as far as his sensors reach. Due to the damage done by falling nukes (as Kharn stated, a bunker-buster mini-nuke), levels 1-3 have been deemed inoperable, as ZAXs sensors and control there is destroyed, with 4-6 experiencing heavy damage, but retaining minimal operational capability.
On one of the Holodiscs found on level 5 (Alpha AFAIR), there is a full record of FEV Batch tests performed here, on subjects ranging from flatforms to Chimpanzees. As the tests on primates were concluded, the US Government sent in a military team, under the command of col. Spindel (Roger Maxson, captain, was part of that group) to secure the research data and safeguard it's transport to Mariposa Military Base, where tests were to be conducted on 'voluntary' human subjects (which in reality were soldiers imprisoned for desertion or similiar deeds).
As Maxson discovered the truth of what was going on in the facility, and Spindel commited suicide, he tried to make Leon Von Felden, chief of WestTech Research Facility, tell him what the project really was. Unfortunately it was 23rd October 2077, and nukes fell, one hitting and destroying WestTech, along with Leon Von Felden.
Convinced that Chinese would surely destroy Mariposa next, after a few days, he and his soldiers left for Lost Hills Security Bunker. It was during this event, dubbed the Exodus, that a small faction of the Brtotherhood, led by sergeant Dennis Allen, stole supplies and weapons from their brothers-in-arms and left for the Glow, to seek technology stored within. Despite wearing Power Armors, they were killed off by WestTechs Research Facility automated defence systems. Before dying, Allen recorded a short transcript of their expedition, for anyone coming there to find.
The story picks up much later, when the Vault Dweller arrives here, looking for the Holodisc, in order to complete the quest required to join the Brotherhood.
At the time of 2242, NCR has a state called Dayglow, which supposedly also covers the Glow, where a scavenging community of ghouls (even a Supermutant is said to live there) exists, trading technology for supplies.
