"Lambent" refers to a group of various different lifeforms on the planet Sera that have been heavily mutated after prolonged contact with Imulsion, a low-viscosity, highly volatile fluid that the humans of Sera regularly utilized as a fuel source. For decades, humanity prospered from the refinement of Imulsion, unaware of the true nature of the substance. It would not be until the final days of the Locust War that Imulsion was discovered to be a parasitic lifeform, capable of infecting and corrupting any and all forms of life that came into contact with it.
Discovery of Infection
Around a century before Emergence Day, the substance known as Imulsion was considered to be more of a scientific curiosity than a practical resource after its discovery, and was essentially useless until Dr. Helen Cooper created the Lightmass Process. The process was capable of refining Imulsion into an efficient energy source. In the early years, scientists had no reason to consider Imulsion as a parasite or a living being at all.
Sometime later, in the early years of the Pendulum Wars, COG officials and scientists discovered poisoned, infected Human Imulsion miners. In order to cure the Lambency for continued use of the fuel, the New Hope Research Facility was opened to attempt to find a cure for Lambency. The miners, now known as Sires, were kept for study as they mutated and became savage. However, due to information leaks, recent attacks by the Sires, and failures to find a cure, New Hope was decommissioned as well as the project, and all sources related were erased. This information, however, carried on about the health risk with Imulsion with Chairmen and COG officials. This would remain secret until a public discovery in 15 A.E. The children of the Sires were taken to Mount Kadar where they became the Locust.
Forcing the Locust to the Surface
Five years before E-Day during the Locust Civil War, the Lambent began driving the Locust Horde into extinction. A desperate Queen Myrrah entered into a pact with COG scientist Adam Fenix: if he could find a solution to the Lambent infections, the Locust Horde would not have to invade the surface. Unfortunately the Pendulum Wars forced Adam to create another weapon to help the COG instead of the Locust Horde, taking up his time to make a countermeasure weapon against the Lambent. By the time the Hammer of Dawn was completed, the Locust Horde was preparing to invade the surface after the Pendulum Wars ended.
The Lambent Wretches
Fourteen years after E-Day, during the Lightmass Offensive, the Delta-One Gears led by Marcus Fenix discovered Lambent Wretches for the first time at the Lethia Imulsion Facility and engaged them while trying to gain access to the Hollows and to deploy the Sonic Resonator. The Lambent Wretches were reported to have been seen before by the COG and had in fact been seen six weeks after Emergence Day during the Destruction of Halvo Bay. Unlike the rest of the Lambent, the Lambent Wretches did not appear to be hostile to the Locust and worked with them on the Tyro Pillar. Their presence there may have just been coincidental, as while they did attack, they didn't attack at the same time as the Locust.
Siege of Nexus
During the Siege of Nexus, Delta-One infiltrated Nexus and discovered that the Locust were already engaged in an urban battle with the Lambent. At the time the COG did not know the full effect of the Lambent infection. With the Horde losing ground to the Lambent, the COG discovered how they were able to make great progress in the Hollows, because the Locust were split losing on their home front. Sgt.Marcus Fenix later discovered a Locust defense plan of the city of Nexus showing that the Lambent were attacking from under the city. During the battle, Augustus Cole killed a Lambent Drone which didn't explode and its Imulsion moved on its own up a cliff to the other Lambent Drones there. Later, the squad used the Hammer of Dawn to detonate the Lambent Brumak to sink Jacinto and flood the Hollows.
Infection of the Surface
After several months after the sinking of Jacinto and the flooding of Hollow, the Lambent infection spread to the surface. By this time, they had developed the capability to appear all over the planet through the Lambent Stalks and deploying various different forms. Although at first believed by COG to only infect Locust, Formers - humans infected by Imulsion - begin to appear in areas such as Mercy. Adam Fenix developed a weapon capable of destroying Imulsion and all heavily infected by it, thus the Lambent and the Locust, but was captured by the Queen's Guard during the First Battle of Azura before he could activate it. When the remnants of the COG and the Gorasni launched an attack on the island, the Lambent attacked as well, battling everyone present. Eventually Adam managed to activate the weapon and a wave of Drudges were sent to try to stop him, but were killed by the weapon before they could succeed. The weapon was successfully activated and destroyed all Imulsion across Sera and everything infected by it, including Adam, the Locust and all Lambent life forms, marking the end of the Locust War and Lambent Pandemic.
The Lambent organism lies within the Imulsion and spreads through Imulsion fumes which acclimated after the Lightmass Process. The organism acts as a parasite and will actually kill its host rather than eject and find another. The parasite does, however, possess its host to spread the infection. The plant life acts as transport and fruiting bodies for other forms of Lambent to spread while the animal life is mobile and seeks to kill and infect other living forms.
The sickness, at least for Humans, is followed in stages. The first stage is contraction, in which by 17 A.E. everyone has. However, the Lambent organism is rather dormant unless exposure is constant. The second stage is a form of Rust Lung, in which Imulsion invades the body and lungs via Imulsion fumes. This is shown by extreme coughing and brownish-red mucous and blood bleeding from the mouth, nose, and eyes. This is contracted mostly by Imulsion miners and people near refineries, and those unlucky in Timgad following the Lightmass Offensive when the Lightmass bomb evaporated much of the Imulsion. The third stage is a fever and intense muscle pain, in which the Imulsion has almost colonized one's cells and it has begun heating the blood in its victims' veins. The fourth and final stage is Lambency in which the veins illuminate the golden colour of Imulsion and burns the skin and cartilage, blackening the skin. Finally the parasite possesses the host and aims to kill and infect other beings.
As the Imulsion takes over and kills it host, it also mutates. After the skin is blackened, the veins are illuminated, and the cartilage burns away, the host begins to mutate limbs and tentacles. Lambent hosts differ in mutation depending on the species, mentality, and possessions. Creatures such as Gunkers have mutated their limbs over the butcher cleavers they once held as Butcher Boomers. Regardless, each mutation is very similar. A mutated host has their eye colours turn into yellow-gold, pulses of Imulsion throughout their bodies, and the skin turned into a jet black carapace. Most forms also sprout tentacles forming from the body itself, especially the Lambent Berserker.
The end of the life cycle, whether it is killed or automatically activates it, the Lambent will explode. The Lambent have a mentality to rush and kill rather than think logically and survive. Their mind set is kill and infect. The explosion is a last resort in which the Imulsion exits the body and spreads in the general area, and at times, the Imulsion will mobilize after the death of its host and move to another. This was shown when one of the Lambent Grenadiers in the Siege of Nexus attempted to board the lift Delta Squad was using, only to be killed by Cole. Cole later saw the Imulsion leave the corpse in an attempt to find a new host.
Below is a list of all known Lambent lifeforms encountered by the COG.