Whitelight was developed by Dr. Archer and her team as a cure for the Blacklight virus made by Gentek. However, Alex Mercer ordered Archer, who was one of his Evolved, to taint it with his blood before it was deployed. The tainted Whitelight infected those exposed with Blacklight, rather than curing them, turning them into Evolved, Infected, or simply killing them.

Even after the tainting of the cure was discovered, it was still kept due to its potential as a bioweapon though Blackwatch canceled the large scale deployment of the "cure". James Heller can find Whitelight in all three of NYZ's zones after uncovering its effects, and can use it to turn any human target into an Infected, but never an Evolved.

Trivia

• In “Fall from Grace” those exposed to Whitelight turn into Evolved, and dialogue indicates that this is the normal effect of exposure. This suggests that Mercer genuinely was attempting to convert humanity into sentient Evolved as opposed to mindless zombies.
• Before the mission "Fall from Grace", the barrels will emit white fumes when leaking, rather than the red color shown after. It has no gameplay effect in this state; possibly it only cures those in early stages of infection, or serves as a vaccination rather than a cure, or it’s supposed beneficial effects were made up by Archer and other Evolved within the project.
• While in free roam, Whitelight cannot create Evolved but can create Walkers, or may simply kill victims rather than turning them into infected.
• When you grab a military or Blackwatch member in progress of becoming a Walker, the virus will not work and they will become normal but without any weapons. When they spot you, they will not shoot and act like scared citizens.
• In the Sub-mission where you would incinerate the last remaining barrels, the Evolved guarding it is in the left side of your view.
  • When you are holding a scientist or Blackwatch trooper while being exposed to leaked Whitelight barrel, the scientist or Blackwatch trooper would break out of your grasp and will turn to Evolved.
• In the Excessive Force Pack DLC, the Viral Infector grenade launcher has the same effects as infected Whitelight.
• Whitelight containers that can be picked up are always blue and red. Another container containing Whitelight is bigger and silver which cannot be picked up and will take more damage before Whitelight will leak out of it.
• When Whitelight was said to be highly mutable, it shows a person to what it was not going to be, but if it did Whitelight would cure many of the civilians.
• Over all Prototype sites; one says that Pariah is Whitelight, which could mean that Whitelight is a refined version of the Redlight virus.

Gallery

James Heller infecting civilians.