The Forces of Light refers to a gathering of good-alligned warriors in the game Mortal Kombat: Armageddon. They are the opposing army that clashes with the Forces of Darkness in the Battle of Armageddon.
In the intro sequence of the game, and in the final moments of its Konquest mode, two armies, the Forces of Light and the Forces of Darkness, do battle in the southlands of Edenia. They are interrupted by the rising of the Pyramid of Argus, and atop it is Blaze. The two armies now race to the top, each individual hoping to defeat the fire-elemental and absorb his power. Each character's ending in the game is what happens if they were the one to defeat Blaze and take the prize for themself.
As revealed in the biography for Johnny Cage, he is the one who started gathering the Forces of Light, due to Liu Kang's death and Raiden's corruption (although the latter does still join the gathering). In the biography of Kenshi, it states that he desired to lead them, but it is not known if he actually did so and in the Unchained ending of Kitana, she was originally told by Blaze that she must unite the forces of good but apparently, she was helping Liu Kang's spirit after this. Liu Kang's corpse joins neither side, but only seeks the destruction of his murderer and arch-nemesis, Shang Tsung.
All members perished in the first timeline. Raiden was the last one to fall, but just before he did, he sent a warning back in time to his past self, creating a second timeline.