In variations of this particular reality, the Green Lanterns drew energy from a central power battery on the planet Oa and used willpower to focus this energy through individual batteries and power rings. The green light energy required the user be free of the emotional fear, which itself could be focused as the color yellow from the same source of primordial energy. To establish checks and balances, the Green Lantern energy was useless against the color yellow for that reason.
In most versions of that multiverse, the Green Lantern Corps was divided into space sectors, with each assigned a Green Lantern ring bearer as protector. The planet Earth, important to the Guardians protection, had many different champions who had Green Lantern power rings. (TOS - The Spectrum War comics: "Issue 1", "Issue 2")