Red Lums are one of the four types of Lum which make up the universe. Red Lums contain vital energy and can prolong one's life. In Rayman 2, Robo-Pirates have a certain affinity for them, and Rayman can take the Red Lums which the pirates have collected by defeating them.
Red Lums can become Black Lums when they are frightened, and making them laugh will change them back. Perhaps, these Lums are special in some way. These lums seem to react with emotions, this is not explained however. Red lums could, in fact, be organic. They have appeared in all platforming Rayman games, with the exception of Rayman 1, where they are round balls (it could be, however, assumed that these round balls still are Red Lums as both fulfill the same purpose of healing Rayman).
Red Lums have a close resemblance to Leaf, from The Legend of Zelda: Phantom Hourglass. Due to the Red Lums' color, they share that same color trait as Leaf, though their wings are clear, while Leaf's wings are red.