Light and Dark are opposites. That means Light and Dark are super effective against each other. Grass resists it, Ice is immune to it. Also, a Plate for this would be called the Glow Plate. And, the item for boosting Light type moves is the Mystery Spark. The Berry for resisting super effective Light type moves is the pomegranate-looking Quigon Berry. Some candidates for Light Type Pokemon include a light bulb who's part Electric, a Legendary who's an angel, and a glowing grub thing who's part Bug. Pokemon retyped to this include the fireflies of Hoenn, Manaphy, and some others. A Light Type Eeveelution would evolve as such with maximum EV training points and at least 2/5 of the Affection meter filled on Amie.