Radiant energy is a type of energy associated with the Divination skill. It can be collected from Radiant wisps, located on Dragontooth Island, at level 85 of Divination. Each harvest of a Radiant wisp yields 20 Divination experience if an Enriched radiant memory is harvested, and 10 Divination experience otherwise. Radiant memories can be converted to Radiant energy for 1 experience each, with the exact amount of energy per memory depending on your Divination level.
One radiant memory and 5 radiant energy can be converted for 47.5 experience, while one enriched radiant memory and 10 energy can be converted for 95 experience.