Stormlight is the fuel for the magic system on Roshar, known as Investiture. The process by which Stomlight is gathered is infusion. During a highstorm, Stormlight is generated. This Stormlight provides energy that can be infused into either gems or people.
Infusion in GemsEdit
Gem's on Roshar are generally encased in glass and then called spheres. These spheres glow when they are infused with Stormlight, and are considered 'dun' once all the Stormlight has drained out of them.
Spheres serve numerous purposes on Roshar as they are used primarily as light sources given that they glow when infused. They are also used as currency; dun spheres are worth the same as infused spheres, though are treated warily as they can be counterfeited. Additionally, spheres power such things as Shardplate and fabrials. No sphere perfectly contains Stormlight, so over time they gradually go dun, but go faster when being used to power Plate, especially when that Plate is damaged.
To infuse a sphere, it only needs to be left exposed during a highstorm and it is then fully charged with Stormlight.
Infusion in PeopleEdit
Very few people on Roshar can infuse Stormlight. The most common way is by forming a Nahel bond with a spren, therefore taking a step to becoming one of the Knights Radiant. Alternatively, possessing a Honorblade allows an individual to infuse Stormlight.
People who can infuse Stormlight can either infuse it directly from a highstorm, or from an infused sphere.
When a person is infusing Stormlight quickly, wisps of Stormlight can be visibly seen going from the source of their Stormlight.