You change a flame so that it cannot be extinguished by normal wind, nor ignite other materials.
The affected flames continue to consume their source (lantern oil, torch, etc). However, if they grow larger than a foot in diameter, the spell becomes stretched too thin and ends early. Otherwise, the flames are unaffected by winds of less than gale force, never flickering in even a stiff wind. They cannot be used to ignite combustible material, such as explosive gas, puddles of oil, or even a scrap of paper. They still can burn flesh, however, and are vulnerable to dousing through water, suffocation, or the elimination of their fuel supply.
Arcane material component: A small sphere of glass.