Electric blue is a color whose definition varies but is often considered close to cyan, and which is a representation of the color of lightning, an electric spark, and the color of ionized argon gas; it was originally named after the ionized air glow produced during electrical discharges, though its meaning has broadened to include shades of blue that are metaphorically "electric" by virtue of being "intense" or particularly "vibrant". Electric arcs can cause a variety of color emissions depending on the gases involved, but blue and purple are typical colors produced in the troposphere where oxygen and nitrogen dominate.