A neon sign is a lighting display made of glass tubes that have been filled with a gas. They are bent into the shape of letters or decorative designs. High-voltage electrical currents are passed through the gas to emit light. They can produce a spectrum of over 50 brilliant colors. Neon signs can be as simple as a small advertising sign hung in a window or wall, or as complex as a multi-story facade on a high rise building incorporating many different types of materials into the fabrication of the neon signs. Manufacturing neon signs are considered an art with a mechanical process. Each sign is unique with few exceptions and must be designed to fit the available space for the desired display.