Channel letters are also known as "internally illuminated letters". This description says it all — each letter is generally lit from the inside with light shinning through the plastic sign face or out the back of the letter (called a halo-lit, or reverse channel letter). Channel letters may be installed directly to the building face (each letter is mounted individually) or on a raceway, a pre-fabricated metal box containing the sign’s electrical components that runs the length of the channel letter sign.