. blackout A specially formulated paint or coating for use on electric signs to block light emission where needed, for example between letters in a neon sign. It adheres well to glass... signs to block light emission where needed, for example between letters in a neon sign. It adheres well to glass, and resists weather, heat and electrical discharge. (Also called... of glass tubing used in neon signs that is coated on the inside surface with a phosphorus compound. The color a coated tube will produce depends on the specific compound used. cold...