A streetlight is made up of various parts. The pole is constructed of wood, steel, aluminum, polyethylene (I believe), or fiberglass reinforced with polyester resin. (A business that also produces fishing rods makes some of the fiberglass ones!) The poles may be painted, powder-coated, or anodized after being treated with creosote or a copper preservative (if made of wood). The lamp housing is typically made of aluminum. Glass or polycarbonate material is used to make the lens. If it's a high-intensity discharge lamp, the ballast is comprised of steel with either aluminum or copper windings. The lamp is composed of glass (an inner capsule may be made of quartz). Metal support wires, noble gases, mercury, sodium compounds, or other metals may be found within. The capsule (or fluorescent tube) may be phosphor-coated. The lamp's base is made of aluminum or brass and is fitted into a porcelain socket with a brass, bronze, or aluminum inner shell. A circuit board constructed of fiberglass and resin with copper or gold traces is included in an LED light. A solder consisting of tin and silver is used to attach circuit components (or tin and lead). The circuit board feeds an array of light-emitting diodes connected to another circuit board, which is mounted to an aluminum heatsink or the lamp's housing with a thermally conductive paste between the board and the sink. Some LED street lighting has a fan to help cool the bulb and electronics. A photoconductor-controlled switch may be used in either light. When light reaches the photoconductor, it conducts electricity to a heating element, which heats a bimetallic strip that separates electrical connections, causing the lamp to switch off. When it becomes dark, the photoconductor stops conducting, causing the element to cool and the bimetallic strip to flex and close the contacts, therefore turning on the light. Of course, the assembly is powered by copper wires insulated by thermoplastic insulation. Steel, aluminum, or plastic conduit may be used to protect these.