9781422284902

There were lights that used halogen , xenon , LED, or even la- sers. “I had no idea there were so many options,” he admitted. “And,” Emmett continued, “I guess I really don’t see the difference.” Uncle Gus pointed to one headlamp. “This is a halogen headlamp. According to this, they are the most common headlights in use today.” Emmett thought a moment

current a flow of electrons incandescent creating light through heat halogen nonmetallic elements on the periodic table within the same group periodic table chart of the elements show- ing patterns of properties vendor a salesperson or a company that sells products to industry xenon a gaseous element that can be used in lighting Words to Understand

and then said, “I remember learning about halogen in sci- ence class. Isn’t that a group of elements on the periodic table?They make headlights out of that stuff?” “Yes,” Uncle Gus nodded. “The halogens are a group of elements on the periodic table . They are fluorine, chlorine, bromine, iodine, and astatine. These elements are special because they can form compounds with just about any metal on the periodic table. The word halogen means ‘self- forming.’ These elements form salts.” “That’s right. Like sodium chloride,” said Emmett. “Exactly. Sodium chloride, or table salt, is formed when chlorine, a halide, combines with sodium, a metal.” “So why are halogens used in light bulbs?” wondered Emmett. Uncle Gus picked up one of the sample light bulbs from the display. “This is an incandescent light bulb. They actually don’t make them anymore. But if you look inside, you’ll see that there Uncle Gus smiled and continued, “An electric current heats the tungsten filament and it glows, giving off light. But this tungsten filament by itself like this won’t last very long. It might last 750 or 1,000 hours of normal use, and gives off a tremendous amount of heat. That is really just wast- ing energy. As it heats up, the tungsten evaporates. Eventually, the filament breaks.” Picking up a halogen headlight, Uncle Gus went on, “This light bulb also has a tungsten fila- ment. But inside the bulb is one of the halogen gases, either fluorine or chlorine.” Emmett looked at another set of bulbs. “These are even brighter. What are they made of ?” is a thin filament or wire. This is made out of tungsten, a kind of metal.” Emmett interrupted, “And another element on the periodic table!”

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