This week’s question was asked by a friend.

QUESTION: Why was the invention of the light bulb such a big deal?

ANSWER: Thomas Edison’s 1879 invention completely transformed the way we live and work. Imagine how hard it must have been to illuminate our world once the sun went down, using messy candles, torches and oil lamps that tended to suck up the oxygen, soot up the room and start disastrous fires.

By 1900, millions of people around the world were turning on the light bulb and turning off the dark. And amazingly, the light bulb has not changed much in nearly 140 years.

The heart of the light bulb is the tungsten filament. Tungsten is a metal that has an extremely high melting temperature of about 6,800 degrees Fahrenheit. But even tungsten would catch on fire at such high temperatures. Fires need oxygen, so bulb makers take out the air inside the bulb. In other words, there is a vacuum (nothing) inside the bulb.

Those clever bulb makers go one step further. They put a tinge of argon gas in the light bulb. Argon is a big heavy atom. When atoms of tungsten evaporate off the filament, they run into the argon atoms that return the tungsten atoms right back onto the filament. The argon atoms act like barroom bouncers.

Bulbs burn out when too much tungsten has evaporated away in one particular spot on the filament. The filament becomes thinner and weaker in that area. The filament is cold, you turn on the bulb, a heavy surge of current goes through that cold filament, and wham, a flash of light and the bulb is dead. We’ve all seen it.

The one-inch filament in a typical bulb is actually over 22 inches long. It is coiled, and the coil is made into a larger coil. Engineers discovered they could get more light per watt with this double coil method.

Light bulb manufacturing is a marvelous example of compromise engineering − a compromise between bulb life vs. bulb efficiency. You could make a bulb last practically forever. Just make the filament real thick. But the bulb would be dim and consume lots of electricity. Not very efficient. On the other hand, you could make a bulb extremely efficient by making the filament thin. It would burn hot and bright but last just a few hours.

Every bulb package is required to have three items on the label: wattage, life in hours, and light output in lumens. A 25-watt bulb will last about 2,500 hours and a 100-watt bulb will last an average of 1,700 hours. The lower the wattage, the longer the life. That’s because the filament is thicker on the low wattage bulb. But the 100-watt bulb is more efficient, which means you get more light per watt of electricity consumed.

A light bulb in a fire station in Livermore, California, has been burning continuously since 1901. That 60-watt bulb is not very bright and not very efficient, but it illuminates the fire engines at night. It is a hand-blown bulb with a carbon filament that is eight times thicker than a modern light bulb.

Many nations are phasing out the manufacture and sale of the time-honored incandescent bulb in favor the more energy efficient CFL (Compact Fluorescent Lamp) and LED (Light Emitting Diode). Leaders in this movement include several South American countries and the European Union.

Contrary to popular belief, the United States government is not banning incandescent light bulbs. What they are doing is putting rules in place that mandate a greater efficiency. It is difficult for a traditional incandescent bulb to meet those standards, but clever manufacturers have found a way around the rules by coming out with a halogen incandescent bulb.

Halogen will not kill the incandescent bulb, but the LED bulb might do the trick. LED bulbs are getting better by increasing their brightness and matching the color and texture of the beloved incandescent bulb. The cost of operating the LED bulb is extremely low.

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Larry Scheckel is a retired Tomah High School science teacher.


Steve Rundio is editor of the Tomah Journal. Contact him at 608-374-7785.

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