As inventors in the early 1900s vied to devise the best incandescent lightbulb, tungsten won out over carbon for making filaments. Today, however, there’s a form of carbon that was unknown back then—the carbon nanotube.
New experiments on fibers synthesized from those minuscule cylinders suggest that carbon may be the filament champ after all, says Bingqing Wei of Louisiana State University in Baton Rouge. Not all scientists are convinced, however.
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Individual carbon nanotubes, each only a few atoms in diameter, exhibit remarkable traits. For instance, they’re superstrong and can behave like transistors (SN: 2/7/04, p. 87: Virtual Nanotech). Recently, scientists have begun making hair-thick fibers from the nanoscale tubes (see “Nice Threads,” in this week’s issue: Nice Threads).
In a series of experiments, Wei and his colleagues from Tsinghua University in Beijing strung a nanotube fiber between two electrodes, sealed the assembly inside an airless glass bulb, and measured light output at various voltages.
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Two research teams had previously reported incandescent light from nanotube-fiber filaments, but not in actual lightbulbs.
In the June 14 Applied Physics Letters, Wei and his coworkers offer evidence that, at voltages above about 10 volts, a nanotube-filament bulb emits more light per volt than does a tungsten-filament bulb. This brightness indicates that nanotube bulbs use power more efficiently than do their tungsten cousins, the scientists say.
Other scientists say the claim is a stretch. Because Wei’s team didn’t measure both voltage and current in the filaments, any claims about power consumption are guesswork, says lighting researcher Francis M. Rubinstein of Lawrence Berkeley (Calif.) Laboratory. Wei and his colleagues “don’t have the basis for the claim they make,” agrees Ray H. Baughman of the University of Texas at Dallas in Richardson. Wei concedes that current measurements could strengthen his team’s claim.
The new report indicates that an electronic process akin to what occurs in light-emitting diodes, not just the heating that makes a tungsten filament glow, contributes to a nanobulb’s brightness. Recent studies have found a similar electronic process in individual nanotubes, notes Howard K. Schmidt of Rice University in Houston. For the process to show up in such large-scale components as bulb filaments is “really pretty interesting stuff” that deserves further study, he says.