Okay, technically, it's not a light bulb, but it is really, really small.  IBM researchers have made a light source out of a single carbon nanotube.  The nanotube is a semiconductor transistor 1.4 nanometers in diameter, or about 50,000 times thinner than a human hair.  To get an idea of how small that is, keep in mind that an atom is approximately 0.25 nanometer across.

Nanotubes are a form of "fullerene" or "buckyball," a unique molecule comprised of carbon atoms linked in hexagonal rings.  Fullerenes take their name and nickname from Buckminster Fuller, the visionary designer and futurist who devised the geodesic dome, which fullerenes resemble on a molecular scale.  Nanotubes, which were discovered by a Japanese scientist in 1991, are tube-shaped fullerenes.  They display some unique properties.  Nanotube fibers are the strongest fibers known, 10 to 100 times stronger than steel relative to their weight.  The tubes are made of rolled-up sheets of linked carbon atoms and they can be either metals or semiconductors, depending on how they are rolled.

The IBM team created a field-effect transistor out of a single carbon nanotube.  By placing electrodes at both ends of the tube and simultaneously injecting electrons from one end and holes (the absence of electrons) from the other, they caused the electrons and holes to annihilate one another, giving off energy in the process.  In this experiment the energy was given off in the form of infrared light (the same frequency used in optical telecommunications devices), but the researchers say it should be possible to vary the frequency by changing the diameter of the tubes.

The potential applications of this remarkable technology include computer chips that operate entirely with light, incredibly small telecommunications equipment, and, no doubt, a range of devices that we cannot even imagine today.

"IBM Scientists Create World's Smallest Solid-State Light Emitter," IBM Research News (May 1, 2003).  IBM's press release on the publication of a paper describing this achievement.

J. A. Misewich, et al., "Electrically Induced Optical Emission from a Carbon Nanotube FET," Science (May 2, 2003). The technical paper describing the experiment. [Free access to full text restricted to AAAS members and institutions with site licenses to Science; copies of individual articles may also be purchased online.]

Mitch Jacoby, "Nanosized Lite Brite," Chemical & Engineering News (May 5, 2003).  "Lite Brite," in case you've forgotten, is a toy that features various-colored lucite rods that can be inserted in an illuminated peg board to make pictures. 

electricnews.net, "IBM Builds the World's Smallest Torch," The Register (May 5, 2003).  A "torch" is the British term for what we Americans call a flashlight.

"Nanotube shines telecom light," Technology Research News (May 7/14, 2003).  A brief news article.

"IBM Creates Smallest Solid State Light Emitter, Photonics.com (May 9, 2003).  Article drawing heavily on the IBM press release cited above.

"IBM Creates World's Smallest Solid-State Light-Emitter ," NanotechnologyPlanet.com (May 2, 2003).  Ditto.

Additional resources on nanotubes and related technologies:
       ScienceFriday (May 23, 2003) -- National Public Radio talk show on "Future Electronics."
       Peter Harris's carbon nanotube page.  An excellent technical and non-technical.resource.
       NASA Johnson Space Center Carbon Nanotube Project homepage.
       Fullerene Science Module, by two chemistry professors at Washington University in St. Louis.
       Kim Allen's Fullerene Page.
       SUNY Stony Brook Buckyball Homepage. 
       Carbon Nanotube Research Laboratory, SungKyunKwan University (Korea).
       Carbon Nanotubes (from the Physics Department at Penn State University).

An earlier Tech Tidbit of mine devoted to nanotechnology (April 23, 2001).