An alternative to LED lamps

Print edition : August 02, 2019

Cathodoluminescent lamp: (1) cathode modulator unit, (2) cathode, (3) modulator, (4) emitted electrons, (5) phosphor, (6) aluminum mirror serving as anode, (7) anode output, (8) glass vacuum tube. Photo: Evgenii Sheshin et al/Journal of Vacuum Science and Technology

Researchers from the Moscow Institute of Physics and Technology (MIPT) and the Lebedev Physical Institute of the Russian Academy of Sciences have designed and tested a prototype cathodoluminescent lamp for general lighting that could unleash a lamp revolution. The new lamp, which relies on the phenomenon of field emission, is more reliable, durable and luminous than its analogues available worldwide. The development has been reported in the “Journal of Vacuum Science & Technology B”.

While LED lamps have become commonplace, they are not the only clean and power-saving alternative to incandescent lamps. Cathodoluminescent lamps rely on the same principle as old TVs, using cathode-ray tubes. A negatively charged electrode, or cathode, at one end of a vacuum tube serves as an electron gun. A potential difference of up to 10 kilovolts accelerates the emitted electrons towards a flat positively charged phosphor-coated electrode—the anode—at the opposite end of the tube. This electron bombardment results in light. Such lamps can emit light at any wavelength, from the red to ultraviolet (UV), depending on which fluorescent material is used.

Cathodoluminescent UV light bulbs contain no mercury and are generally cleaner in service and upon disposal.“Cathodoluminescent lamps could be used in medicine, like for operating room decontamination, UV irradiation of throat and tonsils, and dental filling curing,” commented Mikhail Danilkin of the Lebedev Physical Institute. Another important advantage of the new lamp over LEDs and fluorescent bulbs is that it does not rely on so-called critical raw materials, which include gallium, indium and some rare-earth elements, whose supply is limited and irreplaceable in health, defence, aerospace and other key industries.

However, designing an efficient, long-lasting and technologically advanced cathode that could be mass-produced and sold at an affordable price has proved challenging. While there are ongoing efforts in Japan and the U.S., this Russian study marks the first successful attempt at this. “Our field emission cathode is made of ordinary carbon,” said Professor Evgenii Sheshin of the MIPT, who led the research team. “But this carbon is not used merely as a chemical but rather as a structure. We found a way to fashion a structure from carbon fibres that is resistant to ion bombardment, outputs a high emission current and is affordable in production.” The MIPT research group has also developed a compact power source for its cathodoluminescent lamp. The source is fitted around the glass light bulb with almost no effect on its size. The luminous power is up to 250 lumens, about the output of a 25-watt incandescent lamp, but the power consumption is only 5.5 watts. The technical characteristics and prototype test data reported in the paper suggest that if mass-produced, these new bulbs could compete with LED lamps.

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