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Electrodeless lamp

From Wikipedia, the free encyclopedia

In contrast with all other electrical lamps that use electrical connections through the lamp envelope to transfer power to the lamp, in electrodeless lamps the power needed to generate light is transferred from the outside of the lamp envelope by means of (electro)magnetic fields. There are two advantages of eliminating electrodes. The first is extended bulb life, because the electrodes are usually the limiting factor in bulb life. The second benefit is the ability to use light-generating substances that would react with metal electrodes in normal lamps.

Two systems are described below—one based on conventional fluorescent lamp phosphors, and a second based on the use of direct-radiating sulfur vapor.

History

in 1705 the English scientist Francis Hauksbee demonstrated that a mercury filled evacuated glass globe could emit light, by static electricity. In 1891, Nikola Tesla demonstrated wireless transfer of power to incandescent lamps, US patent 454622. John Anderson General Electric 2, 3 applied for patents in 1967 and 1968 for electrodeless lamps, with a construction almost similar to elctrodeless lamps that are available on the market in 2006. It would last until 1990 before large scale production of induction lamps for lighting purposes would commence.

Fluorescent induction lamps

Aside from the method of coupling energy into the mercury vapor, these lamps are very similar to conventional fluorescent lamps. Mercury vapor in the discharge vessel is electrically excited to produce short-wave ultraviolet light, which then excites the phosphors to produce visible light. While still relatively unknown to the public, these lamps have been available since 1990. The most common form has the shape of an incandescent light bulb. Unlike an incandescent lamp or conventional fluorescent lamps, there is no electrical connection going inside the glass bulb; the energy is transferred through the glass envelope solely by electromagnetic induction.

In the most common form, a glass tube (B) protrudes bulb-wards from the bottom of the discharge vessel (A). This tube contains an antenna called a power coupler, which consists of a coil wound over tubular ferrite core.

In lower-frequency versions of induction systems, the lamp consists of two long parallel glass tubes, connected by two short tubes that have coils mounted around them.

The antenna coils receive electric power from the electronic ballast (C) that generates a high frequency. The exact frequency varies with lamp design, but popular examples include 13.6 MHz, 2.65 MHz and 250 kHz (in physically large lamps). A special resonant circuit in the ballast produces an initial high voltage on the coil to start a gas discharge; thereafter the voltage is reduced to normal running level.

The system can be seen as a type of transformer, with the power coupler forming the primary coil and the gas discharge arc in the bulb forming the one-turn secondary coil and the load of the transformer. The ballast is connected to mains electricity, and is generally designed to operate on voltages between 100 and 277 VAC at a frequency of 50 or 60 Hz. Most ballasts can also be connected to DC voltage sources like batteries for emergency lighting purposes.

In other conventional gas discharge lamps, the electrodes are the part with the shortest life, limiting the lamp lifespan severely. Since an induction lamp has no electrodes, it can have a very long service life. For induction lamp systems with a separate ballast, the service life can be as long as 100,000 hours, which is 11.4 years continuous operation, or 22.8 years used at night or day only. For induction lamps with integrated ballast, the life is 15,000 to 30,000 hours. Extremely high-quality electronic circuits are needed for the ballast to attain such a long service life. Such expensive lamps have special application areas in situations where replacement costs are high.

Philips introduced their QL induction lighting systems, operating at 2.65 MHz, in 1990 in Europe and in 1992 in the US. Matsushita had induction light systems available in 1992. Intersource Technologies also announced one in 1992, called the E-lamp. Operating at 13.6 MHz, it was to be available on the US market in 1993 but as of July 2005 very few of these lamps have been manufactured.

Since 1994, General Electric has produced its induction lamp Genura with an integrated ballast, operating at 2.65 MHz. In 1996, Osram started selling their Endura induction light system, operating at 250 kHz. It is available in the US as Sylvania Icetron.

A new comer in 2006, AMKO GROUP in Taiwan has introduced their induction lamp SOLARA with a dimmable ballast and up to 400 watts of output. The neat thing about these guys is that they integrated heat dissipation solutions into their products by working with Taiwan's CPU cooling manufacturers. The lamp is produced by their subsidiary company, which is a listed company in Singapore, and they have been producing induction lighting systems for more than seven years. Research and development on induction lighting started ten years ago at a post-doctoral research facility in China. In the past, their products were available only exclusively to contracted distributors and OEM customers. That is why only industry insiders and a few researchers know about them.

Research on electrodeless lamps continues, with variations in operating frequency, lamp shape, the induction coils and other design parameters, such as Mercury free gas fills like Indiumhalogenides. Low public awareness and the relatively high prices have so far kept the use of such lamps highly specialized.

Direct-radiating sulfur lamps