Electrodeless lamp

In contrast with typical 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 three advantages of eliminating electrodes:

• Extended lamp life, because the electrodes are usually the limiting factor in lamp life.
• The ability to use high efficiency light-generating substances that would react with metal electrodes in normal lamps.
• Improved collection efficiency because the source can be made very small without shortening life - a problem in electroded lamps

Two systems are described below—one, plasma lamps, based on on the use of radio waves energizing a bulb filled with sulfur or metal halides the other, fluorescent induction lamps, based conventional fluorescent lamp phosphors.

History

Nikola Tesla demonstrated, wired and wireless transfer of power to electrodeless fluorescent and incandescent lamps in his lectures and articles in the 1890's, and subsequently patented a system of light and power distribution on those principles. In the lecture before the AIEE, May 20, 1891, titled Experiments with Alternating Currents of Very High Frequency and Their Application to Methods of Artificial Illumination ^[1] and US patent 454622, among many other references in the technical and popular press are found countless records for Tesla's priority in this field. A suit filed by Tesla against J. J. Thomson for priority on the patent was subsequently granted in Tesla's favor. The transcripts of the case languish currently in archives, awaiting processing, and eventual publishing. Noting the diagrams in Tesla's lectures and patents, a striking similarity of construction to electrodeless lamps that are available on the market currently is readily apparent. Further, a statement in 1929 by Tesla, published in The World :

Surely, my system is more important than the incandescent lamp, which is but one of the known electric illuminating devices and admittedly not the best. Although greatly improved through chemical and metallurgical advances and skill of artisans it is still inefficient, and the glaring filament emits hurtful rays responsible for millions of bald heads and spoiled eyes. In my opinion, it will soon be superseded by the electrodeless vacuum tube which I brought out thirty-eight years ago, a lamp much more economical and yielding a light of indescribable beauty and softness.

In 1967 and 1968, John Anderson of General Electric ^{[2] [3]} applied for patents for electrodeless lamps. 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.

In 1990, Michael Ury, Charles Wood and colleagues, formulated the concept of the sulphur lamp. With support from the United States Department of Energy, it was further developed in 1994 by Fusion Lighting of Rockville, Maryland, a spinoff of the Fusion UV division of Fusion Systems Corporation. Its origins are in microwave discharge light sources used for ultraviolet curing in the semiconductor and printing industries.

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 the Sylvania Icetron.

In 2006, AMKO SOLARA in Taiwan branded an OEM product with SOLARA. Their induction lamps have dimmable ballasts and up to 400 watts of output. Their induction lighting products operate at 250 kHz.

From 1995, the former distributors of Fusion, Jenton / Jenact, expanded on the fact that energised UV-emitting plasmas act as lossy conductors to create a number of patents with respect to electrodeless UV lamps in the sterilisation / germicidal field.

Around 2000 a system was developed that concentrated radio frequency waves into a solid dielectric waveguide made of ceramic which energized a light emitting plasma in a bulb positioned inside. This system, for the first time, permitted an extremely bright and compact electrodeless lamps. The invention has been a matter of dispute. Claimed by Frederick Espiau (then of Luxim now of Topanga Technologies), Chandrashekhar Joshi and Yian Chang, these claims were disputed by Ceravision Limited ^[4]. Recently a number of the core patents were assigned to Ceravision ^{[5] [6]}.

In 2006 Luxim introduced a projector lamp product trade-named LIFI. The company further extended the technology with light source products in instrument, entertainment, street, area and architectural lighting applications among others throughout 2007 and 2008.

In 2009 Ceravision Limited introduced the first High Efficiency Plasma (HEP) lamp under the trade name AlvaraThis lamp replaces the opaque ceramic waveguide used in earlier lamps with an optically clear quartz waveguide giving greatly increased efficiency. In previous lamps, though the burner, or bulb, was very efficient, the opaque ceramic waveguide severely obstructed the collection of light. A quartz waveguide allows all of the light from the plasma to be collected.

Plasma lamps

Plasma lamps are a family of light sources that generate light by exciting a plasma inside a closed transparent burner or bulb using radio frequency (RF) power. Typically, such lamps use a noble gas or a mixture of these gases and additional materials such as metal halides, sodium, mercury or sulfur. A waveguide is used to constrain and focus the electrical field into the plasma. In operation the gas is ionized and free electrons, accelerated by the electrical field collide with gas and metal atoms. Some electrons circling around the gas and metal atoms are excited by these collisions, bringing them to a higher energy state. When the electron falls back to its original state, it emits a photon, resulting in visible light or ultraviolet radiation depending on the fill materials.

The first plasma lamp was an ultraviolet curing lamp with a bulb filled with argon and mercury vapor developed by Fusion UV. That lamp led Fusion Systems to the development of the sulfur lamp, a bulb filled with argon and sulfur which is bombarded with microwaves through a hollow waveguide. Fusion Lighting went bankrupt, but other manufacturers are having increasing commercial success with the technology.

In the past, the reliability of the technology was limited by the magnetron used to generate the microwaves. Solid state RF generation can be used and gives long lives. However, using solid state chips to generate RF is approximately fifty times more expensive currently than using a magnetron and so only appropriate for high value lighting niches. It has recently been shown by Dipolar [1] of Sweden to be possible to greatly extend the life of magnetrons to over 40,000 hours ^[7] making low cost plasma lamps possible. Plasma lamps are currently produced by Ceravision and Luxim and in development by Topanga Technologies

Ceravision has introduced a combined lamp and luminaire under the trade name Alvara for use in high bay and street lighting applications. It uses an optically clear quartz waveguide with an integral burner allowing all the light from the plasma to be collected. The small source also allows the luminaire to utilize more than 90% of the available light compared with 55% for typical HID fittings. Ceravision claims the highest Luminaire Efficacy Rating (LER) ^[8]of any light fitting on the market and to have created the first High Efficiency Plasma (HEP) lamp. Ceravision uses a magnetron to generate the required RF power and claim a life of 20,000 hours.

Luxim's LIFI, or light fidelity lamp, claims 120 lumens per RF watt (ie before taking into account electrical losses) .^[9] The lamp has been used in Robe lighting's ROBIN 300 Plasma Spot moving headlight.^[10] It was also used in a line of, now discontinued, Panasonic rear projection TV's.^[11].

Fluorescent induction lamps

A Philips QL induction lighting system, where A) Discharge vessel, B) Tube with power coupler and C) Electronic ballast.

A LitePak Systems Kumho induction lighting system, 110v-240v AC 100 watts

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 a 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 lamp can also be a single ring-shaped tube.

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. 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 lamps are typically used in commercial or industrial applications. Typically operations and maintenance costs are significantly lower with induction lighting systems due to their industry average 100,000 hour life cycle and ten year warranty.

References

1. ^ "Experiments with Alternate Currents of Very High Frequency and Their Application to Methods of Artificial Illumination," AIEE, Columbia College, N.Y., May 20, 1891
2. ^ Electrodeless gaseous electric discharge devices utilizing ferrite cores
3. ^ High frequency electrodeless fluorescent lamp assembly
4. ^ Ceravision Steps up Legal Action Against Luxim to Recover IP
5. ^ MICROWAVE ENERGIZED PLASMA LAMP WITH SOLID DIELECTRIC WAVEGUIDE
6. ^ PLASMA LAMP WITH DIELECTRIC WAVEGUIDE
7. ^ http://www.prnewswire.com/news-releases/ceravision--dipolar-form-global-alliance-to-take-ultra-efficient-lighting-technology-to-market-61908532.html
8. ^ http://www.nema.org/stds/LE5B.cfm Procedure for Determining Luminaire Efficacy Ratings for High-Intensity Discharge (HID) Industrial Luminaires
9. ^ "A lightbulb powered by radio waves". cnet. 2007-08-23. http://www.news.com/8301-10784_3-9764945-7.html. 
10. ^ "Robe Launches ROBIN 300 Plasma Spot". Robe lighting. 2009-04-27. http://www.robe.cz/default.aspx?contentid=793fbd23-d794-4cee-a756-6847b822a02c&lang=9d2d0548-2d4a-46fb-8ab2-3e356457ee73&newsid=157dc2d2-7929-4aeb-ac16-779b8a3aec52&page=1. 
11. ^ "The gift of LIFI: Panasonic projection TVs don't burn out". cnet. 2007-01-09. http://news.cnet.com/8301-17938_105-9675567-1.html. 

See also

• List of light sources
• Induction cooker

External links

• Examples of Electrodeless lamps
• Radio frequency lamps overview
• Architectural Lighting magazine article on induction lighting

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