Electric lamp and discharge devices: systems – Pulsating or a.c. supply – Induction-type discharge device load
Reexamination Certificate
1997-10-14
2001-01-16
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
Induction-type discharge device load
C315S344000, C313S490000
Reexamination Certificate
active
06175197
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to low pressure, electrodeless discharge lamps and, more particularly, to electrodeless discharge lamps wherein the temperature of an amalgam is controlled by providing a thermal connection between the transformer core and the amalgam.
BACKGROUND OF THE INVENTION
Electrodeless fluorescent lamps are disclosed in U.S. Pat. No. 3,500,118 issued Mar. 10, 1970 to Anderson; U.S. Pat. No. 3,987,334 issued Oct. 19, 1976 to Anderson; and Anderson,
Illuminating Engineering,
April 1969, pages 236-244. An electrodeless, inductively-coupled lamp, as disclosed in these references, includes a low pressure mercury/buffer gas discharge in a discharge tube which forms a continuous, closed electrical path. The path of the discharge tube goes through the center of one or more toroidal ferrite cores such that the discharge tube becomes the secondary of a transformer. Power is coupled to the discharge by applying a sinusoidal voltage to a few turns of wire wound around the toroidal core that encircles the discharge tube. A current through the primary winding creates a time-varying magnetic flux which induces along the discharge tube a voltage that maintains the discharge. The inner surface of the discharge tube is coated with a phosphor which emits visible light when irradiated by photons emitted by the excited mercury atoms. The lamp parameters described by Anderson produce a lamp which has a high core loss and is therefore extremely inefficient. In addition, the Anderson lamp is impractically heavy because of the ferrite material used in the transformer core.
An electrodeless lamp assembly having high efficiency is disclosed in U.S. patent application Ser. No. 08/624,043, filed Mar. 27, 1996 (now U.S. Pat. No. 5,834,905). The disclosed lamp assembly comprises an electrodeless lamp including a closed-loop, tubular lamp envelope enclosing mercury vapor and a buffer gas at a pressure less than about 0.5 torr, a transformer core disposed around the lamp envelope, an input winding disposed on the transformer core and a radio frequency power source coupled to the input winding. The radio frequency power source typically has a frequency in a range of about 100 kHz to about 400 kHz. The radio frequency source supplies sufficient radio frequency energy to the mercury vapor and the buffer gas to produce in the lamp envelope a discharge having a discharge current equal to or greater than about 2 amperes. The disclosed lamp assembly achieves relatively high lumen output, high efficacy and high axial lumen density simultaneously, thus making it an attractive alternative to conventional VHO fluorescent lamps and high intensity, high pressure discharge lamps.
Another type of electrodeless lamp is disclosed in U.S. Pat. No. 4,298,828 issued Nov. 3, 1981 to Justice et al. A globe-shaped lamp, wherein the discharge path is irregular in shape and is confined to an approximately spherical lamp envelope, is disclosed. A transformer core is located within the lamp envelope.
Yet another type of electrodeless lamp is disclosed in U.S. Pat. No. 5,239,238 issued Aug. 24, 1993 to Bergervoet et al. A transformer core is positioned in a reentrant cavity of a generally globe-shaped electrodeless lamp envelope.
The high wall temperatures of the lamp envelopes in the aboved-scribed lamps necessitates the use of mercury amalgams to ensure near optimum mercury vapor pressure during typical operation. Amalgams also have the advantage of substantially increasing the useful temperature range of the lamps. However, under some conditions, the amalgam temperature can drop below the optimum temperature range. In this case, output lumens and efficacy drop, and lamp color can shift due to the drop in mercury vapor pressure. These undesirable changes can occur in globe-shaped lamps, which do not have an integral ballast to provide amalgam heating, and also in tubular lamps. Temperatures below optimum can occur when lamp power is reduced during dimming and in low ambient temperatures, and also when the lamp is operated outside a fixture.
In tubular electrodeless lamps, the most practical location for the amalgam is in the exhaust or dummy tubulation. With lamps of typical loading operating in an indoor enclosed fixture, the amalgam temperature reaches about 85° C. to 95° C., well within the temperature range which gives lumens greater than 90% of peak. However for outdoor use, it is desirable to maintain high lumen output down to minus 20° C. or lower. Under these conditions, lumen output can drop far below peak. Also, in open air at normal room temperature of 25° C., the amalgam drops to below the temperature range that gives a lumen output greater than 90% of peak for common amalgam systems based on bismuth, tin and lead or bismuth and indium.
Accordingly, it is desirable to provide electrodeless lamp configurations and methods of operating electrodeless lamps which provide high lumen output over a wide range of operating temperatures.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, an electric lamp assembly is provided. The lamp assembly comprises an electrodeless lamp including an electrodeless lamp envelope, a transformer core, disposed in proximity to the lamp envelope and an input winding disposed on the transformer core. The electrodeless lamp envelope encloses a fill material for supporting a low pressure discharge. The electrodeless lamp further includes an amalgam located within the lamp envelope. The input winding receives radio frequency energy from a radio frequency source. The radio frequency energy produces a low pressure discharge in the lamp envelope. The lamp envelope further comprises a thermal connection between the transformer core and the amalgam, wherein the amalgam is heated by the transformer core during operation.
In a preferred embodiment, the lamp envelope comprises a closed-loop, tubular lamp envelope, and the transformer core is disposed around the lamp envelope. The amalgam may be located in an exhaust tubulation of the lamp envelope, and the thermal connection may comprise a thermal bridge between the transformer core and the exhaust tubulation. The thermal bridge may comprise a thermally-conductive metal or a thermally-conductive cement in thermal contact with the transformer core and the exhaust tubulation. The lamp assembly may further include a core retainer disposed around the transformer core. In this configuration, the thermal connection between the transformer core and the amalgam may comprise a thermal connection between the core retainer and the exhaust tubulation. In another embodiment, the amalgam is located in close proximity to the transformer core, and thermal energy is transferred from the transformer core to the amalgam through the lamp envelope.
According to another aspect of the invention, an electrodeless lamp assembly is provided. The lamp assembly comprises an electrodeless lamp including a closed-loop, tubular lamp envelope, a transformer core disposed around the lamp envelope, an input winding disposed on the transformer core and a radio frequency power source coupled to the input winding. The lamp envelope encloses mercury vapor and a buffer gas. The electrodeless lamp further includes an amalgam located within the lamp envelope. The radio frequency power source supplies sufficient radio frequency energy to the electrodeless lamp to produce a low pressure discharge in the lamp envelope. The lamp assembly further comprises a thermal connection between the transformer core and the amalgam, wherein the amalgam is heated by the transformer core during operation.
According to a further aspect of the invention, a method for operating an electric lamp assembly is provided. The lamp assembly comprises an electrodeless lamp including an electrodeless lamp envelope enclosing a fill material for supporting a low pressure discharge, a transformer core disposed in proximity to the lamp envelope and an input winding disposed on the transformer core. The electrodeless lamp further includes an amalgam located within the lamp env
Bessone Carlo S.
Osram Sylvania Inc.
Vu David
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