Abstract:
A gas discharge lamp includes an outer glass tube having a phosphor coating on an inner surface of the outer glass. An inner glass tube is positioned inside the outer glass tube and formed of glass that is transparent to UV light. The inner glass tube contains a plasma-forming gas within an inner volume of the glass tube. A high frequency ballast is integral to the outer glass tube and configured to provide a high frequency AC waveform for driving electrodes configured for energizing the plasma-forming gas within the inner glass tube to form plasma paths therein.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims priority under 37 C.F.R. § 119 to provisional application Ser. No. 60/460,756 filed on Apr. 4, 2003, entitled “High Efficiency Gas Discharge Lamps,” which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND  
       [0002]     The present invention relates generally to gas discharge lamps. More specifically, this invention relates to gas discharge lamps having a smaller diameter plasma lamp within a larger lamp.  
       SUMMARY  
       [0003]     In one aspect of the invention, a gas discharge lamp includes an outer glass tube having a phosphor coating on an inner surface of the outer glass. An inner glass tube is positioned inside the outer glass tube and formed of glass that is transparent to UV light. The inner glass tube contains a plasma-forming gas within an inner volume of the glass tube. A high frequency ballast is integral to the outer glass tube and configured to provide a high frequency AC waveform for driving electrodes configured for energizing the plasma-forming gas within the inner glass tube to form plasma paths therein. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]     Objects and advantages of the present invention will become apparent to those skilled in the art upon reading this description in conjunction with the accompanying drawings, in which like reference numerals have been used to designate like elements, and in which:  
         [0005]      FIG. 1  is a schematic representation of cross section at the center of the length of the bulb according to an embodiment of the present invention.  
         [0006]      FIG. 2  is a schematic representation of a side view of a hot cathode bulb end according to an embodiment of the present invention.  
         [0007]      FIG. 3  is a schematic representation of a side view of a cold cathode bulb end according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0008]     Gas discharge lamps, such as fluorescent lamps, generate light by creating a discharge or arc across an ionized gas within a glass tube. The traditional fluorescent lamp comprises a tube containing an inert gas and a material such as mercury vapor which, when ionized, can collide with electrons of a current flow across the electrodes of a lamp, and emit photons. These photons strike fluorescent material on the inner wall of the glass tube and produce visible light.  
         [0009]     Fluorescent lamps require a ballast to control operation. The ballast conditions the electric power to produce the input characteristics needed for the lamp. When arcing, the lamp exhibits a negative resistance characteristic, and therefore needs some control to avoid a cascading discharge. Both manufacturers and the American National Standards Institute specify lamp characteristics, which include current, voltage, and starting conditions. Historically, 50-60 Hz ballasts relied on a heavy core of magnetic material; today, most modern ballasts are electronic.  
         [0010]     Electronic ballasts can include a starting circuit and may or may not require heating of the lamp electrodes for starting or igniting the lamp. Prior to ignition, a lamp acts as an open circuit; when an arc is created the lamp starts, the entire ballast starting voltage is applied to the lamp. After ignition, the current through the lamp increases until the lamp voltage reaches equilibrium based on the ballast circuit. Ballasts can also have additional circuitry designed to filter electromagnetic interference (EMI), correct power factor errors for alternating current power sources, filter noise, etc.  
         [0011]     Electronic ballasts typically use a rectifier and an oscillating circuit to create a pulsed flow of electricity to the lamp. Common electronic lighting ballasts convert 60 Hz line or input current into a direct current, and then back to a square wave alternating current to operate lamps near frequencies of 2040 kHz. Some lighting ballasts further convert the square wave to more of a sine wave, typically through an LC resonant lamp network to smooth out the pulses to create sinusoidal waveforms for the lamp. See, for example, U.S. Pat. No. 3,681,654 to Quinn, or U.S. Pat. No. 5,615,093 to Nalbant.  
         [0012]     The square wave approach is common for a number of reasons. Many discrete or saturated switches are better suited to the production of a square wave than a sinusoidal wave. In lower frequency applications, a square wave provides more consistent lighting; a normal sinusoid at low frequency risks deionization of the gas as the voltage cycles below the discharge level. A square wave provides a number of other features, such as constant instantaneous lamp power, and favorable crest factors. With a square wave, current density in the lamp is generally stable, promoting long lamp life; similarly, there is little temperature fluctuation, which avoids flicker and discharge, damaging the lamp.  
         [0013]     In general, energy can be saved by avoiding the cycle of decay and recovery of ionization within the lamp. It is thus desirable to minimize the deionization of the gas during the oscillatory application of power to the electrodes. One way to accomplish this is through the use of higher frequencies, which can be accomplished, for example, in the manner described in International Publication No. WO 03/019992, in order to minimize the effects of harmonic distortion. Another problem with lamps, in particular T8 and larger lamps, is the diameter of the gas plasma. The current density in the plasma is better in a small diameter lamp. Also, the plasma must be heated, so a smaller space reduces the amount that the plasma needs to be reheated to maintain its temperature. The present invention contemplates having a smaller diameter plasma lamp centered in a T8 lamp with the phosphor coating on the inside of the larger outer glass tube to reduce the diameter of the gas plasma and create a more desirable and more efficient plasma.  
         [0014]     The present invention further contemplates that self ballasted gas discharge lamps may be configured with an integral ballast. In large commercial buildings and hi-rise buildings, much effort and cost is spent in replacing defective ballasts. The present invention contemplates a modified fluorescent light with the entire ballast included in one or both ends of the tube. This means that defective ballasts can be replaced by a bulb changer instead of an electrician. A ballast, according to the present invention, is small and has few components and is very efficient because of the very high operating frequency. (much greater than 100 KHz) The lamp will run cooler than a conventional ballasted lamp, making it possible to include the ballast either within the envelope or at one or both ends of the envelope. The present invention may be practiced with an external ballast connected in a manner that will be known to those in the art.  
         [0015]      FIG. 1  is a schematic representation of a cross section of one type of gas discharge lamp  250 . The cross section is at the center of the length of a bulb. In this view the generic concept of the invention can bee seen. The lamp  250  comprises a small diameter tube  40  in the center without any phosphorus coatings made of glass that is transparent to UV light and provides the UV light source. The outer glass  10  has the standard phosphor coating  20  on its inner surface  30 . The outer glass  10  blocks any UV radiation that may pass thru the phosphor coatings  20 .  
         [0016]      FIG. 2  is a schematic representation of a side view of gas discharge lamp  250  according to an embodiment of the invention. In this embodiment, the lamp  250  is a hot cathode comprising electrodes  260  configured for energizing a gas such as argon or xenon within the lamp  250  and forming plasma paths therein. In this particular embodiment, the lamp  250  is a T8 lamp having a diameter of approximately one inch, although those familiar with the art will recognize that other lamps and other diameters can be used.  
         [0017]     Lamp  250  preferably comprises an integral ballast  240 . The ballast  240  takes up some portion of the end of the lamp. In an exemplary embodiment, the ballast may include the following components, as shown generally in  FIG. 2 ; an inductor  300 , a typical capacitor  310 ,  330 , and  360 , a typical power transistor (semiconductor)  320  and surface mount components  340 ,  350 . The ballast shown is an exemplary ballast. Those of skill in the art will recognize other ballast designs that could work with the invention. The integral ballast  240  powers the bulb and its filaments  260 , and may require a small glass tube  270  to carry the filament wires  265  to the opposite end. The ballast  240  could also be included in an extended end cap  255  external to the lamp in keeping with an embodiment of the invention. Lamp  250  also includes an outer gas  280 , which may be dry nitrogen, which is preferably pumped to bring the gas to a near vacuum, or to a level known by those skilled in the art would know to reduce thermal conduction to required levels. An outer gas  280  can be any gas that is not very conductive to heat, or just a simple vacuum.  
         [0018]     Lamp  250  further comprises a small diameter tube  230  preferably in the center of the lamp  250 , or placed where those familiar with the art would specify, without any phosphorus coatings made of glass that is transparent to UV light and provides a UV light source. In a particular embodiment small diameter tube  230  has a diameter ⅜ of an inch or less. Lamp  250  further comprises outer glass  210  that has a phosphor coating  200  on its inner surface. The outer glass  210  blocks any UV radiation that may pass thru the phosphor coating  200 .  
         [0019]      FIG. 3 a  schematic representation of a side view of gas discharge lamp  450  according to another embodiment of the invention. As shown, the lamp  450  is a cold cathode comprising electrodes  460  configured for energizing a gas such as argon or xenon, or any gas known by those skilled in the art, within the lamp  250  and forming plasma paths therein, when energized by the ballast. Lamp  450  is a linear lamp, preferably with an integral ballast  470 . This embodiment uses cold cathodes and is therefore more efficient than the hot cathode embodiment shown in  FIG. 2 . The ballast  470  takes up a portion of the end of the lamp. Similarly numbered components in the  FIG. 2  are the same as components in  FIG. 3 . The integral ballast  470  powers the bulb, and may require a small glass tube (not shown) to carry the electrode wire to the opposite end. The ballast could also be included in an extended end cap external to the lamp in keeping with an embodiment of the invention.  
         [0020]     As above, lamp  450  comprises a small diameter tube  410  in the center without any phosphorus coatings made of glass that is transparent to UV light which provides the UV light source. An outer glass  435  has the standard phosphor coating  400  on its inner surface  480 . The outer glass  435  blocks any UV radiation that may pass thru the phosphor coatings  400 . Lamp  450  also includes an outer gas  480 , which may be dry nitrogen, which is preferably pumped to bring the gas to a near vacuum, or to a level known by those skilled in the art would know to reduce thermal conduction to required level. An outer gas  480  can be any gas that is not very conductive to heat, or just a simple vacuum. A small wire (not shown) may pass thru this vacuum to power the far end of the tube.  
         [0021]     The far end of the bulb may have a single plastic dummy pin for mechanical positioning and retention of the tube. This is done so that customers can place the tube in only one position. Alternatively, both ends of the lamp could be powered, with only one end having the pins connected. Other connection and mounting methods may be easily developed by those skilled in the art.  
         [0022]     It will be appreciated by those of ordinary skill in the art that the invention can be embodied in various specific forms without departing from its essential characteristics. The disclosed embodiments are considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims, rather than the foregoing description, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced thereby.  
         [0023]     It should be emphasized that the terms “comprises”, “comprising”, “includes”, and “including”, when used in this description and claims, are taken to specify the presence of stated features, steps, or components, but the use of these terms does not preclude the presence or addition of one or more other features, steps, components, or groups thereof.