Electric lamp and discharge devices: systems – Pulsating or a.c. supply – Transformer in the supply circuit
Reexamination Certificate
2000-10-13
2002-11-12
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
Transformer in the supply circuit
C315S309000, C315S276000, C315S112000, C315S117000
Reexamination Certificate
active
06479947
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to fluorescent lamps and more particularly to an ultraviolet fluorescent lamp assembly comprising a unique drive circuit and housing.
BACKGROUND OF THE INVENTION
The fluorescent lamp is a gas discharge tube that is used for lighting purposes. Generally, the inner surface of the wall of the tube is coated with light-emitting substances—usually fluorescent or phosphorescent metallic salts, and the tube is filled with mercury vapor at extremely low pressure and has filaments at each end of the tube. The light of the fluorescent lamp is not produced by an incandescent body (such as the filament of an ordinary electric lamp), but is emitted as a result of the excitation of atoms (namely, those of the mercury vapor and the fluorescent coating) and is extremely economical. The electrons ejected from the cathode filaments collide with the mercury atoms of the vapor and cause the mercury atoms to emit radiation which consists for the most part of ultraviolet rays, which are invisible. The ultraviolet light strikes the fluorescent substance with which the wall of the tube is coated and, depending upon the coating, may cause the substance to emit radiation with a longer wavelength in the visible rage of the spectrum—i.e., the coating may transform the invisible rays into visible light.
The conventional fluorescent lamp has to be operated with a choke (normally referred to as a ballast), which prevents a harmful rise in voltage and serves to ignite the lamp. For this purpose a starter circuit comprising a small auxiliary glow lamp provided with a thermal contact is usually connected in parallel with the main lamp. When the current is switched on, the glow lamp first lights up (the thermal contact is now open). This causes the contact to warm up and close, with the result that the glow lamp is short-circuited and the cathodes of the main lamp receive the full current. The thermal contact then cools and breaks, providing a voltage surge which is high enough to initiate the discharge in the fluorescent lamp itself. Because it is bypassed by the main lamp, the small auxiliary glow lamp then ceases to function.
Ultraviolet fluorescent lamps are often used in museum and other displays where powerful lighting is required to properly irradiate and display fluorescent mineral specimens. Fluorescent lamps are used with special ultraviolet filters that transmit the ultraviolet light and absorb the visible light that is generated by the lamps. However, most ultraviolet fluorescent lamps in use today have short useful life spans, and it is most commonly due to the inability of conventional drive circuits with conventional starter circuits to handle the high number of on-off cycles necessary in such a museum or other display. Another drawback of the currently available lamps is that no manufacturer of commercial ultraviolet lights uses a high output lamp.
Many prior inventors, such as Ewest and Yamamoto, have recognized the need to improve the starting and operating efficiency of fluorescent lamps. However, these prior art patents are directed simply to alternative designs of starter circuits. Ewest, in U.S. Pat. No. 1,961,749, discloses a gaseous electric discharge device which uses an auxiliary electrode in addition to the main electrode at one end of he lamp tube. This auxiliary electrode in proximity to the main electrode serves as a starter “glow lamp” component for the main lamp. Ewest's device also uses a high frequency apparatus to ionize the gas within the tube.
Yamamoto et al., in U.S. Pat. No. 5,107,183, disclose a fluorescent lamp which also uses a special arrangement of electrodes at one end or both ends of the lamp to constitute a starter “glow lamp” component. Both Ewest's device and Yamamoto's device, because they use the same current supply to start the lamp as well as to maintain operation of the lamp, would have the same short lifespans of other extant devices.
SUMMARY OF THE INVENTION
One aspect of the present invention comprises a drive circuit for an ultraviolet (UV) lamp that does not use a conventional starter circuit.
The preferred embodiment of the drive circuit is designed around three unique custom-made lamps, and each circuit comprises at least one custom-made generally tubular lamp (sometimes called a bulb) that can be either short wave (made from a clear quartz tube that has a high UV-C transmission at 253.7 nm of about 90%), medium wave (made from a special erythemal glass with a UV-B phosphor on the inside of the lamp that will transmit the 306 nm wavelength), or long wave (made from a common soda-lime glass tube with a UV-A phosphor on the inside of the lamp that will transmit a peak output at 352 nm). Each lamp is a Rapid Start High Output lamp operating at the maximum amount of lamp current for that diameter and length of lamp. Each lamp has tungsten wire filaments on each end. In the making of the lamp the filaments are coated with an electron-emissive material (e.g., barium, strontium, and calcium as compounds) to turn them into lamp cathodes. The cathodes are designed for High Output lamp current. In addition there are wire or metal anodes on each cathode, the anodes helping prolong the life of the emissive material. Each lamp has a standard bi-pin base at each end, and in the preferred embodiment, all lamps are the same length (e.g., 22 ⅜ inches from pin to pin) so that they are interchangeable within the entire assembly.
In addition to the lamp, the preferred embodiment of the drive circuit also comprises at least one each of a ballast subcircuit with ballast element and a transformer subcircuit with transformer element, and a lockout relay. The present invention of the drive circuit need not include the lockout relay; however, the relay is included in the preferred embodiment as an additional check upon the safe and correct operation of the drive circuit. The lockout relay prevents the high voltage of the ballast from being supplied to the lamp cathodes until the transformer subcircuit is powered and the lamp cathodes have been pre-heated.
The ballast element, which may be any type of appropriate ballast (such as an electronic ballast, but in the preferred embodiment is a conventional electromagnetic ballast), of the ballast subcircuit supplies high voltage (arc voltage) between the lamp cathodes at each end of the lamp. The ballast used in the preferred embodiment is a conventional electromagnetic ballast, but the filament windings are not used, and only one wire from each end of the ballast (high voltage) is connected to each end of the lamp. (Normally two wires from each end are connected to two pins of each end of the lamp.) For pre-heating the cathodes, the preferred embodiment of the drive circuit also comprises a separate transformer subcircuit which is used to supply low voltage (starter voltage) to the lamp cathodes, and which precludes the necessity of a conventional starter circuit. The transformer has two secondaries and four output leads, two per secondary, which lead to the lamp cathodes. In this way, cathode heat is supplied to each end of the lamp separate from the ballast. The transformer is always powered up before the high voltage from the ballast is supplied.
The average rated life of the lamp is greatly extended by having the filaments (cathodes) heated first before the high voltage (arc current) is applied. Heating the cathodes causes a space charge of electrons to form around the cathode filaments, the cloud of electrons helping to repel the heavy mercury (Hg) ions from impinging on the electron emissive material that is on the cathodes. Being repelled, the ions do not knock off emissive material that is on the cathodes. The lamps also have two anode wires on either side of the cathodes, which attract the ions away from the cathodes. This helps to prolong the life of the lamp, since the life of a fluorescent lamp is a function of the amount of emissive material that is on the cathodes. The resulting lamp life should approximate the continuous burning rated life
Lee Wilson
Oliver Polly L.
Wong Don
LandOfFree
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