Patent Application
20060038496
The present invention relates to discharge lamps having a source of emission in the wavelength range in the UV-A radiation. In particular, the present invention relates to fluorescent lamps having a gas discharge UV-A radiation source and emitting in the visible electromagnetic spectrum.
Mercury vapor discharge fluorescent lamps have been used extensively for lighting purposes. In such lamps, a small amount of mercury and an inert gas, such as argon, krypton, or xenon, are contained in a sealed glass tube having an electrode at each of its ends. During operation, a discharge is generated between the electrodes, and the mercury atoms are excited to a high-energy state. Upon returning to the ground state, the mercury atoms produce ultraviolet (“UV”) radiation, which consists essentially of emission at 254 nm and 185 nm. In order to convert this UV radiation to useful light in the visible wavelength range, one or more phosphors are provided on the inner wall of the glass tube to absorb this UV radiation and emit in the wavelength range. The terms “light” and “electromagnetic (‘EM’) radiation” without a qualifier are used herein interchangeably to denote EM radiation having wavelengths in the range from about 100 nm to about 1 mm. UV-A means UV radiation having wavelengths in the range from about 300 nm to about 400 nm.
The energy efficiency of mercury vapor discharge fluorescent lamps are low because of the large difference between the wavelengths of radiation emitted by mercury and those of light emitted by the phosphors. In addition, mercury in lamps that are finally discarded presents a source of pollution.
U.S. Pat. No. 6,040,658 describes a mercury-free discharge lamp wherein UV-A emission having wavelength of about 306 nm is obtained from excited OH radicals, which are formed from dissociation of alkali earth metal hydroxides, such as Ca(OH)2 or Mg(OH)2, or of water vapor. Although the emission of excited OH radicals is closer to the visible emission of most useful phosphors than that of mercury, there still is a large difference.
Therefore, it is desirable to provide a source of exciting radiation having wavelength closer to the emission of useful phosphors. In addition, it is also desirable to provide fluorescent lamps incorporating such a source of radiation for improved energy efficiency.
The present invention provides a mercury-free EM radiation source emitting radiation in the wavelength range from about 254 nm to about 410 nm. In particular, the radiation source emits in the wavelength range from about 300 nm to about 400 nm.
According to one aspect of the present invention, a light source comprises an EM radiation source emitting first EM radiation in the wavelength range from about 254 nm to about 410 nm, and at least a photoluminescent material excitable by the first EM radiation to emit a second EM radiation in the visible wavelength range.
According to another aspect of the present invention, visible light is generated by a method that comprises: (a) providing an EM radiation source emitting first EM radiation in the wavelength range from about 254 nm to about 410 nm; and (b) disposing at least a photoluminescent material that absorbs the first EM radiation and emits a second EM radiation in the visible wavelength range.
Other features and advantages of the present invention will be apparent from a perusal of the following detailed description of the invention and the accompanying drawings in which the same numerals refer to like elements.
The present invention provides a mercury-free EM radiation source emitting radiation in the wavelength range from about 254 nm to about 410 nm. In particular, the radiation source emits in the wavelength range from about 300 nm to about 400 nm. The radiation source is a gas discharge containing materials that are capable of generating at least one of oxygen-, nitrogen-, and carbon-containing radicals. In one embodiment, these radicals are generated by bombarding materials containing oxygen, nitrogen, or carbon with charged species that may be generated by, for example, an electrical discharge or a high-frequency EM field. The radicals in the discharge are in high-energy excited state, emitting EM radiation upon returning to a lower energy state. Non-limiting examples of high-energy radicals that emit EM radiation in the range from about 254 nm to about 400 nm are OH, CO, CO+, CO2+, CN, CN+, NH, NO, N2O+, and C2. These radicals exhibit strong emission at the wavelength shown in Table 1, which also shows exemplary sources for the particular species.
(See; e.g., R. W. B. Pearse and A. G. Gaydon, “The Identification of Molecular Spectra,” Chapman and Hall, London, 1976.)
A fluorescent lamp tube with associated electrodes was evacuated, and then filled with argon, nitrogen, and water vapor, each having an individual vapor pressure of about 2 torr (or 267 Pa), 0.2 torr (or 26.7 Pa), and 0.2 torr (or 26.7 Pa), respectively. An electrical discharge was established in the tube, and emission spectra were obtained at time 0, 5, 7, 9, 25, 30, and 35 minutes after an electrical potential of 200 V was applied to the electrodes. The emission spectra are shown in
Mercury-free fluorescent lamps using at least one of the excited radicals disclosed above as the source of exciting radiation for photoluminescent materials (or phosphors) can improve the energy efficiency of fluorescent lamps because the wavelength of exciting radiation is closer to the phosphor emission wavelength (smaller Stokes shift) than the wavelength of mercury vapor discharge. In addition, phosphors can be selected that strongly absorb exciting radiation from a particular high-energy radical, further increasing the lamp energy efficiency. Many such phosphors absorb strongly in the wavelength range from about 300 nm to about 410 nm, and thus have not been optimally used in conjunction with the mercury emission at 254 nm in conventional mercury discharge-based fluorescent lamps. Non-limiting examples of such phosphors are (1) the blue emitting phosphors (Sr,Ca)10(PO4)6Cl2:Eu2+; Sr2P2O7:Eu2+; (Sr,Mg)2P2O7:Eu2+; and Ba0.07Mg2AlzO3/2z+3:Eu0.132+, where 14≦z≦25; (2) the green emitting phosphors 2SrO.0.84P2O5.0.16B2O3:Eu2+; Sr2Si3O8.2SrCl2:Eu2+; Sr4Al4O25:Eu2+; and Ba0.8Mg1.93Al16O27:Eu0.22+,Mn2+; (3) the green-yellow emitting phosphor Y2SiO5:Ce3+,Tb3+; and (4) the red emitting phosphors 6MgO.As2O5:Mn4+ and 3.5MgO.0.5MgF2.GeO2:Mn4+.
In one embodiment, the construction of a mercury-free fluorescent lamp of the present invention is similar to that of a conventional fluorescent lamp.
In another embodiment, the electrical discharge that provides charged species for generating excited mercury-free charged radicals of the present invention is generated by an induction coil at high frequency. The coil generates a high-frequency magnetic field, which produces a magnetically induced plasma discharge. Such a source of discharge has been put into practice in electrodeless discharge lamps. For example, U.S. Pat. Nos. 4,262,231; 5,952,791; 5,959,405; 6,051,922; and 6,137,236; which are incorporated herein by reference, show various embodiments of electrodeless discharge lamps. One or more of the materials, which are listed in Table 1 above, that can generate excited radical species when bombarded by other species of the plasma, which excited radical species emit EM radiation in the UV range upon returning to a less excited state, can be used as a component of the filling gas in such electrodeless lamps to practice the present invention. Frequencies in the range of greater than about 2 MHz, preferably greater than about 2.5 MHz, can be used to generate the magnetically induced plasma discharge.
While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations, equivalents, or improvements therein may be made by those skilled in the art, and are still within the scope of the invention as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004125185 | Aug 2004 | RU | national |
