The present invention is related to generating light and more particularly to plasma lamps.
High density plasma lamps may be used as a source of bright, broadband light. Conventional high density plasma lamps typically rely on a plasma of a low partial pressure noble gas (<0.5 bar) to vaporize metal salts that create a bright source of broadband light. The ignition process can be initiated by coupling radio frequency (RF) energy into the interior of the enclosure. The power density of the coupled RF energy must be sufficient to ionize the low pressure noble gas. The ionized species is accelerated within the RF field causing heating, evaporation, and ionization of the metal salt. The ionization of the primary gas creates further species of ionized gases until a final ignition of a sustained plasma of the primary gas plus evaporated metal halide is achieved.
A plasma lamp includes a capsule with a gas contained within the capsule and an ignition source to ionize the gas to produce a light emitting plasma. The ignition source includes field defining conductors within the capsule and a radio frequency source external to the capsule. The radio frequency source and the field defining conductors are configured so that the field defining conductors will produce electric fields in response to RF energy from the radio frequency source and the electric field ionizes at least a portion of the gas.
An issue that exists with conventional plasma lamps is that metal halides, by their nature, have low photon throughput in the ultra-violet (UV) and deep UV (DUV) region of the spectra, as the photons with UV/DUV wavelengths created within the plasma are also reabsorbed by the plasma. Thus, the use of ionized metal halide salts in conventional plasma lamps limits the lower wavelengths of light that may be emitted by the plasma lamps to wavelengths greater than UV, e.g., greater than 350 nm. Thus, in order to produce light with wavelengths in the UV and/or DUV regions, a plasma lamp should not include metal salts. The absences of metal salts in plasma lamps, however, requires the ignition of a plasma gas at higher pressures, e.g., greater than 0.5 bar, which is difficult to achieve. For example, ionization of a high pressure primary gas such as xenon requires a high electrical field making a high pressure xenon plasma lamp impractical. Moreover, while a plasma lamp may use low pressure gas for ignition at a more practical electrical field, low pressure gas does not produce a light with a continuum of spectra. Thus, the use of ionized metal salts or low pressure gas in conventional plasma lamps limits the useful spectra of light that is produced.
Plasma lamp 100 overcomes the issues of limited UV wavelengths of light by eliminating the metal salts and using an ignition source 130 that includes a radio frequency (RF) source 140 external to the capsule 110 and a plurality of field defining conductors 150 within the capsule 110. With the use of the field defining conductors 150 within the capsule 110, the gas may be easily ignited despite being held at high pressure, e.g., greater than 0.5 bar. The RF source 140 and the field defining conductors 150 are configured so that the interaction between the RF energy from the RF source 140 and the field defining conductors 150 will create a localized high electric field that ionizes at least a portion of the gas in the gaseous environment 120, i.e., the gas that is in the vicinity of the field defining conductors 150 is ionized. The field defining conductors 150 are electrical conductors that include a radius of curvature that is small enough and of sufficiently small area that a large localized electric field is generated from the interaction with the RF energy from the RF source 140.
By way of example, the field defining conductors 150 may be filamentary conductors or thin planar conductive sheets. An example of a filamentary conductor that may be used as the field defining conductors 150 is a carbon nano-tube bundle or carbon nano-fibers. Carbon nano-tubes, for example, may be single or multi-walled and may have a diameter of e.g., 1 nm, 3 nm, 7 nm, 15 nm, 30 nm, 60 nm, 120 nm, 200 nm, or possibly larger. The carbon nano-tubes may have lengths of e.g., 1 um, 3 um, 7 um, 15 um, 30 um, 60 um, 120 um, 200 um, or possibly longer. The amount of carbon nano-tube material may be, e.g., nano-grams, micron-grams, milli-grams, or possibly more. It may be desirable for the carbon nano-fibers to retain their metal (e.g., Fe, Ni, etc.) catalyst material. The small diameter of the carbon nano-tubes and small area at the end regions may be used to produce a large electric field from the interaction with the RF energy from the RF source 140. Another example of filamentary conductors that may be used as field defining conductors 150 are filaments of doped boron nitride or other suitable materials that can withstand the resulting environment, including heat, when the large electric field and resulting plasma are produced. An example of thin planar conductive sheets that may be used as field defining conductors 150 is, e.g., planar sheets of carbon commonly referred to as graphene. Graphene includes edges of small diameter that may be used to produce a large electric field from the interaction with the RF energy from the RF source 140.
It should be understood that the plasma lamp 100 may include additional components, such as a housing, optical elements, and circuitry, which are well known in the art.
The use of noble gases or noble gas halides without the presence of metal salts in the plasma map is advantageous to produce light having a broad spectrum including visible light as well as UV components of less than 250 nm and more particularly less than 200 nm.
Although the present invention is illustrated in connection with specific embodiments for instructional purposes, the present invention is not limited thereto. Various adaptations and modifications may be made without departing from the scope of the invention. Therefore, the spirit and scope of the appended claims should not be limited to the foregoing description.
This application claims priority under 35 USC 119 to U.S. Provisional Application No. 61/619,778, filed Apr. 3, 2012, and entitled “Plasma Lamp Ignition Source” which is incorporated herein by reference in its entirety.
Number | Date | Country | |
---|---|---|---|
61619778 | Apr 2012 | US |