Electric lamp and discharge devices: systems – Pulsating or a.c. supply
Reexamination Certificate
2000-07-20
2002-09-03
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
C315S250000, C315S260000
Reexamination Certificate
active
06445137
ABSTRACT:
FIELD OF TECHNOLOGY
This invention concerns light source equipment that includes what is called a dielectricbarrier discharge lamp, which is a type of discharge lamp used, for example, as a source of ultraviolet radiation for photochemical reactions, in which excimer molecules are formed by dielectric-barrier discharge, and which uses light emitted from the excimer molecules.
BACKGROUND OF TECHNOLOGY
Technical literature explaining the technology involved in the dielectric-barrier discharge lamps with which this invention is concerned can be found in, for example, JPO kokai patent report H2-7353. This document describes an emitter that produces light by causing the formation of excimer molecules by means of a dielectric barrier discharge (also known as ozonizer discharge or silent discharge; see Denki Gakkai, “Discharge Handbook,” revised edition, 7th printing, June 1989, p. 263) in a discharge chamber filled with a discharge gas that forms excimer molecules, and using the light radiated by those excimer molecules.
Dielectric-barrier discharge lamps as described above, and light source equipment containing such lights, have a number of advantages not found in conventional low-pressure mercury discharge lamps and high-pressure arc discharge lamps, and so have a variety of potential applications. One of the most important of these, given the mounting interest in the issue of environmental pollution in recent years, is the decontamination of materials by means of photochemical reactions using ultraviolet radiation. Consequently, there is unusually strong demand for dielectric-barrier discharge lamp light source equipment with high outputs and broad areas of illumination.
One proposal in line with this demand is found in JPO kokai patent H4-229671, which describes a constitution that enlarges the light source and expands the area of illumination by lighting multiple dielectric-barrier discharge lamp in parallel. There are, however, a number of major, unresolved problems in such attempts to use conventional technology. The first problem is that it is difficult, when illuminating a broad area, to make the illumination energy density uniform or to make the light adjustable. The second problem is greater economy is sought as the output is increased and the area of illumination is enlarged, or in other words as the electrical power of the equipment is increased. The third problem is that, as the output is increased and the area of illumination is enlarged, the heat generated by the lamp increases and its service life grows shorter.
Now, the reason for the necessity of being able to adjust the light within the first problem is simply explained. The function of treating materials using ultraviolet light from dielectric-barrier discharge lamps depends on highly complicated and precise photochemical reactions; in order to obtain the desired treatment effect in materials of large area, it is necessary that the illumination energy density distribution not be greater or less than the desired distribution. In the event that the illumination energy density is inadequate, the effect of illumination is low, which is clearly a problem. In the event that the illumination energy density is excessive, problems are caused by excessive reactions that go beyond the proper limits. For example, the breakdown products of the ultraviolet light illumination may react again and undergo unintended molecular synthesis, or an uneven layer of impurities may be formed on the surface of the material being treated. Accordingly, there is a permissible range that depends on the sort of treatment to be performed, and to avoid illumination energy density distribution that is not greater or less than the desired distribution, the ideal dielectric-barrier discharge lamp should have the function of adjusting the illumination energy density to fit the permissible range.
Moreover, in dielectric-barrier discharge lamps, as in other lamps, there are variable factors in the intensity of light emitted. The first variable factor is variation of the period of time needed for electrical and thermal stabilization after the lamp is lighted. The second variable factor is the period between the lamp being in new condition to the end of its service life. The function of adjusting the illumination energy density is needed to correct for these variables and maintain the desired illumination energy density.
A proposal to resolve the first problem mentioned above, which is the difficulty when illuminating a broad area or making the illumination energy density uniform and making the light adjustable, was made in JPO kokai patent H8-146198, but that did not include positive solutions to the second problem or the third problem.
In order to resolve the third problem mentioned above, it is necessary to improve the lighting efficiency of the lamp. The conditions for improvement of the lighting efficiency of lamps are explained below.
Dielectric-barrier discharge lamps (B, B
1
, B
2
. . . ) have a discharge plasma space (G) and one or two dielectrics sandwiched between electrodes (Ea, Eb).
FIG. 1
shows a single dielectric-barrier discharge lamp with two dielectrics (D). In
FIG. 1
, by the way, the lamp seal (
6
) also serves as the dielectric (D).
When lighting up the dielectric-barrier discharge lamp (B), a high-frequency, alternating current of, for example 10 to 200 kHz and 2 to 10 kV is impressed on the electrodes (Ea, Eb). However, because of the dielectric (D) between the discharge plasma space (G) and the electrodes (Ea, Eb), current does not flow directly from the electrodes (Ea, Eb) to the discharge plasma space (G); the current flows by means of the action of the dielectric (D) as a condenser. In other words, a charge equal in size and opposite in sign to that on electrodes (Ea, Eb) is induced on the discharge plasma space side of the dielectric (D) because of polarization of the dielectric; The discharge occurs between the dielectric (D) that faces across the discharge plasma space (G).
Little current flows along the discharge plasma space (G) side of the dielectric (D); when discharge occurs, the charge induced on the discharge plasma space (G) side of the dielectric (D) is neutralized by the charge moved by the discharge, and the electrical field within the discharge plasma space (G) is reduced. For that reason, the current stops even if the voltage continues to be impressed on the electrodes (Ea, Eb). But when the voltage impressed on the electrodes (Ea, Eb) rises again, the discharge current continues. When the discharge ceases after having occurred, there is no further discharge until the polarity of the voltage impressed on the electrodes (Ea, Eb) has reversed.
In the case of a dielectric-barrier discharge lamp in which xenon gas, for example, is sealed, the xenon gas is dissociated into ions and electrons by the discharge, and becomes xenon plasma. When the xenon plasma is excited to a specified energy level, excimer molecules are formed within the plasma. Xenon excimers divide after a certain lifespan, but the energy released at that time is emitted as a photon of vacuum ultraviolet wavelength. To make a dielectric-barrier discharge lamp work efficiently as a vacuum ultraviolet light source, it is necessary to form the excimer molecules efficiently.
The greatest obstacle to efficient formation of excimer molecules during discharge is the excitation of the discharge plasma to energy levels that do not contribute to the formation of excimer molecules.
The movement of discharge plasma electrons immediately after discharge begins is collective, and the energy is high but the temperature is low. In this state, the discharge plasma has a high probability of transition to the resonant state required for formation of excimer molecules. If the discharge time is prolonged, however, the movement of the plasma electrons gradually becomes thermal. That is, it reaches a state of thermal equilibrium known as a Maxwell-Boltzmann distribution; the plasma temperature rises, and there is an increased probability of transition to a state of hi
Asahina Takashi
Hirose Ken-ichi
Okamoto Masashi
Nixon & Peabody LLP
Safran David S.
Ushiodenki Kabushiki Kaisha
Vu David
LandOfFree
Dielectric barrier discharge lamp apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Dielectric barrier discharge lamp apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dielectric barrier discharge lamp apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2871766