EP0549046B1 - Lighting system and high pressure glow discharge lamp to be used in said system - Google Patents

Description

The invention relates to a lighting system which comprises a high-pressure glow discharge lamp with a planar, vacuum-tightly sealed discharge vessel, the discharge vessel enclosing a discharge space containing a gas filling forming excimers, the parallel walls of which are formed by a dielectric, the surfaces of the walls facing away from the discharge space being provided with planar electrodes at least one of these walls with an associated electrode is at least partially transparent to the radiation generated, the surfaces of the walls facing the discharge space being arranged at a distance d from one another, and the gas filling containing one of the noble gases Xe and Kr as excimer formers, wherein the excimer generator has a partial pressure P which is less than a limit value Pg, into which lighting system the lamp is fed in an operating state with an AC voltage with operating frequency f.

The invention also relates to the use of such a lighting system and to a high-pressure glow discharge lamp for such a lighting system.

A dielectrically impeded glow discharge (also called "silent discharge") is generated in a high-pressure glow discharge lamp at a relatively high gas pressure. In the case of these discharges, a gas filling emitting radiation upon electrical excitation and at least one dielectric are present between two planar electrodes which are completely or partially transparent. The electrical supply takes place with AC voltage. The discharge principle is described, for example, in the article by B. Eliasson and U. Kogelschatz, Appl. Phys. B46 (1988) 299-303.

A lamp suitable for use in a lighting system of the type mentioned at the outset is known, for example, from EP-A 0 324 953 (see also EP-A 0 254 111, 0 312 732 and 0 371 304). In this description and in the claims, a planar discharge vessel which is sealed in a vacuum-tight manner is understood to mean a discharge vessel which is in any case almost parallel Walls whose dimensions are large compared to the distance between these walls and a vacuum-tight side wall, the walls can be plane-parallel or coaxial and where a stroke distance, also called discharge length, from the distance (d) between the inner surfaces of the Walls is determined.

For the walls of the discharge vessel, a dielectric, i.e. electrically non-conductive, material used. At least one of the parallel walls is transparent to the radiation generated and materials such as e.g. Glass, quartz, which can be UV-transparent, or the fluorides of magnesium or calcium, which are transparent for very short-wave radiation. The dielectrics mentioned are generally dielectric and chemically resistant to the gas filling. The flat electrodes can be made of metal, e.g. Metal plates or metal layers can be formed. Transparent electrodes can be used as mesh or grid electrodes, e.g. Wire meshes or grid electrodes, or also as transparent metal layers (5 - 10 nm) or electrically conductive oxide layers.

The invention has for its object to provide a lighting system that has a high radiation yield, and also to enable extensive homogeneous flat radiation sources with high radiation yield.

• worin für Xenon gilt A = 0.3 bar, B = 6 bar und C = -1.3 mm⁻¹, mit
• D = 200 kHz und E = -1.47 für d ≤ 2.75 mm, und
• D = 350 kHz und E = -2 für d > 2.75 mm,
• und worin für Krypton gilt A = 0.75 bar, B = 150 bar und C = -2.3 mm⁻¹, mit D = 160 kHz und E = -1.74.

This object is achieved with a lighting system of the type mentioned at the outset in that the limit value Pg is smaller depending on the operating frequency f deviates more from a frequency f _M , the limit value having a maximum P _M , where P _M = A + B * exp ( C * d) and f _M = D * d ^E ,

• where for xenon applies A = 0.3 bar, B = 6 bar and C = -1.3 mm⁻¹, with
• D = 200 kHz and E = -1.47 for d ≤ 2.75 mm, and
• D = 350 kHz and E = -2 for d> 2.75 mm,
• and where for krypton applies A = 0.75 bar, B = 150 bar and C = -2.3 mm⁻¹, with D = 160 kHz and E = -1.74.

The following description explains the invention with reference to the drawings. The relationship between the limit value Pg for the partial pressure of the excimer former and the operating frequency f der is schematically shown in Figure 1 AC voltage shown. Figure 2 shows schematically the relationship between the operating voltage amplitude U and the total pressure Pges of the gas filling. Pges is the sum of the partial pressures of the excimer generator and any buffer gas (Pp) used.
Figure 3 shows an embodiment of a lamp for use in a lighting system according to the invention. Figure 4 shows a single part of the lamp of Figure 3.

The invention is based on the insight that an excellent operating range with respect to the operating parameters P and f exists for a discharge length d between 0.05 and 10 mm, which is shown hatched in FIG. 1. The partial pressure P of the excimer former is limited by a limit value Pg which has a maximum P _M at an operating frequency f _M. The selection of the operating parameters in the hatched area enables the voltage amplitude U to be set to a value within an interval ΔU, with one ignition occurring per half-wave of the AC voltage (see Figure 2). Under these circumstances, the lamp assumes a homogeneous operating condition. The interval is limited by a voltage amplitude U 1 below which the discharge extinguishes, and a voltage amplitude U 2 above which more than one ignition per AC half-wave takes place.

Given the maximum P _M for the limit value and the frequency f _M, where the limit value has its maximum, the operating range is easy to determine. In addition to the operating point (P _M , f _M ), operating points at this frequency f _M with operating pressures P less than P _M also belong to the operating range. On the basis of these operating points, it is easy to determine in each case at constant operating pressure P within which frequency range an interval still exists, with one ignition occurring per half-wave of the AC voltage.

Outside of this operating range, no diffuse, homogeneous discharge is generally formed at higher pressures, but the discharge contracts in a large number of narrowly delimited filaments distributed over the surface. A filamented discharge mode has a lower radiation yield and is also undesirable for lighting applications because of the inhomogeneity that arises. If the above conditions for the partial pressures are met Lighting systems with large-area high-pressure glow discharge lamps, for example DIN A4-sized or even larger flat lamps, which have both a homogeneous discharge mode and a high radiation yield.

When Xe is selected as the excimer former, predominantly 172 nm emission in the 165-195 nm range is achieved; when Kr is selected as the excimer former, 146 nm emission in the 135-165 nm region is predominantly achieved. The area is based on a band base of approx. 10%.

It is advantageous if the operating point (P, f) is close to the operating point (P _M , f _M ). The lamp then has a relatively high radiation yield.

It has been found that homogeneous operating conditions and forms of training are expanded by the addition of the smallest amounts of electronegative gas components which act as electron attachers. Any attached gas component can be used, provided that the excimer kinetics are not changed in such a way that an excimer process competing to produce Xe or Kr excimers or other loss processes are added, which lead to a noticeable loss of efficiency compared to the pure noble gas system to lead. In an advantageous embodiment of the lighting system according to the invention, the gas filling contains electronegative gases with a partial pressure P _D between 5x10⁻⁵ and 5x10⁻⁴ times the partial pressure of the excimer former. For example, additions of O₂ in admixture cans within the above range have proven to be practically without influence for the efficiency of the Xe or Kr excimer radiation, although the formation of a homogeneous discharge mode is promoted.

A very advantageous embodiment of a lighting system according to the invention solves the problem that the areal expansion of the lamp is limited by the total pressure of the gas filling (substantially below 1000 mbar). If a vessel size limited by the wall thickness and the maximum tolerable mechanical stresses occurring in the material is exceeded, implosion can occur. This limit is at a total pressure of approximately 100 mbar and wall thicknesses of 2-3 mm with a typically 10 cm linear expansion of the walls. Large-area high-pressure glow discharge lamps are realized according to the invention if the gas filling is additionally used as a buffer gas when Xe is used Excimer former contains at least one of the noble gases He, Ne, Ar and Kr, and when Kr is used as the excimer former contains at least one of the noble gases He, Ne and Ar. The atomic mass of the buffer gas is considerably smaller than the atomic mass of the excimer former. The total pressure of the gas charge Pges is increased by the added buffer gas without impairing the homogeneous operating behavior.

Good results are obtained in practical implementations of the above-mentioned embodiments, the total pressure Pges of the gas filling being less than four times the partial pressure P of the excimer former.

A preferred embodiment of a lighting system according to the invention is characterized in that the discharge vessel has an inner phosphor layer. When using phosphors (for example described by Opstelten, Radielovic and Verstegen in Philips Tech. Rev. 35, 1975, 361-370), large-area, homogeneously radiating light sources can be produced, which can be used as backlighting of large-area LCDs, luminous walls, display elements and the like. Ä. Find.

Another preferred embodiment of a lighting system according to the invention is characterized in that the discharge vessel has fluorescent vessel walls.

Embodiments of lighting systems according to the invention are explained below with reference to Figures 3 and 4. FIG. 3 shows schematically and in section a high-pressure glow discharge lamp 1 suitable for use in a lighting system according to the invention. The lamp 1 has a planar discharge vessel 2, which is sealed in a vacuum-tight manner and which encloses a discharge space 3 containing a gas filling which forms excimers. The discharge vessel 2 has parallel walls 4 _A , 4 _B made of a dielectric, in this case quartz glass plates with a thickness of 2 mm. The walls 4 _A , 4 _{B of} the discharge vessel 2 are connected to one another by a cylindrical quartz spacer 5 with a diameter of 40 mm. The quartz spacer ring 5 has a pump nozzle 6 with which the discharge vessel 2 is evacuated and filled. The parts 4 _A , 4 _B , 5, 6 of the discharge vessel 2 are joined together by glass soldering technology. The surfaces 7 _A , 7 _{B of} the walls 4 _A , 4 _B facing away from the discharge space 3 are included planar electrodes 8 _A , 8 _B provided. The lamp 1 has a coupling-out electrode 8 _B, which is partially transparent to the generated radiation, made of a lattice structure made of gold with web widths of 0.5 mm and a mesh size of 1.5 mm. Electrode 8 _B , shown in view in Figure 4, is applied to the surface by pyrolytic sedimentation. The other electrode 8 _A is made of aluminum and is evaporated onto the wall 4 _A. Otherwise, the latter electrode 8 _{A can} also have a lattice structure, for example made of gold. The surfaces 9 _A , 9 _{B of} the walls 4 _A , 4 _B facing the discharge space 3 are arranged at a distance d of 2 mm from one another. The gas filling contains Xe as an excimer. In the lighting system, the lamp 1 is supplied in an operating state with an AC voltage from an electrical supply, not shown. With Xe as excimer former and distance d = 2 mm, the limit value Pg has a maximum value P _M of 0.75 bar at a frequency f _M of 72 kHz.

In this exemplary embodiment, the gas filling is composed as follows. The partial pressure of the excimer generator is 0.5 bar (i.e. below P _M ). The gas filling also contains neon as a buffer gas with a partial pressure of also 0.5 bar and a doping of O₂ with a partial pressure of 0.1 mbar. The total pressure (approximately 1 bar) of the gas filling is less than four times the partial pressure of the excimer generator. The partial pressure P _{D of} the O₂ doping is 2x10⁻⁴ times the partial pressure of the excimer.

When the lamp is operated with a sinusoidally alternating high voltage with a frequency of 50 kHz, a homogeneous discharge is generated. The radiation power density on the lamp surface is 250 W / m. At this frequency of 50 kHz and at a voltage with maximum power coupling, a stratification efficiency of more than 10% is achieved. The power and the radiation efficiency can be increased by approx. 50% by using a finer mesh structure, e.g. with 90% transmission.

Another embodiment of a lamp according to the invention has a discharge length d of 10 mm and a gas filling of 0.25 bar xenon as excimer and 0.75 bar neon as a buffer gas. Here the limit value Pg a maximum value P _M of 0.3 bar at a frequency f _M of 3.5 kHz.

The lamp is operated at a frequency of 2.5 kHz, i.e. close to the operating point (P _M , f _M ). The lamp has a radiant power density on the lamp surface of 50 W / m and a radiant efficiency of 20%.

The lighting system can be used as a flat spotlight for contact lithography or coating techniques. The lamp can also have an inner phosphor coating and can then be used for other lighting purposes, for example for backlighting of LCDs or display elements, or for general lighting.

Claims (8)

1. A lighting system which comprises a high-pressure glow discharge lamp with a planar discharge vessel which is sealed in a vacuumtight manner and which encloses a discharge space containing a gas filling which forms excimers, the parallel walls of said discharge space being formed by a dielectric material and the surfaces of the walls remote from the discharge space being provided with planar electrodes, while at least one of said walls with the associated electrode is at least partly transparent to the radiation generated, the surfaces of said walls facing the discharge space are arranged with a mutual interspacing d, and the gas filling comprises one of the rare gases Xe and Kr as the excimer former, the excimer former having a partial pressure P which is smaller than a limit value Pg, in which lighting system the lamp is fed with an AC-voltage with an operating frequency f in the operational state, characterized in that the limit value Pg is smaller in proportion as the operating frequency f differs more from a frequency f_M for which the limit value has a maximum P_M, where P_M = A+B*exp(C*d) and f_M = D*d^E, where it holds for xenon that A = 0.3 bar, B = 6 bar, and C = -1.3 mm⁻¹, with

   D = 200 kHz and E = -1.47 for d ≤2.75 mm, and

   D = 350 kHz and E = -2 for d > 2.75 mm,

   and where it holds for krypton that A = 0.75 bar, B = 150 bar, and C = -2.3 mm⁻¹, with

   D = 160 kHz and E = -1.74.
2. The use of a lighting system as claimed in Claim 1, characterized in that the lamp is operated close to the operating point (P_M, f_M).
3. A lighting system as claimed in Claim 1, characterized in that the gas filling comprises electronegative gases with a partial pressure P_D of between 5 x 10⁻⁵ 5 and 5 x 10⁻⁴ times the partial pressure of the excimer former.
4. A lighting system as claimed in Claim 1 or 3, characterized in that the gas filling in addition comprises at least one of the rare gases He, Ne, Ar, and Kr as a buffer gas when Xe is used as the excimer former, and at least one of the rare gases He, Ne, and Ar when Kr is used as the excimer former.
5. A lighting system as claimed in Claim 4, characterized in that the total pressure Pges of the gas filling is smaller than four times the partial pressure P of the excimer former.
6. A lighting system as claimed in any one of the Claims 1 and 3 to 5, characterized in that the discharge vessel has an inner layer of fluorescent material.
7. A lighting system as claimed in any one of the Claims 1 and 3 to 6, characterized in that the discharge vessel has fluorescent vessel walls.
8. A high-pressure glow discharge lamp for use in a lighting system as claimed in any one of the Claims 1 to 7, having the lamp characteristics as defined in any one of the Claims 1 and 3 to 7.

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