WO2006035339A1

WO2006035339A1 - Low-pressure gas discharge lamp

Info

Publication number: WO2006035339A1
Application number: PCT/IB2005/053056
Authority: WO
Inventors: Rainer Hilbig; Stefan Schwan
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Philips Electronics N. V.
Priority date: 2004-09-28
Filing date: 2005-09-19
Publication date: 2006-04-06

Abstract

The invention relates to a low-pressure gas discharge lamp, that comprises at least a gas discharge vessel (2) that contains a gas filling having a copper, indium, thallium or gallium compound selected from the group consisting of the halides, oxides, chalcogenides, hydroxides, hydrides, or the organometallic compounds, or the tin halides, or the chalcogenides of the main group 4 of the periodic table, or mixtures thereof, and that contains a buffer gas, and components for producing and maintaining a low-pressure gas discharge (3), the gas discharge vessel (2) having at least one region that serves primarily as an exit opening (4) for the molecular radiation of a predetermined wavelength range and a predetermined radiation density that is emitted, which radiation density, when the lamp (1) is operating, is increased in comparison with the radiation density at the other regions of the gas discharge vessel (2) at which radiation can, in principle, emerge.

Description

Low-pressure gas discharge lamp

The invention relates to a low-pressure gas discharge lamp that comprises at least a gas-discharge vessel containing a gas filling, and components for producing and maintaining a low-pressure gas discharge.

In the generation of light by low-pressure gas discharge lamps, charge carriers, which are particularly electrons but may also be ions, are accelerated in the gas discharge vessel, by an electrical field between the electrodes of the lamp, in such a way that they collide with the gas atoms or molecules in the gas filling. These collisions excite the gas filling and ionize it. When the atoms or molecules return to their ground state, atomic or molecular radiation is emitted. The generation of light in conventional low-pressure gas discharge lamps, i.e. particularly in lamps that contain mercury in the gas filling, is accomplished essentially by means of atomic radiation.

In these lamps, the reabsorption of the resonance radiation that is emitted limits the increase in the radiation density of the atomic radiation. For the purposes of the invention, radiation density is a measure of the value of the intensity of the radiation in a wavelength range, which range may be situated both in the region of the wavelength spectrum that is visible to the human eye and in the one that is not.

Low-pressure gas discharge lamps have also been described in which it is particularly molecular radiation that is emitted, such for example as in EP 1 187 173 A2 or EP l 187 174 A2.

The low-pressure gas discharge lamp that is described in EP 1 187 173 A2 is fitted with a gas discharge vessel that contains a copper-containing gas filling and a buffer gas, and with components for producing and maintaining a low-pressure gas discharge. With a construction that is comparable to that in the above-mentioned publication, there is disclosed in EP 1 187 174 A2 a low-pressure gas discharge lamp that is fitted with a gas discharge vessel that contains an indium-containing gas filling and a buffer gas. For certain applications of low-pressure gas discharge lamps, higher radiation densities are required for the molecular radiation that is emitted.

With given lamp geometries, such as for example in the case of a lamp having a cylindrical gas discharge vessel and a given lamp filling, the only way of increasing the radiation density is by increasing the power to the lamp.

It is an object of the invention to provide a low-pressure gas discharge lamp that, in a preset geometry, makes possible an increased radiation density for the molecular radiation emitted, without any increase in the power to the lamp. The object of the invention is achieved by a low-pressure gas discharge lamp having the features claimed in claim 1.

The low-pressure gas discharge lamp according to the invention comprises at least a gas discharge vessel that contains a gas filling having a copper, indium, thallium or gallium compound selected from the group consisting of the halides, oxides, chalcogenides, hydroxides, hydrides, or the organometallic compounds, or the tin halides, or the chalcogenides of the main group 4 of the periodic table, or mixtures thereof, and that contains a buffer gas, and components for producing and maintaining a low-pressure gas discharge, the gas discharge vessel having at least one region that serves primarily as an exit opening for the molecular radiation of a predetermined wavelength range and a predetermined radiation density that is emitted, which radiation density, when the lamp is operating, is increased in comparison with the radiation density at the other regions of the discharge vessel at which radiation can, in principle, emerge.

The solution according to the invention is independent of the mode of operation of the lamp in which the latter is excited to produce the gas discharge and is operated. Basically, lamps according to the invention can thus be excited and operated by means of internal or external lamp electrodes or entirely without electrodes.

When the lamp is operated by external electrodes (electrical field is coupled in), it is generally operated by means of capacitive coupling; the possibilities when there are no electrodes are, in particular, inductive operation (coupling of the magnetic field) or microwave operation (coupling of the electromagnetic field).

Components for producing and maintaining within the meaning of the invention are components that are known for applications and modes of operation of this kind, such as internal and external electrodes. These components may in turn comprise a plurality of components or parts.

The lamp according to the invention may be used in particular for tanning purposes and for treating acne, using in particular the directly emitted UV radiation for this, and for general lighting applications, particularly if the radiation from the molecules is in the visible range of the spectrum. Other preferred fields of application are as an aperture lamp (with or without phosphors), particularly for general lighting applications, and as a lamp in devices for office automation (OA), e.g. copying machines and color scanners, or for the background lighting of displays, e.g. liquid crystal displays.

There are no limitations with regard to the shape of the aperture, which is preferably in the form of a rectangular slot. Shapes such as, for example, wavy lines or letters come within the scope of the invention.

In accordance with the invention, advantage is taken of an effect in physics that, surprisingly, could be detected in measurements of radiation density made on a low- pressure gas discharge lamp of a design as described in EP 1 187 174 A2. In the test set-up, this low-pressure gas discharge lamp had, in particular, a gas discharge vessel of quartz glass that was of cylindrical geometry and had a diameter of approximately 25 mm and a length of approximately 250 mm. As well as a normal buffer gas, the gas discharge vessel also contained a gas filling having indium halides (InBr). During the test, the low-pressure gas discharge lamp was operated in a normal way by means of capacitive coupling.

The actual measurements were likewise made in a normal way in this case on two different measuring set-ups.

The measurements on the first measuring set-up were made radially relative to the longitudinal axis of the gas discharge vessel, i.e. the measurements of the radiation emitted took place at right angles to the surface of the cylindrical gas discharge vessel, or in other words were what is termed side-on. In Fig. 1, this measured spectrum from the first measuring set-up, i.e. the dependence of the radiation density on the particular wavelength, is represented by the broken line. The spectrum that can be seen in Fig. 1 is characterized in particular by the excursions of the band emission of the InBr molecule between approximately 355 nm and approximately 390 nm and of the band emissions of atomic indium at approximately 451 nm, 410 nm, 326 nm and 304 nm.

The measurements on the second measuring set-up took place under similar conditions but axially in relation to the longitudinal axis of the gas discharge vessel, i.e. the measurement of the radiation emitted was made along the longitudinal axis of the cylindrical gas discharge vessel.

With respect to radiation density, significant differences became apparent with the axially measured spectrum that is represented by the solid line in Fig. 1.

There was a sharp rise (by a factor of approximately 5.5 in the example describe) in the radiation density of the InBr molecular emission, whereas the radiation density at the atomic indium lines remained almost constant.

It is clear from these measured results that, for the geometry preset in the measuring set-up, i.e. due to the lengthening of the distanced traveled through the discharge tube along its longitudinal axis, at least part of the proportions of molecular radiation that are emitted in this volume can be exploited and that the radiation density there can be increased in this way.

Such exploitation in the above-mentioned way is not possible, under the given conditions mentioned above, for the proportions of atomic radiation (in the present case, the 410 nm and 415 nm lines for example); the radiation density of these atomic lines remains almost constant.

In accordance with the invention, this unexpected, measured effect can be used to deliberately increase the radiation density with preset operating and geometrical parameters - without any increase in the power to the lamp. This is done by exploiting the molecular radiation in selected wavelength ranges for this purpose, which radiation can, if required, be increased still further by making suitable provisions (e.g. back reflection in the gas discharge. This is successfully achieved particularly in a case where the molecular radiation from the gas discharge space is emitted by only a small part of the surface of the lamp.

The increase that is possible in the radiation density as compared with the radiation density when no additional measures are taken is dependent, as well as on geometrical factors, in particularly on the form of radiating molecule used.

The radiation density S that can be achieved is generally proportional to the particle density of the radiating species and on the effective path length L_eff over which this radiation is built up through the discharge volume along the beam to the eye. As long as the self-absorption of the emitted radiation from the radiating species (from the molecules N_m0ι in this case) is small, the radiation density S is linearly dependent on the particle density N_moi and the effective path length L_efr:

S ~ N_moi * L_eff This linear relationship holds good up to particle densities N_lin_moi at which the self-absorption of the emitted molecular radiation becomes appreciable. In increase in radiation density is however still possible up to particles densities for the molecules being considered of N_max_moi ~ 30 * N_lin_moi.

In an approximately cylindrical discharge space, as for example in the case of the measuring set-up described above, there is a relationship between the particle density of the molecules in the interior of the discharge space of the lamp according to the invention that enables molecular radiation to be exploited, and the maximum path length L_A ( = x_ab_s * (2n_r + 1)) that the molecular radiation covers through the gas discharge and that is made use of. Here, x_abS is the absorption length given by the geometry of the discharge vessel and n_r is the mean number of back reflections that are obtained by additional provisions made at the discharge vessel.

Amongst other things, this makes it possible to determine the maximum molecule density at which an increase is still possible in the density of non-coherent radiation. This maximum molecule density N_max_moi at which in increase in radiation density is, in principle, still possible can be defined as a function of molecular parameters such as, amongst others, the transition probability A_ban_d of the molecule band being considered and the latter's width of emission Δλband, and as a function of geometrical factors such as, in particular, the "simple absorption length x_abS" (e.g. the radius of a cylindrical discharge vessel) and the mean number of back reflections n_r, by for example:

N — max_m m_oo_ll = 12 - π² - c - 4 ^Δ . ^λban _d ^{' FD} _m , _^oi _{1 X} ^λband ^{• A}band - ^Xabs ^' (^{2 ' n}r ^{+ l})

The parameters that have not yet been defined are: c: The speed of light

FD_moi: The effective spectral filling factor (= O.I). The above formula can be derived from studies of radiation absorbance (Beer's law) and from certain specific properties of molecule absorbance. In the formula, the reflectance of the reflecting layers is assumed to be of an idealized form, i.e. to be 100%. This formula for the maximum molecule densities is used for the purposes of the invention to give a limiting density value for the effect described (increase in the density of non-coherent radiation). The range within which the increase in radiation density is linear with the number of reflections is the density range in which the effect gives the greatest benefit and is thus preferred.

For the InBr molecule specified in embodiment 2, what is obtained for, for example, an aperture lamp having an inside radius for the discharge vessel of 1.2 cm (= x_ab_S) and a number of mean reflections of n_r = 8, is a maximum density N_max_moi of

N_maxinBr = 10¹⁶ cm^"3. [Δλband = 30 nm, λband = 375 nm, A_band = 2.5 x 10⁶ s^"1]

A simplified formula for the increase in radiation density can be given only for the range of molecule densities N_lin_m0ι that are considerably smaller than N_max_moi (N_lin_mOι = N max_moi / 30), because the linear relationship given above between radiation density and the particle density of the radiating molecules N_moi can be used. The following equation is thus suitable for densities N_moi less than N_lin_moi:

S=S₀ -n_r -R¹' where:

S: Radiation density from the lamp when steps are taken to increase the radiation density (e.g. an aperture) S₀: Radiation density from the lamp when no steps are taken to increase the radiation density n_r: Mean number of back reflections

R: Reflectivity of the reflecting layers

For givens as in embodiment 2 (InBr, n_r = 8), what is obtained with a reflectivity R = 0.965 is an increase in radiation density (S/S_o) by a factor of 6, as long as NinBr < N_lin_mo, = 3.3 x 10¹⁴ cm^"3.

The radiation density also continues to rise for densities above N_lin_moi; the relationship however is no longer linear with the number of reflections n_r, a fact of which appropriate note needs to be taken. The dependent claims relate to advantageous further embodiments of the invention.

As an alternative, the lamp according to the invention may, in principle be equipped, and then operated as well, with internal and/or external electrodes. A further alternative is for the discharge vessel to be produced from optically transparent material only at the end-faces.

The diffusely reflecting layer may also, if desired, be applied to the outside of the gas discharge vessel. A further alternative is, when the diffusely reflecting layer is applied on the inside, for the gas discharge vessel to be produced from optically transparent material only at the points where the aperture is situated.

The object of the invention is also achieved by a lighting unit having at least one low-pressure gas discharge lamp as claimed in claims 1 to 10. The lighting unit according to the invention having at least one low-pressure gas discharge lamp may be used in particular for tanning purposes and for treating acne, using in particular the directly emitted UV radiation for this, and for general lighting applications, particularly if the radiation from the molecules is in the visible range of the spectrum. Other preferred fields of application are as an aperture lamp unit with or without phosphors, particularly for general lighting applications, and as a lamp in devices for office automation (OA), e.g. copying machines and color scanners, or for the background lighting of displays, e.g. liquid crystal displays.

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.

In the drawings:

Fig. 2 is a schematic side view of a low-pressure gas discharge lamp and a measuring set-up (for head-on measurement). Fig. 3 is a schematic view in section through a cylindrical gas discharge lamp.

The present low-pressure gas discharge lamp 1 , provided with a measuring set-up (for head-on measurement) is, as can be seen in Fig. 2, arranged in an electrical heating oven 8. The measuring device 7 is arranged approximately on the longitudinal axis of the lamp 1 and is spaced away from an end-face of the lamp 1.

The low-pressure gas discharge lamp 1 has a gas discharge vessel 2 of quartz glass that is of cylindrical, tubular geometry and has a diameter of approximately 25 cm and a length of approximately 250 mm (length of lamp: L; inside diameter of lamp: d; L » d). The inside diameter of the gas discharge vessel is approximately 24 cm. In its interior, the hermetically sealed gas discharge vessel 2 contains, as well as a normal buffer gas such as argon, a gas filling containing indium halides (InBr). The low-pressure gas discharge lamp 1 is operated in a normal manner by means of capacitive coupling. The components for producing and maintaining a low-pressure gas discharge 3, which in the present case are amongst others the components of the capacitive coupling system, are arranged in particular at the two ends of the gas discharge vessel 2. Applied to the inside surface of the gas discharge vessel 2, but not at the two end-faces, is a normal diffusely reflecting coating 5, which in particular does not allow any molecular radiation to pass through. The two end- faces act as exit openings 4 for the molecular radiation that is emitted, particularly in the predetermined wavelength range from 355 nm to 390 nm. To the outer surface of the ends may be applied a normal layer of phosphor 6 that in particular causes UV radiation to be converted into visible radiation, and in this specific case into white light.

As an alternative, the lamp according to the invention may, in principle, be equipped, and then operated as well, with internal and/or external electrodes.

A further alternative is for the discharge vessel to be produced from optically transparent material only at the end-faces.

A further preferred embodiment is shown schematically in Fig. 3. What is shown is a section through a cylindrical gas discharge lamp, namely a section at the center of the tubular lamp 1. Not shown are the provisions that are made, which are shown in Fig. 1 , to bring the gas discharge vessel 2 to a temperature at its coldest point of, for example, 218⁰C. This can for example be done by a heating oven, as in the case of the first embodiment, or by an outer enclosing tube provided with conventional heat-reflecting layers.

The low-pressure gas discharge lamp 1 shown has a gas discharge vessel 2 of quartz glass that is of cylindrical, tubular geometry and has a diameter of approximately 25 cm and a length of approximately 250 mm. In its interior, the hermetically sealed gas discharge vessel 2 contains, as well as a normal buffer gas such as argon, a gas filling containing indium halides (InBr). The low-pressure gas discharge lamp 1 is operated in a normal manner by means of capacitive coupling. Except in the region that is marked as the aperture 9, there is applied to the inside surface a diffusely reflecting coating 5 that in particular does not allow molecular radiation to pass through. The aperture 9 acts as an exit opening 4 for the molecular radiation, particularly in the predetermined wavelength range from 355 nm to 390 nm, that is emitted. The diffusely reflecting layer 5 may also, if desired, be applied to the outside of the gas discharge vessel 2.

A further alternative is, when the diffusely reflecting layer 5 is applied on the inside, for the gas discharge vessel 2 to be produced from optically transparent material only at the points where the aperture 9 is situated.

In line with the calculations given above in the text, what is obtained for the InBr molecule specified in this embodiment, when the ratio of the surface area of the aperture to the total surface area of the cylinder formed by the gas discharge vessel 2 is 1/8 (number of mean reflections of n_r = 8), is a maximum density N_max_moi = N_max_moii_nBr = 10¹⁶ cm^"3. With a reflectivity R for the diffusely reflecting layer equal to or greater than R = 0.965, an increase in the intensity of the radiation by a factor of 6 is obtained as compared with a gas discharge vessel 2 not having a diffusely reflecting coating of this kind.

On for example the inside or outside of the gas discharge vessel 2, a normal phosphor layer may, in addition, be applied to the aperture 9, which layer in particular causes the UV radiation from 355 nm to 390 nm to be converted into visible radiation, and in this specific case into white light.

As an alternative, the lamp according to the invention may, in principle be equipped, and then operated as well, with internal and/or external electrodes.

Claims

CLAIMS:

1. A low-pressure gas discharge lamp, at least comprising a gas discharge vessel (2) that contains a gas filling having a copper, indium, thallium or gallium compound selected from the group consisting of the halides, oxides, chalcogenides, hydroxides, hydrides, or the organometallic compounds, or the tin halides, or the chalcogenides of the main group 4 of the periodic table, or mixtures thereof and that contains a buffer gas, and components for producing and maintaining a low-pressure gas discharge (3), the gas discharge vessel (2) having at least one region that serves primarily as an exit opening (4) for the molecular radiation of a predetermined wavelength range and a predetermined radiation density that is emitted, which radiation density, when the lamp (1) is operating, is increased in comparison with the radiation density at the other regions of the discharge vessel (2) at which radiation can, in principle, emerge.

2. A low-pressure gas discharge lamp as claimed in claim 1, characterized in that the molecule density in the gas phase of the gas filling is less than the value given by the following equation _{xτ I Λ} 2 ^Δλband "FD_moI

N_max_raol = 12V -c- λband ^{• A}band -^χabs -(² -ⁿr ^{+ 1})

3. A low-pressure gas discharge lamp as claimed in claim 1, characterized in that the gas filling comprises indium chloride or gallium chloride, indium bromide or gallium bromide, or indium iodide or gallium iodide, or mixtures thereof.

4. A low-pressure gas discharge lamp as claimed in claim 3, characterized in that the predetermined wavelength range is a range from approximately 320 to approximately 430 nm.

5. A low-pressure gas discharge lamp as claimed in claim 1, characterized in that the region of the exit opening (4) for the molecular radiation emitted is one end of the cylindrical gas discharge vessel (2).

6. A low-pressure gas discharge lamp as claimed in claim 1, characterized in that the region of the exit opening (4) for the molecular radiation emitted is an aperture (9) of the cylindrical gas discharge vessel (2).

7. A low-pressure gas discharge lamp as claimed in claim 1, characterized in that components that promote and/or increase the egress of the molecular radiation emitted in the predetermined wavelength range are arranged in and/or on the gas discharge vessel (2).

8. A low-pressure gas discharge lamp as claimed in claim 7, characterized in that the gas discharge vessel (2) has a diffusely reflecting layer (5) on part of its inner and/or outer surface.

9. A low-pressure gas discharge lamp as claimed in claim 1 , characterized in that the molecular radiation strikes a phosphor layer (6) at the exit opening (4), at the aperture (9) or after passing through the exit opening (4).

10. A low-pressure gas discharge lamp as claimed in claim 1, characterized in that the lamp (1) is excited and operated by means of internal and/or external lamp electrodes or entirely without electrodes.

11. A lighting unit having at least one low-pressure gas discharge lamp (1) as claimed in anyone of claims 1 to 10.