This is a continuous application of International Application No. PCT/JP2004/012283, filed Aug. 26, 2004.
The present invention relates to a light source device comprising a bulb, a discharge medium mainly composed to a rare gas sealed inside the bulb, and an electrode for exciting the discharge medium. The present invention also relates to a lighting device, such as a back light device, comprising this light source device, and a liquid crystal device comprising this back light device.
Recently, a research on a light source device that does not use mercury (hereafter referred to as mercury-less type) as a lamp or light source device used for a back light device of a liquid crystal display device is actively progressing, in addition to a research on a light source device using mercury for such usage. The mercury-less type light source device is preferable due to low fluctuation of light emission intensity along with time variation of temperature and in view of consideration of environments.
A known mercury-less light source device has a tubular bulb in which a rare gas is sealed, an internal electrode disposed inside the bulb, and an external electrode disposed outside the bulb. Application of a voltage between the internal electrode and external electrode causes a dielectric barrier discharge, resulting in that the rare gas is converted into plasma to emit light.
Various types of external electrodes are known. For example, a conventional light source device shown in
An external electrode, in which a conductive element is mechanically pressed to an outer face of a bulb, is also known. For example, one of conventional light source devices has an external electrode made of a conductive wire member and wound spirally around a bulb so as to closely contact with an outer surface of the bulb (for example, see Japanese Patent Application Laid-Open Publication No. 10-112290). Further, other one of conventional light source devices has an external electrode made of a conductive wire member and wound in a coil manner around an outer face of a bulb, and a shrink tube that secures the external electrode so as to be closely contact with the outer surface of the bulb (for example, see Japanese Patent Application Laid-Open Publication No. 2001-325919).
Even if the external electrode 2 is formed by coating with metal paste, the external electrode 2 cannot be completely contacted to the outer face of the bulb 3. In other words, as shown in
Even if mechanically pressed onto the outer surface of the bulb, the conductive element is detached from the outer surface of the bulb by deflection of the conductive element. Even if such a means as the shrink tube is used, it is impossible to completely contact the conductive member to the outer surface of the bulb. Therefore, the above-mentioned gap exists between the external electrode and the outer face of the bulb without exception, causing unstable light emission and dielectric breakdown of the atmospheric gas.
As discussed above, even in the case of the external electrode formed by a chemical method, such as metal paste, deposition, sputtering and adhesive, rather than such a physical method as mechanical pressing and the shrink tube, the gap between the external electrode and the outer surface of the bulb inevitably exists. The gap causes the unstable emission and the dielectric breakdown of the atmospheric gas.
It is an object of the present invention to solve the problems caused by the gap inevitably generated between the external electrode and the outer face of the bulb, and provide a highly reliable light source device that has a stable light emission characteristic and can reliably prevent dielectric breakdown of the atmospheric gas.
A first aspect of the present invention provides a light source device comprising at least one bulb, a discharge medium containing a rare gas and sealed inside the bulb, a first electrode disposed inside the bulb (internal electrode), a second electrode disposed outside the bulb (external electrode), and a holder for holding the second electrode so that the second electrode is opposed to the bulb with a predetermined distance of a space. Specifically the light source device further comprises a lighting circuit to which the first electrode is electrically connected, and the second electrode is grounded.
The second electrode disposed outside the bulb is opposed to the bulb with the predetermined distance of the space by the holder. In other words, the space is intentionally created between the bulb and the second electrode. The presence of the space achieves stable light emission of the light source device and prevents dielectric breakdown of the atmospheric gas, resulting in that highly reliable light source device can be implemented. The gas molecules of the atmospheric gas ionized by the dielectric breakdown cause damages on peripheral members. For example, if the atmospheric gas is air, the dielectric breakdown generates ozone that causes damages on the peripheral elements. According to the present invention, by preventing the dielectric breakdown of the atmospheric gas, such ionization of the gas molecules of the atmospheric gas can be prevented.
A void is created between the bulb and the second electrode by the supporter, so any shape of bulb can be used. The space between the bulb and the second electrode by the holder allows any shape of the bulb. Further, since the second electrode does not closely contact the bulb, the shape and structure of the second electrode can be simplified. These features achieves that the light source device is inexpensive and easy to manufacture.
To prevent the dielectric breakdown of the atmospheric gas with reliability, it is preferable that the distance between the second electrode and the bulb is longer than the shortest distance defined by the following equation.
For example, if the gas filled in the space is air (which has a dielectric constant of 1), then it is preferable that the distance between the second electrode and the bulb is set to a range between 0.1 mm and 2.0 mm.
A lower limit of the distance, i.e. 0.1 mm, is obtained based on the above equation. An upper limit of the distance, i.e. 2.0 mm, on the other hand, is determined according to a condition where the light source device can be lit by a reasonable input power. In other words, if the distance is excessively long, the input power for lighting the light source device should also be set excessively high, which is not practical.
An example of the rare gas to be contained in the discharge medium is xenon. Other gases, such as krypton, argon and helium, may be applied. The discharge medium may contain a plurality of types of these rare gases.
The discharge medium may contain mercury in addition to the rare gas.
If the bulb has an elongated shape which extends along an axis line thereof, it is preferable that the cross-section of the second electrode perpendicular to the axis line has a shape surrounding the bulb except for an open section.
It is also preferable that a reflection layer is formed on a surface of the second electrode so as to be opposed to the bulb.
Since the second electrode is disposed with the space from the bulb, the electrode is not provided on an outer surface of the bulb. Therefore, the reflection layer formed on the second electrode significantly reduces a ration of the light reflected by the second electrode to return the inside of the bulb with respect to the light radiated from the bulb. As a result, a total luminous flux of the light radiated from the light source device, i.e. an efficiency of the light source device, can be improved.
Further, it is unnecessary to dispose a separate reflection member to direct the light radiated from the bulb to a predetermined direction. In other words, the second electrode also functions as the reflection element. Therefore the structure of the light source device can be simplified.
The reflection layer may be a layer of material with high reflectance formed on the surface of the second electrode, or the surface of the second electrode itself with high reflectance.
If the cross-section of the bulb perpendicular to the axis line has a circular shape, it is preferable that the cross-section of the second electrode perpendicular to the axis line of the bulb has a shape except for a concentric circle with respect to the cross-section of the bulb.
For example, the cross-section of the second electrode perpendicular to the axis line of the bulb comprises a pair of first flat walls opposed to each other with the bulb therebetween, and a second flat wall which links the pair of first flat walls and is opposed to the open section with the bulb therebetween. The cross-sectional shape of the second electrode may have other shapes, such as an arc, pentagon and triangle.
Alternatively, the bulb has a shape extending along the axis line thereof, and the second electrode has a strip-like shape extending along the axis line of the bulb.
Alternatively, the bulb has a shape extending along the axis line thereof, and plural second electrodes are disposed at intervals along the axis line.
A double tube structure may be applied. In other words, the light source device may further comprise a vessel in which the bulb is enclosed, and the second electrode is formed on an inner face of the vessel. This arrangement allows that a gas other than air, such as rare gas, is filled in the space between the bulb and second electrode.
The light source device may comprise a plurality of the bulbs. In this arrangement, at least one unit of the first electrode is provided for each of the bulbs, and one unit of the second electrode is provided in common for the plurality of bulbs.
A second aspect of the present invention provides a light source device, comprising at least one bulb, a discharge medium containing rare gas and sealed inside the bulb, a first electrode disposed outside the bulb, a second electrode disposed outside the bulb, and a holder for holding the first and second electrodes so that the first and second electrodes are opposed to the vessel with a predetermined distance of space. Specifically, the light source device further comprises a lighting circuit to which the first electrode is electrically connected with the second electrode being grounded.
A third aspect of the present invention provides a lighting device, comprising the above-mentioned light source device, and a light guide plate for guiding light emitted by the light source device from a light incident surface to a light emitting surface and emitting the light from the light emitting surface. A fourth aspect of the present invention provides a liquid crystal display device comprising the above mentioned lighting device, and a liquid crystal panel disposed so as to be opposed to the light emitting surface of the light guide plate.
According to the light source device of the present invention, since the second electrode disposed outside the bulb is opposed to the bulb with the predetermined distance of the space by the holder, the light emission is stabilized, and dielectric breakdown of the atmospheric gas can be prevented. Further, the light source device is inexpensive, and can be easily manufactured.
Other objects and characteristics of the present invention shall be clarified by the following description on the preferred embodiments with reference to the accompanying drawings.
Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
As described with reference to
According to the definition of a capacitor, the capacitances C1 and C2 of capacitors 11 and 12 are respectively given by following equation (1).
In the equation (1), “S” denotes an area of the external electrode 2 covering the bulb 3, “ε1” denotes a dielectric constant of the gap 7, “ε2” denotes a dielectric constant of the solid dielectric layer 8, “X1” denotes a distance of the gap 7, and “X2” denotes a thickness of the solid dielectric layer 8.
Since the capacitors 11 and 12 are connected in series, a combined capacitance C0 is given by following equation (2).
By applying the equation (1) to the equation (2), following equation (3) is acquired.
If air is filled in the gap 7, “ε1” equals 1, following expression (3)′ is established.
Generally, a relationship indicated by following equation (4) is established among an electric charge Q, a capacitance C and a voltage V.
Q=CV (4)
If the distance X1 of the gap 7 (layer of air) increases, the combined capacitance C0 decreases, as understood by the equation (3)′. If the combined capacitance C0 decreases, the electric charge Q decreases, as understood by the equation (4). The decreasing of the electric charge Q means a decrease of the electric charge of the dielectric layer, i.e. the solid dielectric layer 8 and the void 7. This means that energy to contribute to light emission decreases, in other words, a luminous efficiency is reduced.
As discussed above, the increase of the distance X1 of the gap 7 results in the reduction of the luminous efficiency. Therefore, for those who skilled in the art, the idea of increasing the distance X1 of the void 7, that is intentionally creating the gap 7 between the external electrode 2 and the bulb 3, is entirely beyond their assumption. In other words, according to the general idea of those who skilled in the art, the external electrode 2 should closely contact to the bulb 3 as much as possible so that the generation of the gap 7 is prevented.
FIGS. 1 to 6 show a lamp or light source device 21 according to a first embodiment of the present invention. The light source device 21 comprises a air tight vessel or bulb 23 of which an inside functions as a discharge space 22, a discharge medium (not shown) sealed inside the bulb 23, an internal electrode (first electrode) 24, and an external electrode (second electrode) 25. The light source device 21 further comprises two holder members 27 for holding the external electrode 25 so that the external electrode 25 is opposed to the bulb 23 with a predetermined distance X1 of a space 26 therebetween. The light source device 21 further comprises a lighting circuit 31 for applying high frequency voltage to the discharge medium.
The bulb 23 has an elongated straight tubular shape extending along an axis line L thereof. As shown in
The bulb 23 is essentially made of material with transparency, such as borosilicate glass. The bulb 23 may be made of such glass as quartz glass, soda glass and lead glass, or organic matter such as acrylic. The outer diameter of the glass tube used for the bulb 23 is normally about 1.0 mm to 10 mm, but is not limited to these sizes. For example, the bulb 23 may be approximately 30 mm, which is common as a size of a fluorescent lamp for general-purpose illumination. The distance between an outer surface and an inner face of the glass tube, i.e. a thickness of the glass tube, is approximately 0.1 mm to 1.0 mm.
The bulb 23 is sealed, in which the discharge medium (not illustrated) is sealed. The discharge medium is one or more types of gas, mainly rare gas, but may contain mercury. The gas includes xenon, for example. Other rare gases, such as krypton, argon and helium, can be adopted. The discharge medium may contain a plurality of types of these rare gases. A pressure of the discharge medium sealed inside the bulb 23, i.e. an internal pressure of the bulb 23, is approximately 0.1 kPa to 76 kPa.
As shown in
The internal electrode 24 is disposed at one end inside the bulb 23. The internal electrode 24 is comprised of such metal as tungsten or nickel. A surface of the internal electrode 24 may be partially or entirely covered by such a metal oxide layer as cesium oxide, barium oxide or strontium oxide. By using such a metal oxide layer, a lighting start voltage can be decreased, and deterioration of the internal electrode by ion impact can be prevented. The surface of the internal electrode 24 may be covered by a dielectric layer (e.g. glass layer). A conductive member 29 has a distal end to which the internal electrode 24 is provide and a proximal end disposed outside the bulb 23. The conductive member 29 is electrically connected to the lighting circuit 31 via lead wires 30.
The external electrode 25 is comprised of conductive material such as metal including copper, aluminum and stainless. Further, the external electrode 25 is ground. As described later in detail, the external electrode 25 may be a transparent conductor of which main component is tin oxide and indium oxide. In the present embodiment, the external electrode 25 has an elongated shape extending along a direction of the axis line L of the bulb 23. As most clearly shown in
As shown in
In the light source device 21, a dielectric barrier discharge is generated between the internal electrode 24 and the external electrode 25 by applying an internal voltage using the lighting circuit 31, resulting in that the discharge medium is excited. The excited discharge medium emits ultraviolet light when moving back to the ground state. The ultraviolet light is transformed to visible light by the fluorescent layer 13, and then the visible light is emitted from the bulb 23.
Then, a supporting structure of the external electrode 25 to the bulb 23 will be described. As described above, the external electrode 25 is secured to the bulb 23 by the two holder members 27. The holder member 27 is made of a material with insulation and elasticity, such as silicon rubber. As shown in
As most clearly shown in
In the present embodiment, the distances X′1, X′2 and X′3 between the wall sections 32 to 34 of the external electrode 25 and the outer surface of the bulb 23 are respectively constant in the direction of the axis line L. Further, the distances X′1, X′2 and X′3 are the same as one another. However, the distance between the external electrode 25 and the bulb 23 need not be constant in the direction of the axis line L as long as the distance is within a range between later mentioned shortest distance and longest distance. Further, the distance between the external electrode 25 and the bulb 23 in the circumferential direction of the bulb 23 as well need not be constant.
As described above, the gap between the external electrode and the bulb is inevitably generated even if it is tried to contact the external electrode to the bulb by the physical method or the chemical method. Further, the gap destabilizes the light emission intensity and causes the dielectric breakdown of the atmospheric gas. Contrary to this, the present invention completely departures from the conventional technical common knowledge owned by those who skilled in the art, which is that the external electrode must contact the bulb as closely as possible. That is, according to the present invention, the space 26 is intentionally provided between the external electrode 25 and the outer surface of the bulb 23 in order to intentionally separate the external electrode 25 and the bulb 23 from each other. Therefore even if the spatial relationship between the external electrode 25 and the bulb 23 is slightly changed, this shift has only small influence on the distances, X′1, X′2 and X′3 of the space 26 between the external electrode 25 and the bulb 23. In other words, even if the spatial relationship between the external electrode 25 and the bulb 23 is slightly changed, the external electrode 25 can maintain the status of being separated from the bulb 23. This results in stable power supply to the bulb 23, which achieves remarkably stable emission intensity. Further, as described latter, by appropriately setting the distances X′1 to X′3 of the space 26, it can be prevented that an excessive voltage is applied to the space 26 and that the dielectric breakdown of the atmospheric gas (air in the present embodiment) filled in the space 26 occurs.
Then, quantitative settings of the distances X′1, X′2 and X′3 of the space 26 between the external electrode 25 and the bulb 23 will be described in detail. In the following description, the distances X′1, X′2 and X′3 between the outer surface of the bulb 32 and each of wall sections 32 to 34 of the external electrode 25 are collectively referred to as a “distance X1 of the space 26″.
Referring again to
Regarding the electric charge Q stored in the capacitors 41 and 42, following equation (5) is established.
Q=C0·V=C1·V1=C2·V2 (5)
In this equation, “C1” and “C2” denote capacitances of the capacitors 41 and 42, “C0” denotes combined capacitance of the capacitors 41 and 42, “V1” denotes a voltage applied to the space 26, “V2” denotes a voltage applied to the solid dielectric layer 40, and “V” denotes a voltage applied between the discharge space 22 and the external electrode 25.
The voltage V1 applied to the space 26, the voltage V2 applied to the solid dielectric layer 40, the voltage V applied between the discharge space 22 and the external electrode 25, the electric field E of the space 26, and the electric field E′ of the solid dielectric layer 40 have relationships defined by following equations (6) to (8).
V=V1+V2 (6)
From the equations (5) to (7), following equation (9) is obtained.
By applying the afore-mentioned equation (1) to the equation. (9), following equation (10) regarding the electric field E of the space 26 is obtained.
In the present embodiment, since air that has the dielectric constant of 1 is filled in the space 26, following equation (10)′ is established.
If the dielectric breakdown electric field of the space 26 is “E0”, following equation (11) needs to be established in order to prevent the occurrence of dielectric breakdown in the space 26.
E0>E (11)
By applying the equation (10) to the equation (11), following inequality (12) is obtained.
If the space 26 is filled with air (ε1=1), following inequality (12)′ is established.
Therefore, in order to prevent the dielectric breakdown in the space 26, the distance X1 of the space 26 needs to be set to be longer than the shortest distance X1L defined by following equation (13).
Especially, when the air is filled in the space 26, the shortest distance X1L is defined by following equation (13)′.
The distance X1 of the space 26 set to be longer than the shortest distance X1L prevents the dielectric breakdown of the atmospheric gas filled in the space 26 and damages of the peripheral members due to gas molecules ionized by the dielectric breakdown. In the present embodiment, since the atmospheric gas is air, it is prevented that ozone generated by the dielectric breakdown cause damages on the peripheral members.
1 The longest distance of the distance X1 of the space 26 can be determined according to a condition where the light source device can be lit by reasonable input power. In other words, if the distance is excessively long, the input power in order to activate the light source device should be set excessively high, which is unpractical.
2 If the atmospheric gas filled in the space 26 is air (which has the dielectric constant of 1) as in the present embodiment, it is preferable that the distance X1 of the space 26 is set to be not less than 0.1 mm and not more than 2.0 mm. The lower limit (0.1 mm) of the distance X1 is determined by equations (13) and (13)′. For the upper limit of the distance X1, the maximum voltage between the internal electrode 24 and the external electrode 25 is approximately 5 kV, and the distance X1 of the space 26 should be set to approximately 2.0 mm at maximum in order that the voltage of approximately 5 kV generates the discharge in the bulb 23.
Then, luminous efficiency will be described. As described with reference to equations (1) to (4), the distance X1 of the space 26 set to long, that is disposing the external electrode 25 away from the bulb 23, causes decrease in the luminous efficiency. In the present embodiment, however, an area S of the external electrode 25 that covers the bulb 23 is set to large so as to compensate for the decrease in the luminous efficiency due to existence of the space 26, and to achieve high luminous efficiency. Specifically, as understood by the equations (3) and (3)′, increasing the area S of the external electrode 25 increases the combined capacitance C0, thereby the luminous efficiency improves as understood by the equation (4).
It should be noted that the space 26 arranged between the external electrode 25 and the bulb 23 makes it possible to enhance the luminous efficiency by increasing the area S of the external electrode 2. In case that the external electrode 2 is contacted to the bulb 3 as the light source device shown in
In order to increase the luminous efficiency it is preferable that an elevation angle θ (see
If the shape of the cross-section of the bulb 23 perpendicular to the axis line L has a circular shape, as in this embodiment, it is preferable for improvement of the luminous efficiency that the cross-section of the external electrode 25 perpendicular to the axis line L has a shape except for a concentric circle with respect to the cross-sectional shape of the bulb 23. The cross-sectional shape that is not the concentric circle reduces the ratio of the light which is reflected back to the bulb 23 by the external electrode 25 with respect to the total light emitted from the bulb 23, thereby improving the luminous efficiency. In the present embodiment, because having the U-like shape as described with reference to
The external electrode 25 is separated from the bulb 23 not by a solid layer such as a solid dielectric layer, but by the space 26 in which the gas (air in the present embodiment) is filled. A first reason for this arrangement is that if the external electrode is separated from the bulb by the solid layer such as the solid dielectric layer, micro-air portions such as air bubbles exist in a boundary between the solid layer and the external electrode. Similar micro-air portions also exist in a boundary between the solid layer and the bulb. These micro-air portions cause the dielectric breakdown that generates the ozone, thereby causing damages on the peripheral members.
A second reason for the arrangement is that a low-profile or small light source device with lighter weight can be achieved. As clear by the above-mentioned equation (11), it is necessary to decrease the electric field E of the space 26 for prevention of the dielectric breakdown. The spatial separation of the external electrode and the bulb by the solid layer corresponds to increase in the thickness X2 of the solid dielectric layer in the denominator at the right-hand side of the equation (10)′ indicating the electric field E of the space 26. The coefficient which the thickness X2 is multiplied by in the denominator at the right-hand side of the equation (10)′ is 1 (ε1=1). On the other hand, the coefficient which the distance X1 of the space 26 is multiplied by in the denominator at the right-hand side of the equation (10)′ is the dielectric constant ε2 of the solid dielectric layer, which is greater than 1. Therefore, in order to effectively decrease the electric field E of the space 26, it is more efficient to increase the distance X1 of the space 26 rather than to increase the thickness X2 of the solid dielectric layer. Therefore, separating the external electrode 25 from the bulb 23 by the space 26 can achieve the light source device with low-profile or small and lighter weight more effectively than providing the solid layer such as the solid dielectric layer.
Although, in the present embodiment, the reflection layer 37 is formed on the external electrode 25, the reflection layer 37 is not an essential feature. However, if mirror-finishing for visible light has been applied to the external electrode 25, the luminous efficiency may become higher 15% higher compared to the case of that diffused reflection finishing has been applied.
Owing to the space 26 provided between the bulb 23 and the external electrode 25 by the holder member 27, the light source device 21 of the present embodiment can adopt arbitrary shape of the bulb 23. Owing to that the external electrode 25 does not contact the bulb 23, the shape and the structure of the external electrode 25 can be simplified. Owing to the reflection layer 37 formed on the external electrode 25, the function as a reflection element can be provided to the external electrode 25. In other words, since a dedicated reflection element other than the external electrode 25 is unnecessary, the number of composing elements can be decreased. Therefore, the light source device 21 is simple, inexpensive, and easy to manufacture.
(Experiment)
Concerning the light source device 21 of the first embodiment, an experiment for confirming the ozone generation suppression effect (first experiment) and an experiment for confirming the luminous efficiency (second experiment) were conducted.
With reference to
Experiment conditions of the second experiment example are the same as the experiment conditions of the first experiment example, except that the outer diameter OD of the bulb 23 is 3.0 mm, the inner diameter ID is 2.0 mm, the length of the bulb 23 and the external electrode 25 is 210 mm, and the distances X′1, X′2 and X′3 are 0.3 mm.
For both the first and second experiments, it was confirmed that the ozone is hardly generated when the distance X′3 increases to approximately 0.1 mm (100 μm).
By substituting the numeric values corresponding to the first and second experiment examples for the equation (13)′, the shortest distance X1L was calculated. As a result, the shortest distance X1L of the first experiment example was 0.14 mm, and the shortest distance X1L of the second experiment example was 0.10 mm. These calculation results approximately match the experiment results of the first and second experiment examples shown in
In the second experiment, total luminous flux of the light source device was measured for the above-mentioned first experiment example (the elevation angle θ is approximately 280 degrees) with changing the input voltage. As a first comparison example, a light source device shown in
Compared with the measurement result of the first comparison example, the total luminous flux in the second comparison example hardly increases, and rather tends to decrease. Therefore, it is confirmed that the external electrode formed so as to contact the outer face of the bulb 23 does not increase the luminous efficiency, even if the elevation angle θ is increased, that is even if the area of the external electrode is increased.
Compared with the measurement result of the first comparison example, the total luminous flux in the first experiment example remarkably increases. Particularly, when the input voltage is approximately 7W, the total luminous flux of the first experiment example increases approximately 1.7 times the total luminous flux in the first comparison example. Therefore, it is confirmed that when the space 26 is provided between the external electrode 25 and the bulb 23, the luminous efficiency is increased by increasing the elevation angle θ, that is by increasing the area of the external electrode.
By the experiment result of the second experiment, it is confirmed that merely increasing the area of the external electrode does not increase the luminous efficiency, and that increasing the area of the external electrode with the precondition that the space 26 is provided between the external electrode 25 and the bulb 23 can achieve the increase of the luminous efficiency.
The arrangement where the space 26 is provided between the bulb 23 and the external electrode 25 is particularly effective when the internal electrode 24 is disposed at one end inside the external electrode 25 is elongated along the axis line L of the bulb 23. The reason for the effectiveness will be described herein below.
When the internal electrode 24 is at the end inside the bulb 23, high voltage needs to be supplied to the bulb 23 in order to allow light to emit from the discharge medium between the internal electrode 24 and a part of the external electrode 25 positioned mostly away from the internal electrode 24. For example, in the case of the light source device of this embodiment, 2 kV of voltage needs to be supplied for this reason. By supplying such a high voltage, dielectric breakdown tends to occur between the bulb 23 and the external electrode 25 by the high voltage (maximum voltage) applied between the internal electrode 24 and a part of the external electrode 25 positioned most closely to the internal electrode 24. Contrary to this, when the distance between the internal electrode and the external electrode is approximately constant (e.g. in the case where both of the internal electrode and the external electrode extend in parallel to the axis line direction of the bulb), the necessary voltage for activating the light source device is approximately ⅙ of the necessary voltage for activating the light source device of the present embodiment, i.e., approximately 300 V of a relatively low voltage. Therefore, the arrangement where the internal electrode 24 is disposed at the end inside the bulb 23 and the external electrode 25 is elongated along the axis line L of the bulb 23, as the present embodiment, needs the voltage for activation equal to or more than six-times the voltage for activating the arrangement where the distance between the internal electrode and the external electrode is constant. For such high supplied voltage, the prevention of the dielectric breakdown by the space 26 provided between the bulb 23 and the external electrode 25 works more effectively to the arrangement as the present embodiment.
In the modification of
The light source device 21 according to a second embodiment of the present invention shown in
Since the other arrangements and functions of the second embodiment are the same as those of the first embodiment, the same elements are denoted by the same reference symbols, and descriptions thereof are omitted.
In a third embodiment shown in
Since the other arrangements and functions of the third embodiment are the same as those of the first embodiment, the same elements are denoted by the same reference symbols, and descriptions thereof are omitted.
In a fourth embodiment shown in
The external electrode 25 is formed on the inner surface of the external vessel 48. As clearly shown in
Since the other arrangements and functions of the fourth embodiment are the same as those of the first embodiment, the same elements are denoted by the same reference symbols, and descriptions thereof are omitted.
In the light source device 21 according to a modification of the fourth embodiment shown in
The light source device 21 according to a fifth embodiment of the present invention shown in
The light source device 21 may be provided with three or more bulbs 23. The bulbs 23 need not be in parallel with each other, and the plurality of the bulbs 23 can be freely arranged as long as each of the bulbs 23 is opposed to the common external electrode 25 with the space 26 therebetween.
If the external electrode 2 is formed so as to closely contact to the outer surface of the bulb 3 as shown in
Since the other arrangements and functions of the fifth embodiment are the same as those of the first embodiment, the same elements are denoted by the same reference symbols, and descriptions thereof are omitted.
The light source device 21 according to a sixth embodiment of the present invention shown in
Since the other arrangements and functions of the sixth embodiment are the same as those of the first embodiment, the same elements are denoted by the same reference symbols, and descriptions thereof are omitted.
The light source device 21 according to a seventh embodiment of the present invention shown in
The arrangement where plural internal electrodes 24 are disposed inside the single bulb 23 as the present embodiment stabilize the discharge occurred inside the bulb 23, even if the bulb 23 has a long elongated shape.
Since the other arrangements and functions of the seventh embodiment are the same as those of the first embodiment, the same elements are denoted by the same reference symbols, and descriptions thereof are omitted.
An eighth embodiment of the present invention shown in FIGS. 21 to 26 is an example where the present invention is applied to a liquid crystal display device. Specifically, the liquid crystal display device 51 of the present embodiment comprises a liquid crystal panel 52 shown only in
As shown in FIGS. 21 to 23, the back light device 53 comprises a case 57 including a top cover 55 and a back cover 56, which are made of metal. Accommodated in the back cover 56 so as to be layered are a light guide plate 59, light diffusing plate 60, lens plate 61 and polarizing plate 62. Each of the light source device 21A and 21B has L-like shape. One light source device 21A is disposed so as to be opposed to one end face 59a of the light guide plate 59 as well as other end face 59b which continues from the end face 59a. The other light source device 21B is disposed so as to be opposed to the end face 59c opposite to the end face 59a and the end face 59b. Lights emitted from the light source devices 21A and 21B enter the light guide plate 59 via the end faces 59a to 59c, and are emitted to a back face of the liquid crystal panel 52 from the emission face 59d of the light guide plate 59 via the light diffusing plate 60, lens plate 61, polarizing plate 62 and opening 55a formed in the top cover 55.
As shown in
The external electrode 25 has a U-like cross-sectional shape perpendicular to the axis line L of the bulb 23, which comprises a back wall section 64 at the back cover 56 side, a front wall section 65 at the top cover 55 side, and a side section 66 which links the back wall section 64 and the front wall section 65. An extended section 64a is formed at an edge of the back wall section 64, and a fold back section 65a is formed at an edge of the front wall section 65. As most clearly shown in
The structure and material of the holder member 27 are the same as those of the first embodiment (see
The external electrode 25 is electrically connected to one end of a lead wire 71 via the back cover 56, and the other end of the lead wire 71 is grounded. The proximal end side of the rod-like conductive member 29 having the internal electrode 24 at the proximal end is electrically connected to a lead wire 73 inside the connector 72. The connector 72 is attached to the external electrode 25 at the opposite end from the holder member 27, and is made of insulation material. The lead wire 73 is electrically connected to the lighting circuit not illustrated. At one edge of the back cover 56, a fixation member 74 made of insulation material is secured by screws 75. Between the fixation member 74 and the back cover 56, a terminal at a tip end of the lead wire 71 for the external electrode 25 is fixed The locking element 74 also has a function to guide the lead wire 73 at the internal electrode 24 side out of the case 57. The fixation element 74 also has a function to position the edges of each light source device 21A and 21B with respect to the case 57 by engaging the connector 72.
By disposing the external electrode 25 away from the bulb 23 with the space 26, the external electrode 25 of the back light device 53 has two functions in addition to the primary functions. First, the external electrode 25 functions as a reflection member for directing the light radiated from the bulb 23 to the end faces 59a to 59c of the light guide plate 59. In other words, it is unnecessary to dispose a dedicated reflection member in addition to the external electrode 25, resulting in that the number of elements is decreased. Secondly, the external electrode 25 has a function to position the light source devices 21A and 21B with respect to the light guide plate 59 as mentioned above.
Since the other arrangements and functions of the eighth embodiment are the same as those of the first embodiment, the same elements are denoted by the same reference symbols, and descriptions thereof are omitted.
The back light device 53 of the liquid crystal display device 51 according to a ninth embodiment shown in
Since the other arrangements and functions of the second embodiment are the same as those of the first embodiment, the same elements are denoted by the same reference symbols, and descriptions thereof are omitted.
The liquid crystal display device 51 according to the tenth embodiment of the present invention shown in
Since the other arrangements and functions of the second embodiment are the same as those of the first embodiment, the same elements are denoted by the same reference symbols, and descriptions thereof are omitted.
In the first to tenth embodiments, the electrode connected to the lighting circuit is the internal electrode 24 with the external electrode 25 being grounded. Whereas in an eleventh embodiment shown in
Specifically the light source device 21 according to the present embodiment comprises an external electrode 125 opposed to the external surface of the bulb 23 at around one end of the bulb 23 with the space 26 and electrically connected to the lighting circuit 31, and an external electrode 25 opposed to the outer surface of the bulb 23 at around the other end of the bulb 23 with the space 26 and being grounded. These external electrodes 25 and 125 are opposed to each other in the axis line L direction of the bulb 23 with a space. Further, these external electrodes 25 and 125 are held respectively to the bulb 23 by a holder member 27. The distance X1 between each of the external electrodes 25 and 125 and the outer face of the bulb 23 is set to be longer than the shortest distance X1L defined by the equation (13), resulting in that the dielectric breakdown between the external electrodes 25, 125 and the bulb 23 is prevented.
In case that the electrodes for connection both to the lighting circuit 31 and the ground are the external electrodes 25 and 125 as the present embodiment, the arrangement where both of the external electrodes 25 and 125 are disposed to the outer surface of the bulb 23 with the space is particularly effective. The reason for the effectiveness will be described herein below.
Because the starting voltage for dielectric barrier discharge between the external electrodes 25 and 125 is higher than that of the case when one is the internal electrode and the other is the external electrode, the dielectric breakdown easily occurs when the dielectric barrier discharge is started by the external electrodes 25 and 125. Therefore, the prevention of the dielectric breakdown by providing the space 26 between the bulb 23 and the external electrodes 25 and 125 is particularly effective for the arrangement as the present embodiment.
Since the other arrangements and functions of the eleventh embodiment are the same as those of the first embodiment, the same elements are denoted by the same reference symbols, and descriptions thereof are omitted.
The light source device of the present invention can be used not only for the back light device of the liquid crystal display device as the tenth embodiment, but also for various light sources such as a light source for general-purpose illuminations, an excimer lamp as a UV light source, and bactericidal lamp.
Although the present invention has been fully described in conjunction with preferred embodiments thereof with reference to the accompanying drawings, various changes and modifications are possible for those skilled in the art. Therefore, such changes and modifications should be construed as included in the present invention unless they depart from the intention and scope of the invention as defined by the appended claims.
Number | Date | Country | Kind |
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2003-306619 | Aug 2003 | JP | national |
Number | Date | Country | |
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Parent | PCT/JP04/12283 | Aug 2004 | US |
Child | 11362033 | Feb 2006 | US |