JP2007272041A - Lamp unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a structure which constitutes a backlight unit by using a hot cathode fluorescent lamp and can more enhance luminance efficiency as the unit. <P>SOLUTION: The backlight unit 5 is a directly under type irradiating a liquid crystal panel from its directly under part and is provided with an e.g. six hot cathode fluorescent lamps 7 to be light sources, a casing 9 housing the hot cathode fluorescent lamps 7, a lighting circuit lighting the hot cathode fluorescent lamps 7 and optical sheets 13 provided on the front surface of the casing 9. When the backlight unit 5 is viewed from the optical sheets 13 side, the hot cathode fluorescent lamps 7 is held by a part corresponding to a rear side of a peripheral region (an outer side of a line segment C in Fig.) of the optical sheets 13 and a rear surface side part of the casing 9 to be a part corresponding to a central region (inner side of a line segment D in Fig.) of the hot cathode fluorescent lamps 7 comes in contact with the casing 9 via a heat conductive member 35. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lamp unit including a hot cathode fluorescent lamp as a light source in a case.

Conventionally, there are various types of image display devices such as a television and a display (monitor). In recent years, demands for power saving, thinning of display devices and large screens have increased, and liquid crystal display devices are becoming one of the mainstream display devices.
The liquid crystal display device includes a liquid crystal panel and a backlight unit. The greater the light emitted from the backlight unit, the higher the brightness of the image displayed on the screen of the liquid crystal display device. Optical sheets are mounted on the front surface of the backlight unit (the surface on the liquid crystal panel side). By using these optical sheets, even when a uniform screen (for example, a black screen) is displayed, it is possible to obtain a high degree of uniformity without a local grayscale difference on the screen.

  As the fluorescent lamp used as the light source of the backlight unit, a cold cathode fluorescent lamp having an outer diameter of about 4 (mm) is mainly used to reduce the thickness until the screen size is about 26 type. In addition, when the screen size increases, a so-called direct type that can increase the number of fluorescent lamps stored in the housing is mainly used as the type of backlight unit (for example, Patent Documents 1 to 4).

  Among backlight units using cold-cathode fluorescent lamps, especially for ultra-large liquid crystal display devices with a screen size exceeding 26 types, the driving voltage of the lamp is increased to ensure high brightness, and measures for insulation are provided. In addition, there are problems that a complicated structure is required, and that many lamps are required to secure screen brightness as a liquid crystal display device, and that assembling as a backlight unit takes time. In order to increase the luminance per lamp, for example, it is conceivable to increase the outer diameter of the lamp. However, the driving voltage increases as the outer diameter is increased, making it difficult to put it to practical use.

Therefore, attempts have been made in recent years to construct a backlight unit for a liquid crystal display using a hot cathode fluorescent lamp whose driving voltage is theoretically smaller than that of a cold shade fluorescent lamp and having a slightly larger outer diameter.
Japanese Patent Application Laid-Open No. 07-064083 Japanese Patent Laid-Open No. 03-018721 JP 2000-010094 A JP 2006-004880 A

However, a backlight unit for a liquid crystal display device using a hot cathode fluorescent lamp has a lower driving voltage and higher luminance than those using a cold cathode fluorescent lamp, but the luminance efficiency is further improved as a backlight unit. There is a desire to want.
An object of the present invention is to provide a structure in which a lamp unit is configured using a hot cathode fluorescent lamp and the luminance efficiency can be further improved as a unit.

  In order to achieve the above object, a lamp unit according to the present invention is a lamp unit in which a hot cathode fluorescent lamp is housed in a case and emits light forward from the central region excluding the peripheral region of the front surface of the case. The hot cathode fluorescent lamp is held in a peripheral region of the front surface of the case when the case is viewed from the front side, and a portion corresponding to the central region of the hot cathode fluorescent lamp is interposed through the heat conducting member. It is characterized by being in contact with the bottom of the case.

The number of the hot cathode fluorescent lamps here may be one or more. In one hot cathode fluorescent lamp, the number of locations that contact the case via the heat conducting member may be one, or a plurality of locations.
Further, “in contact” in the present invention means that heat of the hot cathode fluorescent lamp is transmitted to the heat conducting member. For example, when a hot cathode fluorescent lamp having an outer diameter slightly larger than that of a cold cathode fluorescent lamp is used, the mechanical strength thereof is also strong. It is not always necessary to hold the portion corresponding to. Therefore, depending on the shape of the heat conducting member, the hot cathode fluorescent lamp and the heat conducting member may come in contact with each other over a wide range, but the function of holding the hot cathode fluorescent lamp with only the heat conducting member is essential to the present invention. It is not a thing.

In addition, the bottom surface of the case is a reflection surface that reflects light from the hot cathode fluorescent lamp forward.
On the other hand, the outer peripheral length in the cross section of the glass tube constituting the discharge space of the hot cathode fluorescent lamp is in the range of 47 mm or more and 95 mm or less, and the glass tube has its cross section shape Is substantially circular, and in the cross section of the glass tube, the heat conducting member is an intersection of a line segment perpendicular to the front surface of the case and passing through the center of the glass tube, and the outer periphery of the glass tube. With reference to the point located on the bottom side of the case, the glass tube is in contact with a part or all of the outer peripheral region connecting the outer peripheral positions of the glass tube displaced ± 30 degrees around the center of the glass tube. It is said.

  Furthermore, the cross-sectional shape of the said glass tube is non-circular shape, The part located in the opposite side to the said center area | region in the said glass tube is characterized by the flat shape. Alternatively, the cross-sectional shape of the glass tube is non-circular, and the diameter in the direction parallel to the bottom surface of the case is larger than the diameter in the direction perpendicular to the bottom surface. The surface shape is a substantially elliptical shape or a substantially oval shape, and the ratio of the minor axis to the major axis is 1.1 or more.

On the other hand, the heat conducting member is made of a material having a thermal conductivity of 10 W / m / K or more, or the heat conducting member is at or near the coldest spot of the hot cathode fluorescent lamp. Thus, the hot cathode fluorescent lamp and the case are thermally connected.
In the heat conducting member, an area in contact with the hot cathode fluorescent lamp is smaller than an area in contact with the bottom surface. Alternatively, the heat conducting member penetrates the bottom wall of the case and the case. Further, the heat conducting member is made of a material having a light reflectance equivalent to that of the reflecting surface, or on the surface of the heat conducting member. A material having a light reflectivity equivalent to that of the reflecting surface is coated.

  In the lamp unit according to the present invention, the hot cathode fluorescent lamp and the bottom surface of the case are brought into contact with each other via the heat conducting member, so that the heat of the hot cathode fluorescent lamp during lighting can be transmitted from the heat conducting member to the case. . Thereby, for example, when the temperature of the coldest spot of the hot cathode fluorescent lamp at the time of lighting is higher than the optimum temperature at which the luminous efficiency becomes the best, the cold spot position of the hot cathode fluorescent lamp at the time of lighting is set. The temperature approaches the temperature at which the luminous efficiency becomes the best, and the luminous efficiency of the hot cathode fluorescent lamp can be further increased. As a result, the luminance efficiency of the lamp unit can be improved.

  Further, since the heat conducting member is disposed on the back side of the portion corresponding to the central region of the case in the hot cathode fluorescent lamp, the light emitted forward from the hot cathode fluorescent lamp is not blocked, and the brightness as a lamp unit is obtained. Reduction can be reduced.

An embodiment in which the present invention is applied to a liquid crystal television which is a liquid crystal display device will be described with reference to the drawings.
<First Embodiment>
1. Configuration of Liquid Crystal Television FIG. 1 is an exploded perspective view showing a schematic configuration of a liquid crystal television 1 according to the present embodiment.

The liquid crystal television 1 includes a liquid crystal panel 3 and a backlight unit 5 (a lamp unit in the present invention) installed on the back surface of the liquid crystal panel 3.
The liquid crystal panel 3 has an effective screen size of, for example, 45 inches diagonal and an aspect ratio of 16: 9 (the ratio of the vertical length divided by the horizontal length is 9/16), and is a color filter substrate, liquid crystal, TFT A substrate or the like (not shown) is provided, and a color image is formed on the screen 3a by being driven by a drive module (not shown) based on an external image signal.

  The backlight unit 5 is a direct type that irradiates from directly below the liquid crystal panel 3, and includes a plurality of (for example, six) hot cathode fluorescent lamps (hereinafter simply referred to as “lamps”) 7 that serve as light sources, and the lamps 7. And a lighting circuit 11 for lighting the lamp 7, and an optical sheet 13 mounted on the front surface of the housing 9, and the liquid crystal panel 3 is irradiated from the back surface.

The “case” according to the present invention includes the housing 9 and the optical sheets 13 in the first embodiment, and the “front surface” according to the present invention corresponds to the optical sheets 13 in the first embodiment. It corresponds to.
2. Configuration of Backlight Unit FIG. 2 is a view of the cross section of the virtual plane X in FIG. 1 as viewed from the direction of the arrow, and FIG. 3 is a view of the backlight unit as viewed from the liquid crystal panel side (front side). The optical sheets are partly cut away so that the situation can be seen.

As shown in FIGS. 2 and 3, the housing 9 has a box shape with an opening on the liquid crystal panel 3 side, and has a rectangular bottom wall 9a and four side walls 9b erected from each side of the bottom wall 9a. , 9c, 9d, 9e, and the inner surface of the housing 9 reflects the light emitted from the lamp 7 forward, that is, toward the liquid crystal panel 3 (for example, arrows A and B in FIG. 2). ) It is a reflective surface.
The lighting circuit 11 is a power supply circuit that supplies power to the lamp 7 and has a dimming function that can arbitrarily adjust the amount of power to be supplied and adjust the luminance. The lighting circuit 11 in the backlight unit 5 here is disposed outside the housing 9 as shown in FIG. 1, but the backlight having a structure in which the lighting circuit 11 is disposed in the housing 9. A unit may be used.

The optical sheets 13 are obtained by laminating thin plates having optical functions such as a diffusion plate, a diffusion sheet, a prism sheet, and a polarizing plate, and the surface of the optical sheets 13 serves as a light emitting surface of the backlight unit 5. The optical sheets 13 are designed so that the light emitted from the light emitting surface becomes substantially uniform parallel light.
The housing 9 is made of, for example, polycarbonate (PC) resin, and the inner reflective surface is formed by vapor deposition of a metal such as silver. The material of the housing 9 and the configuration of the reflecting surface are not limited to this example, and may be composed of other materials.

  The six lamps 7 are so-called hot-cathode fluorescent lamps, and have a posture in which the axis of the lamp is parallel to the horizontal direction of the screen 3 a of the liquid crystal panel 3 (longitudinal direction of the bottom wall 9 a of the housing 9). Are stored in the housing 9 at a predetermined interval in the vertical direction of the screen 3a (the short side of the bottom wall 9a), and when the backlight unit 5 is viewed from the front side, The front surface is held at a position corresponding to the back side of the peripheral region of the optical sheet 13.

FIG. 4 is a diagram illustrating the configuration of the lamp, and a part of the lamp is cut away so that the inside can be seen.
As shown in FIG. 4, the lamp 7 is a low-pressure mercury discharge lamp, and includes a glass tube 15 and electrodes 17 and 19 sealed at each end of the glass tube 15.
The glass tube 15 is, for example, one having an outer diameter of 18 (mm), a wall thickness of 0.8 (mm), and a length of 1010 (mm), and inside thereof mercury (for example, a luminescent substance) 4 (mg) to 10 (mg)) and a mixed gas of argon and krypton (for example, a mixed gas having a ratio of Ar (50%) and Kr (50)) as a buffer gas, For example, it is sealed with a sealed gas pressure of 600 (Pa).

On the inner surface of the glass tube 15 is formed a phosphor layer 21 that converts ultraviolet rays (specifically, a wavelength of 254 (nm)) emitted from mercury into visible light. The phosphor layer 21 is, for example, a red, blue, or green three-wavelength type. For example, Y ₂ O ₃ : Eu, LaPO ₄ : Ce, Tb, and BaMg ₂ Al ₁₆ O ₂₇ : Eu, Mn fluorescence The body is used.
Since the electrode 19 has the same structure as the electrode 17, the description here will be made on the electrode 17. The electrode 17 is a hot cathode type. As shown in FIG. 4, the electrode 17 is of a so-called bead glass mount type, and includes a filament coil 23 made of tungsten, a pair of lead wires 25 and 27 for holding the filament coil 23, and a pair of It consists of a bead glass 29 for fixing and supporting the lead wires 25 and 27.

It is a part of the lead wires 25 and 27 that is sealed to the end portion of the glass tube 15 in the electrode 17 (, 19). Specifically, the electrode 17 (, 19) extends from the bead glass 29 to the opposite side of the filament coil 23. It is a part. The electrodes 17 and 19 are sealed to the glass tube 15 by, for example, pinch sealing, as can be seen from FIG.
An exhaust pipe 31 is attached together with the electrode 17 at one end of the glass tube 15 (here, the electrode 17 side). The exhaust pipe 31 is used when exhausting the inside of the glass tube 15 or sealing the buffer gas or the like after sealing the electrodes 17, 19, etc. When the sealing is completed, for example, chip-off sealing is performed at a portion of the exhaust pipe 31 located outside the glass tube 15.

As shown in FIG. 3, the lamp 7 corresponds to the back side of the front surface (optical sheet 13) peripheral region (the outer region surrounded by the line segment (solid line and broken line) C in the drawing) of the backlight unit 5. Is attached to the housing 9. The lamp 7 is fixed and supported by a known fixture 33.
As shown in FIG. 2, the surface of the lamp 7 opposite to the optical sheet 13 of the lamp 7 is thermally connected to the bottom wall 9 a of the housing 9 through a heat conducting member 35. With this configuration, the heat of the lamp 7 at the time of lighting is transmitted to the housing 9 through the heat conducting member 35, and the temperature of the lamp 7 is optimized. That is, the heat of the lamp 7 at the time of lighting is released, and the temperature of the lamp 7 is made to substantially coincide with the temperature with the highest luminous efficiency.

  The heat conducting member 35 is a material having a higher thermal conductivity than air, and as shown in the enlarged view of FIG. 2, the direction parallel to the main surface of the optical sheet 13 (in other words, the screen 3a of the liquid crystal panel 3 and It is a direction parallel to the “X” direction in the drawing) (the “Y” direction in the drawing), and a line segment passing through the axis O of the lamp 7 is defined as Y1. In the cross section of the lamp 7, to the outer peripheral position shifted by ± 30 (degrees) around the axis of the lamp 7 on the basis of the intersection of the line segment Y1 and the outer periphery of the glass tube 15 and close to the bottom wall 9a Is in contact with the lamp 7 in a part of the area (peripheral area from A to B in the figure).

3. 3. Lamp temperature 3-1. In the case of a hot cathode fluorescent lamp The mercury vapor pressure inside the lamp 7 when the lamp 7 is driven (lighted) is influenced by the lowest temperature (cold spot temperature) in the lamp 7, which increases the lamp efficiency of the lamp 7. It is known to decide.

When the coldest spot temperature at which the lamp efficiency is maximized was measured for the lamp 7 having the above configuration (the outer diameter was 18 mm), the coldest spot was about 50 ° C., and the coldest spot was the length of the lamp 7. It was approximately the center of the direction.
On the other hand, in the commercially available hot cathode fluorescent lamp having an outer diameter of 32 (mm), the coldest spot temperature at which the luminous efficiency is maximized was 45 ° C. From the above result (lamp having an outer diameter of 18 (mm)) and this result (lamp having an outer diameter of 32 (mm)), the coldest spot temperature at which the luminous efficiency of the lamp is maximized is monotonous with respect to the outer diameter of the glass tube. It seems that it tends to decrease.

When the backlight unit 5 described above was used and the lamps 7 were turned on with a lamp power of 30 (W) per lamp, the measured temperature at the coldest spot was about 60 ° C.
Therefore, when the backlight unit 5 having the above configuration is configured using the lamp 7 having the outer diameter of 18 (mm) described above, when the lamp 7 is lit with the highest luminous efficiency, It is necessary to lower the coldest spot temperature of the lamp 7 by about 10 ° C. from the current 60 ° C. to 50 ° C.

Therefore, the inventors transmit the heat at the coldest spot of the lamp 7 from the heat conducting member 35 to the housing 9 in order to lower the lamp temperature (temperature at the coldest spot) during lighting by 10 ° C. We considered heat dissipation.
3-2. Cold Cathode Fluorescent Lamp When the light source of the backlight unit for a liquid crystal television having an effective screen size of 45 inches diagonal is constituted by a cold cathode fluorescent lamp, 24 cold cathode fluorescent lamps having an outer diameter of a glass tube of 4 (mm) are used. It is necessary to light with a lamp power of 7.5 (W) per lamp. In the cold cathode fluorescent lamp, a mixed gas of 95% (%) neon and 5% (%) argon is sealed as a buffer gas at a sealed gas pressure of 8000 (Pa).

  The measured value of the temperature at the coldest spot when the cold cathode fluorescent lamp was turned on was 70 ° C. As a result, in the cold cathode fluorescent lamp having a thin outer diameter, the coldest spot temperature at which the luminous efficiency is maximized is 70 ° C., and this temperature is the coldest spot of the cold cathode fluorescent lamp in the backlight unit. This coincides with 70 ° C. which is the actually measured temperature at the location. For this reason, it can be said that a cold cathode fluorescent lamp having an outer diameter of 4 (mm) is used as a light source for a backlight unit in an efficient place.

3-3. About the coldest spot The coldest spot of the lamp does not necessarily have to be the central part in the longitudinal direction of the lamp. Functions as a cold spot.
However, in the prototype hot cathode fluorescent lamp, one end of the lamp at a position away from the central portion in the longitudinal direction of the lamp was forcibly cooled to form the coldest spot, so that the temperature became the light emission characteristic of the entire lamp. It has been found that there is a problem that it takes at least two hours to influence and reach a stable state and takes too much time.

  Therefore, in order to obtain a stable light output characteristic as a backlight unit at an early stage, the contact portion between the heat conducting member and the lamp should be the central portion in the longitudinal direction of the lamp and its peripheral portion rather than the end portion of the lamp. desirable. The central portion and the peripheral portion referred to here are between the electrode ends on both sides of the lamp. For example, in the prototyped hot cathode fluorescent lamp having a length of 1010 (mm), the central portion and the peripheral portion are respectively 40 (mm) or more from the electrode end toward the central portion. Desirable range (range 40 mm or more away from the electrode end).

4). Regarding the contact range with the heat conducting member In general, as described above, the backlight unit is required to have high luminance as the screen becomes larger. For this reason, the inventors studied to transmit the heat at the coldest spot of the lamp from the heat conducting member to the housing without causing a decrease in luminance as a backlight unit.
Specifically, the optimum contact area between the lamp and the heat conducting member was investigated.

  The content of the study is that when a backlight unit having a thickness of 24 (mm) is configured with six lamps, the point on the bottom wall 9a side is the intersection of the outer periphery of the lamp cross section and the line segment Y1. The outer periphery of the lamp cross section is divided by 30 degrees with reference to light, and the light emitted from each of the divided outer peripheral surfaces (the divided outer peripheral surfaces are also referred to as “divided regions”) The total luminous flux (this total luminous flux) emitted from the central area on the front surface of the backlight unit using a lamp that emits light from the inner side (the inner area of the periphery of the optical sheet 13, hereinafter also referred to as “backlight emitting surface”). Is also referred to as “backlight light-emitting surface light flux”)).

That is, the contribution ratio of the light beam emitted from each divided region of the lamp to the backlight light-emitting surface light beam was obtained by calculation. The calculation is carried out using a model in which light is not emitted over the entire length of the lamp other than the divided areas to be calculated in the lamp cross section.
FIG. 5 is a diagram showing a contribution ratio of the light from the divided regions of the lamp to the backlight light-emitting surface light flux.

In the cross section of the lamp, the outer periphery of the lamp is divided into a total of six regions of 30 degrees each on both sides symmetrical to each other across the line segment Y1 in FIG. The side close to the bottom wall 9a is the “lower” side, and the side close to the optical sheets 13 is the “upper” side.
In FIG. 5, for example, “down 0-30 degrees” is an intersection of the line segment Y1 and the outer periphery of the lamp and is close to the bottom wall 9a of the housing 9, and is based on the line segment Y1 (that is, at 0 degrees). As shown in FIG. 5, the area up to 30 degrees on both sides of the line segment Y1, that is, the area where “θ” in FIG. 5 is from 0 degrees to 30 degrees is shown.

From FIG. 5, the contribution ratio of each divided region is highest in “up 0-30 degrees”, “up 30-60 degrees”, “up 60-90 degrees”, “down 60-90 degrees”, “bottom 30”. It decreases in the order of “−60 degrees” and “below 0-30 degrees”.
That is, the contribution ratio of the luminous flux emitted from the “lower 0-30 degree” divided area, that is, the area facing the bottom wall 9a of the housing 9 to the backlight emission surface luminous flux is emitted from the other divided areas. The contribution ratio of “lower 0-30 degrees” is much lower than the contribution ratio of “lower 30-60 degrees” located next to it.

From the above, when the lamp is divided into six in the circumferential direction, even if light does not exit from the “lower 0-30 degrees” divided region, the decrease in the luminous flux of the backlight emitting surface is small, and the backlight emitting surface It can be seen that the luminance can be maintained at 85 (%) with respect to the luminance when light is emitted from the entire surface of the lamp.
The inventors consider the contribution ratio to the light emission surface light flux of the backlight in the “lower 0-30 degree” divided region, and if a part or all of this divided region is brought into contact with the heat conducting member, It has been found that the lamp temperature during lighting can be lowered with little decrease in luminance of the light emitting surface.

Then, by connecting the lamp to the housing via the heat conducting member, the coldest spot temperature of the lamp at the time of lighting can be lowered, and the temperature of the lamp at the time of lighting is optimal so that high luminous efficiency can be obtained. Since the temperature can be matched with or close to the temperature, as a result, the luminous efficiency of the lamp can be improved by about 10% at the maximum.
In this study, it has been described that the luminance of the backlight emitting surface is reduced to 85 (%) when only the divided region of “0-30 degrees below” is a region that does not emit light. This is the result when the total length of the lamp is 1010 (mm) and no light is emitted over the entire “lower 0-30 degrees” region. The total length of the backlight is determined by the material, but if it is, for example, 10 (mm), the luminance of the backlight light-emitting surface is secured to about 99 (%).

Therefore, if the luminous efficiency is improved by about 10% by lowering the lamp temperature at the time of lighting, even if the luminance is reduced by about 1% due to the influence of the heat conduction member, the luminous efficiency is improved as a result. In addition, the luminance of the backlight emission surface can be improved.
5). About luminance unevenness Since the backlight unit is used as a light source of a liquid crystal panel, it is required that the backlight unit has a uniform luminance without uneven luminance on the light emitting surface of the backlight. However, depending on the location where the heat conducting member is provided as described above, the luminous flux is locally lowered to form a dark portion on the backlight light emitting surface, thereby causing uneven brightness. For this reason, the inventors studied to transmit the heat at the coldest spot of the lamp from the heat conducting member to the housing without increasing the luminance unevenness of the backlight emission surface.

As a result of investigating the contribution ratio of the luminous flux from the above-mentioned divided area of the lamp to the backlight luminous surface luminous flux, the inventors have found that the above-mentioned "lower 0-30 degree" divided area contributes to the backlight luminous luminous flux. Since the contribution rate is low, it has been found that if a heat conduction member is provided in this divided region, the luminance unevenness on the backlight emission surface can be reduced.
<Second Embodiment>
In the first embodiment, the cross-sectional shape of the glass tube 15 of the lamp 7 is circular, but other shapes may be used. In the second embodiment, a backlight unit using a lamp whose glass tube has an elliptical cross-sectional shape will be described.

1. Configuration of Backlight Unit FIG. 6 is a view of a cross section when the backlight unit according to the second embodiment is cut along a virtual plane corresponding to the virtual plane X of FIG.
As shown in FIG. 6, the backlight unit 101 according to the second embodiment includes a plurality of, for example, six lamps 103 inside the housing 105, and the front surface of the housing 105 (the surface on the liquid crystal panel side). The optical sheet 107 similar to that of the first embodiment is mounted in the opening of ().

  As shown in the enlarged view of FIG. 6, the lamp 103 has an elliptical shape in which the cross-sectional shape is, for example, a major axis of 21 (mm) and a minor axis of 15 (mm), and the major axis of the elliptical shape is an optical sheet. A central portion in the longitudinal direction of the lamp that is the coldest spot of the lamp 103 or the central portion of the lamp 103 as in the first embodiment. The side opposite to the side where the optical sheet 107 is located is in contact with the heat conducting member 109 provided on the bottom wall 105 a of the housing 105.

  As shown in the enlarged view of FIG. 6, the heat conducting member 109 according to the second embodiment includes a contact portion 109 a that contacts the outer peripheral surface of the lamp 103 inside the housing 105, and the housing 105. A heat dissipating portion 109b that is located outside and dissipates heat from the lamp 103 to the outside of the housing 105, and a through hole 105b in the bottom wall 105a of the housing 105 are inserted to connect the contact portion 109a and the heat dissipating portion 109b. Connecting portion 109c.

By configuring the heat conducting member 109 as shown in the second embodiment, the heat from the lamp 103 can be conducted to the outside of the housing 105, and the heat dissipation can be further improved.
Here, the heat-conducting member 109 includes the abutting portion 109a, the connecting portion 109c, and the heat-dissipating portion 109b, and is obtained by machining a block of polycarbonate, for example. It may be. Further, the lamp 103 is different from the first embodiment only in the cross-sectional shape of the glass tube, and other configurations, for example, the configuration of the phosphor layer, the electrode, and the like are the same as those in the first embodiment. .

2. Lamp posture 2-1. Regarding the luminance distribution The inventors made a prototype of a lamp 103 having a minor axis of 15 (mm), a major axis of 21 (mm), and a length of 1010 (mm), and changing the posture (orientation) of the lamp 103. The light unit 101 (including the optical sheet) was actually manufactured to measure the luminance distribution of the backlight emission surface, and the luminance distribution of the backlight emission surface by simulation was calculated. The inventors have confirmed that the calculated value is in good agreement with the actual measurement result.

FIG. 7 shows the simulation results.
“Vertical position” in FIG. 7 indicates the vertical direction of the screen, and is a position directed upward from the lowest point (lower end) of the backlight unit (optical sheets). In FIG. The results up to where the third lamp is arranged upward are shown.
In addition, as a result of using a lamp having a circular cross-sectional shape (hereinafter also referred to as a “circular lamp”), an elliptical lamp having a non-circular cross-sectional shape (hereinafter referred to as an “elliptical cross-sectional lamp”). This is also shown for comparison of luminance and the like.

(1) A lamp having a circular cross section (“circular lamp” in the figure, indicated by a line a)
In the relationship between the vertical position and the relative luminance value on the backlight light emitting surface using a lamp having a circular cross section, the position close to the lamp, that is, the vertical position is 30 (mm), 100 (mm), 170 (mm). The relative luminance values in the vicinity are 8800 (cd / m ² ), 8700 (cd / m ² ), and 9100 (cd / m ² ), and the average is Lc = about 8870 (cd / m ² ).

Further, the relative luminance values at the positions between the lamps, that is, in the vicinity of 65, 135 (mm) in the vertical direction are 7400 (cd / m ² ) and 7300 (cd / m ² ), and the average is Lb = 7350 ( cd / m ² ), and the ratio of the luminance values of both was Lb / Lc = 0.83.
(2) Oval cross section ("Oval lamp horizontal" in the figure, indicated by line segment b)
Using a lamp with an elliptical section, the long axis of the ellipse is parallel to the backlight surface (horizontal). Relationship between the vertical position on the backlight surface and the relative luminance value. Then, the relative luminance values at positions near the lamp, that is, in the vicinity of 30 (mm), 100 (mm), and 170 (mm) in the vertical direction are 8700 (cd / m ² ) and 8700 (cd / m ² ). , 9000 (cd / m ² ) and the average is Lc = about 8800 (cd / m ² ).

Further, the relative luminance values at the positions between the lamps, that is, in the vicinity of 65 (mm) and 135 (mm) in the vertical direction are 7200 (cd / m ² ) and 7000 (cd / m ² ), and the average is Lb. = 7100 (cd / m ² ), and the ratio between the luminance values of the two was Lb / Lc = 0.81.
(3) Oval cross section ("Oval lamp vertical" in the figure, indicated by line segment c)
Using a lamp with an elliptical cross section, the long axis of the ellipse is arranged perpendicularly to the backlight emitting surface (it is vertical). Relationship between the vertical position on the backlight emitting surface and the relative luminance value Then, the relative luminance values at positions close to the lamp, that is, in the vicinity of 30 (mm), 100 (mm), and 170 (mm) in the vertical direction are 8300 (cd / m ² ) and 8300 (cd / m ² ). 8700 (cd / m ² ), and the average is Lc = about 8430.

Further, the relative luminance values at the positions between the lamps, that is, in the vicinity of 65 (mm) and 135 (mm) in the vertical direction are 7500 (cd / m ² ) and 7300 (cd / m ² ), and the average is Lb = 7400 (cd / m ² ), and the ratio between the luminance values of the two was Lb / Lc = 0.88. Therefore, the luminance ratio is not significantly different among the circular lamp, the elliptical lamp horizontal, and the elliptical lamp vertical, and can be adjusted by the arrangement of the auxiliary reflecting plate and the light shielding material that constitute the optical system of the backlight unit unit.

2-2. Influence of Heat Conducting Member Backlight light emitting surface when lamps having an elliptical cross section and a lamp having a circular cross section are used and each lamp and the housing are connected via the heat conducting member, as in the first embodiment. As a result of investigating the luminance characteristics, the following was found.
(1) Circular cross section In a lamp having a circular cross section, it has been found by the above simulation that light emitted from an outer peripheral surface close to the bottom wall of the outer peripheral surface does not contribute much to the luminance of the backlight light emitting surface.

This is because light emitted from the outer peripheral surface facing the bottom surface of the lamp and the distance between the lamp and the bottom wall of the housing is short between the lamp and the bottom wall (reflection surface) of the housing. This is because the light is absorbed by the lamp and the reflection surface while the reflection is repeated and the light reaching the backlight emission surface is reduced.
As described above, since the heat conducting member is disposed so as to be in contact with the region that does not contribute to the luminance of the backlight light emitting surface in the lamp, it is possible to suppress a decrease in luminance on the backlight light emitting surface. And the area | region which has arrange | positioned the heat conductive member respond | corresponds to the area | region which does not contribute to the brightness | luminance of the backlight light emission surface in a lamp, and since there is little luminance fall by having arrange | positioned the heat conductive member, Naturally, the luminance unevenness with the peripheral portion is also reduced, and as a result, the influence on the luminance unevenness due to the arrangement of the heat conducting member on the backlight emission surface does not appear.

(2) Oval cross section (horizontal)
FIG. 8 is a diagram showing an outline of the path of light emitted to the reflecting surface side in a lamp having an elliptical cross section.
When the lamp having an elliptical cross section is placed horizontally as shown by the solid line in FIG. 8, the region facing the reflecting surface of the casing is reflected by the casing of the circular cross section lamp shown by the phantom line in FIG. It becomes wider than the area facing the surface.

For this reason, a lamp with an elliptical section placed horizontally has a larger number of repeated reflections between the lamp and the bottom wall (reflecting surface) of the casing than a lamp with a circular section, and the backlight emits light. Less light reaches the surface.
Therefore, the area that does not contribute to the brightness of the backlight emitting surface in the lamp is wider in the lamp with the elliptical section placed horizontally than the lamp with the circular section, and the heat conducting member is disposed in this area. The influence on the luminance of the backlight emitting surface is less with a horizontally placed lamp with an elliptical cross section than with a circular cross section lamp.

Similarly, with respect to low luminance unevenness, the lamp with the elliptical cross section placed horizontally is smaller than the lamp with the circular cross section, and the luminance unevenness between the portion where the heat conducting member is arranged and its peripheral portion is also Lamps with an elliptical cross section placed horizontally are smaller than lamps with a circular cross section.
(3) Oval cross section (vertical)
When the lamp having an elliptical cross section is placed vertically, the region facing the reflecting surface of the casing is narrower than the region facing the reflecting surface of the casing in the circular section lamp.

For this reason, a lamp with an elliptical section placed vertically has a smaller number of repeated reflections between the lamp and the bottom wall (reflecting surface) of the casing than a lamp with a circular section, and the backlight emits light. More light reaches the surface.
Therefore, the area that does not contribute to the brightness of the backlight emitting surface in the lamp is narrower in the lamp with the elliptical section placed vertically than the lamp with the circular section, and the heat conducting member is disposed in this area. The influence on the luminance of the backlight light-emitting surface is greater in a lamp with an elliptical section placed vertically than a lamp with a circular section.

Similarly, with respect to local luminance unevenness caused by the reduction of the luminous flux emitted from the lamp by the heat conducting member, the lamp with the elliptical section placed vertically is the lamp with the circular section, and the elliptical section placed horizontally. It will be larger than the lamp that has been turned on.
3. Summary Also in the second embodiment, the heat conduction member described in the first embodiment is used to bring the temperature of the lamp having a non-circular cross-sectional shape close to the optimum temperature with good luminous efficiency, and the backlight. It is considered that the luminance of the light emitting surface can be improved.

In particular, it has been found from the above examination that the influence of the heat conducting member on local luminance unevenness can be reduced by placing a lamp having an elliptical cross section horizontally. In addition, by optimizing the location, size, material, etc. of the heat conduction member, we believe that the luminous efficiency (brightness of the light emitting surface of the backlight) can be increased, and uneven brightness due to the arrangement of the heat conduction member can be minimized. It is done.
Regarding the brightness unevenness when no heat conducting member is provided, the backlight unit in which the lamp having an elliptical cross section is installed in the vertical direction is the best. However, in the experiment, the outer diameter and number of lamps (between the axis of the lamps) If the number of lamps in each backlight unit, the distance between the lamps, etc. are optimized, it is considered that the luminance unevenness can be eliminated.

<Discussion>
1. About Lamp with Oval Section The inventors have conducted various studies (simulations, etc.) when using a lamp with a circular section and using a lamp with an oval section in a horizontal orientation. In a lamp having a cross section, if the ratio E between the tube diameter (long axis) parallel to the bottom wall of the housing and the tube diameter (short axis) perpendicular to the bottom wall is 1.1 or more, It has been found that the effect of suppressing the luminance reduction of the backlight light-emitting surface due to the influence of the conductive member and the local luminance unevenness between the heat conductive member and the periphery thereof are remarkable to the extent that the circular cross section is visible.

2. As to the size of the heat conducting member, as described in the first embodiment, the heat conducting member is an intersection of the line segment Y1 and the outer peripheral surface of the lamp in the cross section of the lamp and is located on the bottom wall side of the housing. If it is a size that contacts within the range of ± 30 degrees around the center of the lamp with respect to the intersection (the size in the cross section of the heat conducting member), the luminance reduction on the backlight emitting surface is practical. The simulation results also showed that there was no problem.

Therefore, in a lamp having an elliptical cross section, the ratio of the tube diameter (long axis) parallel to the bottom wall of the housing to the tube diameter (short axis) perpendicular to the bottom wall is taken as E, and the lamp If the angle at which the bottom of the housing is desired from the center of F is F,
F = ± tan-1 (Etan30 °) = ± tan-1 (0.6E)
If the size of the heat conducting member is within the range of F obtained by

<Modification>
As mentioned above, although this invention was demonstrated based on 1st and 2nd embodiment, the content of this invention is not limited to the specific example shown by said each embodiment, Of course, for example, The following modifications can be implemented.
1. Lamp 1-1. Overall shape Although the lamp shape in each of the above embodiments is a straight tube shape, the hot cathode fluorescent lamp of the present invention is such that the axis of the glass tube constituting the lamp is located on a substantially flat surface. Any shape other than a straight pipe shape may be used.

FIG. 9 is a diagram showing a modification of the backlight unit according to the present invention, in which (a) shows an example using a lamp having a “U” shape, and (b) shows an “N” shape. An example using a lamp is shown.
The backlight unit 211 shown in FIG. 9A includes a housing 213, a plurality of lamps 215 stored in the housing 213, and optical sheets 217. The lamp 215 in this modification is bent at two locations near the center in the longitudinal direction of the glass tube, and has a “U” shape.

  Also in this modification, each lamp 215 is a position corresponding to the outside of the backlight emission surface D2 (a position corresponding to the back side of the peripheral edge) when the backlight unit 211 is viewed from the front. At the position bent in the shape of a letter, it is attached to the inside of the housing 213 via the fixing tool 219, and is a portion corresponding to the backlight emission surface D2 and on the bottom wall 213a side of the housing 213. It is thermally connected to the bottom wall 213 a of the housing 213 through the conductive member 221.

Similar to the first embodiment, the backlight light emitting surface D2 has a position and size substantially corresponding to the screen of a liquid crystal television, is formed inside the peripheral edge 217a of the optical sheet 217, and has a light emitting surface (D2 ) And the peripheral portion 217a is a line segment (including both a solid line and a broken line) C2.
The backlight unit 231 shown in FIG. 9B includes a housing 233, a plurality of lamps 235 stored in the housing 233, and optical sheets 237.

The lamp 235 in this modification is bent at two locations of about 1/3 and 2/3 in the longitudinal direction of the glass tube, and has an “N” shape (S shape).
Also in this modification, each lamp 235 has the fixture 239 at a position corresponding to the outside of the backlight emission surface D3 (a position corresponding to the back side of the peripheral edge) when the backlight unit 231 is viewed from the front. The bottom wall 233a of the housing 233 is disposed on the bottom wall 233a side of the housing 233 via the heat conducting member 241. The bottom wall 233a is attached to the inside of the housing 233 through the heat conducting member 241. Is thermally connected to.

Similar to the first embodiment, the backlight light emitting surface D3 has a position and size substantially corresponding to the screen of a liquid crystal television, is formed inside the peripheral edge 237a of the optical sheet 237, and has a light emitting surface (D3 ) And the peripheral portion 237a is a line segment (including both a solid line and a broken line) C3.
Note that the lamps described in the first and second embodiments, and further the lamp shown in FIG. 9, are straight tubular at the portion corresponding to the backlight emission surface, but may be curved.

Further, the axis of the lamp described in the first and second embodiments, and further, the axis of the lamp shown in FIG. 9 is parallel to the longitudinal direction of the casing, but the axis of the lamp is the longitudinal direction of the casing. It may be inclined with respect to.
Further, the lamps described in the first and second embodiments and the lamp shown in FIG. 9 are arranged so that the axial center thereof is parallel to the longitudinal direction of the casing. You may distribute | arrange so that it may orthogonally cross a direction. In this case, the position of the coldest spot of the lamp moves from the vicinity of the center of the lamp toward the lower part of the liquid crystal display, unlike the embodiments, so that the heat conduction member is placed between the lamp and the housing at that position. Need to be contacted.

FIG. 10 is a view showing a modification of the lamp according to the present invention.
The lamp may be one in which two straight tubular glass tubes as shown in FIG. 10 (a) are bridge-coupled at one end thereof, except for those described in the embodiments and the above modifications. Furthermore, as shown in FIG. 10B, the lamp shape may be a “W” shape. In FIG. 10, the backlight light emitting surface is described as a “light emitting surface” in the drawing so that the positional relationship between the lamp and the backlight light emitting surface can be understood.

1-2. Cross-sectional shape FIG. 11 is a diagram showing a modification of the cross-sectional shape of the lamp according to the present invention.
The cross-sectional shape of the lamp according to the present invention may be other than circular and elliptical shapes. Other shapes include, for example, a polygon such as a triangle and a quadrangle, and an oval. However, if there is a flat part in the cross-sectional shape of the lamp, the flat part is on the bottom wall side of the housing for the reason described in the second embodiment that the lamp having an elliptical cross section is placed horizontally. Thus, it is better to arrange the lamp in the housing.

As shown to (a) of FIG. 11, you may make the cross-sectional shape of a lamp | ramp into a rhombus shape. In this case, it is preferable to arrange so that the longer one of the line segments connecting the opposing apex angles is parallel to the bottom wall of the housing.
Further, as shown in FIG. 11B, the cross-sectional shape of the lamp may be a semicircular shape. In this case, it is preferable to arrange the flat portion of the straight portion that is not an arc so as to be parallel to the bottom wall side of the casing and the bottom wall.

Further, as shown in FIG. 11C, the cross-sectional shape of the lamp may be triangular. In this case, it is preferable to arrange so that the bottom portion is parallel to the bottom wall of the housing.
1-3. Number The number of lamps according to the present invention is not limited to the number shown in the first embodiment and the modification described in FIG. That is, the total discharge path length of the lamp corresponding to the luminance required for the backlight unit is determined by design, and the number of lamps is determined by the discharge path length per lamp. Accordingly, since the discharge path length per lamp varies depending on the lamp shape, the number of lamps is not particularly relevant.

1-4. Outer Diameter of Lamp In the first and second embodiments, the outer diameter of the lamp is not particularly described, but the lamp temperature when the backlight unit is driven obtains good luminous efficiency. The present invention can be applied to any lamp having an outer diameter that is higher than a temperature that can be achieved.
This is because the lamp temperature during driving is determined by the housing, the thermal conductivity of the optical sheets, the thickness of the backlight, etc. The temperature at which good luminous efficiency can be obtained depends on the outer diameter of the lamp. It is because it is decided.

1-5. Fixing tool In the above-described embodiment and modification, the fixing tool for the lamp was not particularly described. However, the lamp may be held at a position corresponding to the back side of the peripheral region of the optical sheet (front surface of the case). The fixing tool for fixing the lamp may be on the bottom wall and the side wall constituting the housing.
2. 2. Thermal conduction member 2-1. Size The heat conductive member according to the present invention is not particularly limited in shape, material, and the like. That is, the heat conducting member according to the present invention only needs to be capable of lowering the temperature at the time of lamp lighting by contacting the lamp and transferring heat at the time of lamp lighting to the casing.

The material of the heat conducting member is determined by the outer diameter of the lamp used in the backlight unit and the temperature of the lamp when the backlight unit is driven.
In other words, if there is a large difference between the lamp temperature when the lamp is lit and the optimum temperature at which the luminous efficiency is the best, it is necessary to transfer a large amount of heat from the lamp when lit to the housing, and the contact area with the lamp is reduced. It is necessary to increase the size or use a material with good thermal conductivity.

Conversely, if the difference between the lamp temperature when the lamp is lit and the optimum temperature at which the luminous efficiency is the best is small, there is no need to transfer the heat from the lamp when lit to the housing, and the contact area with the lamp is reduced. This can be dealt with by reducing the size or using a heat conducting member with poor heat conductivity.
The thermal conductivity of the heat conducting member is desirably 10 (W / m / K) or more. When the thermal conductivity is less than this value, in the lamp having an outer diameter of 30 (mm) or less, the contact area of the heat conducting member with the lamp is increased in order to quickly increase the luminance efficiency after lighting, and the local This is because uneven brightness is visually recognized. In addition, stainless steel, iron, aluminum etc. are mentioned as a member which has the said heat conductivity.

2-2. Others In each embodiment, polycarbonate is used for the heat conducting member. However, for example, it may have a function of reflecting light from a lamp. By having a reflective function, a decrease in luminance can be suppressed by providing a heat conductive member.
As an example of the heat conducting member having such a reflection function, there is a case where a reflection film is formed on a portion of the polycarbonate that contacts the lamp, or the contact portion is made of metal and the contact portion is mirror-finished. is there.

2-3. Structure The structure of the heat conducting member according to the present invention is not limited to the structure of the heat conducting member described in the first and second embodiments.
FIG. 12 is a view showing a modification of the heat conducting member.
As shown in the figure, the heat conducting member 271 is attached to the bottom wall 159a of the housing 159, and inside the housing 159 and on the outer peripheral surface of the lamp 103, as in the second embodiment. A contact portion 271a that is in contact with the housing, a heat dissipating portion 159b that is located outside the housing 159 and dissipates the heat of the lamp 103 to the outside of the housing 159, and a through-hole in the bottom wall 159a of the housing 159 A connecting portion 271c for connecting the contact portion 271a and the heat radiating portion 271b is provided. Here, the abutting portion 271a is configured by a plate member and has a spring function.

  The heat conducting member (contact portion) of the present invention is made of a material having a light reflectance equivalent to that of the reflecting surface, or the light conducting surface of the heat conducting member has a light reflectance equivalent to that of the reflecting surface. By coating the substance, it is possible to improve the amount of light flux from the lamp reaching the liquid crystal panel surface, and to improve local luminance unevenness due to the reduction of the light flux amount at the contact portion of the heat conducting member.

3. Others The lamp unit of the present invention can be applied to other than the backlight unit described above.
FIG. 13 is a diagram showing an example in which the present invention is applied to a lighting device.
As shown in FIG. 13, the lighting device 301 is mounted on, for example, a ceiling 302. The lighting device 301 turns on the lamp 303, a housing 305 for housing the lamp 303, a diffusion member 307 for preventing light from the lamp 303 from being directly emitted to the outside of the device, and the lamp 303. A lighting circuit 309.

  Also in this case, the “case” of the present invention includes the housing 305 and the diffusion member 307, and the front surface of the case serves as the diffusion member. In each of the above embodiments and this modification, the case of the present invention is composed of a box-shaped housing and plate-shaped optical sheets (diffusing members). ), A cylindrical body serving as a box-shaped side wall, and plate-shaped optical sheets (diffusion members), or a base plate, and a cylindrical body and optical sheets are integrated. It may be configured.

The diffusing member 307 has a peripheral portion 307 a that does not transmit light, and a central portion surrounded by the peripheral portion 307 a is a light emitting surface 307 b of the lighting device 301.
The lamp 303 is attached to the housing 305 at a portion corresponding to the peripheral edge portion 307 a of the diffusing member 307, and the lamp 303 is a portion corresponding to the light emitting surface of the diffusing member 307 and the bottom wall of the housing 305. It is thermally connected to 305a via a heat conducting member 311.

  In this example, the outer diameter of the lamp is 18 (mm), and the distance between the reflecting surface and the optical sheet is 30 (mm) and 40 (mm).

  ADVANTAGE OF THE INVENTION According to this invention, the brightness | luminance as a unit can be improved using a hot cathode fluorescent lamp, and a lamp unit which can make brightness nonuniformity small can be provided.

FIG. 1 is an exploded perspective view showing a schematic configuration of the liquid crystal television according to the present embodiment. FIG. 2 is a cross-sectional view of the virtual plane X in FIG. 1 as viewed from the direction of the arrow. FIG. 3 is a view of the backlight unit as viewed from the liquid crystal panel side, and optical sheets and the like are cut away so that the inside can be seen. FIG. 4 is a diagram illustrating the configuration of the lamp, and a part of the lamp is cut away so that the inside can be seen. FIG. 5 is a diagram showing a contribution ratio of a light beam emitted from a divided region of the lamp to a backlight light-emitting surface light beam. FIG. 6 is a cross-sectional view when the backlight unit according to the second embodiment is cut along a virtual plane corresponding to the virtual plane X in FIG. 1. FIG. 7 shows the simulation results. FIG. 8 is a diagram showing an outline of the path of light emitted to the reflecting surface side in a lamp having an elliptical cross section. FIG. 9 is a diagram showing a modification of the backlight unit according to the present invention, in which (a) shows an example using a lamp having a “U” shape, and (b) shows an “N” shape. An example using a lamp is shown. FIG. 10 is a view showing a modification of the hot cathode fluorescent lamp according to the present invention. FIG. 11 is a view showing a modification of the cross-sectional shape of the hot cathode fluorescent lamp according to the present invention. FIG. 12 is a view showing a modification of the heat conducting member. FIG. 13 is a diagram showing an example in which the present invention is applied to a lighting device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal television 5 Backlight unit 7 Lamp 9 Case 9a Bottom wall 35 Heat conduction member 301 Illumination device

Claims (12)

In a lamp unit in which a hot cathode fluorescent lamp is housed in a case and emits light in front of the case from a central region excluding a peripheral region on the front surface of the case,
The hot cathode fluorescent lamp is held in the peripheral area of the front surface of the case when the case is viewed from the front side thereof.
A portion corresponding to the central region in the hot cathode fluorescent lamp is in contact with the bottom surface of the case via a heat conducting member.   2. The lamp unit according to claim 1, wherein the bottom surface of the case is a reflection surface that reflects light from the hot cathode fluorescent lamp forward.   The lamp unit according to claim 1 or 2, wherein an outer peripheral length in a cross section of a glass tube constituting a discharge space of the hot cathode fluorescent lamp is in a range of 47 mm or more and 95 mm or less. The glass tube has a substantially circular cross-sectional shape,
In the cross section of the glass tube, the heat conducting member is an intersection of a line segment orthogonal to the front surface of the case and passing through the center of the glass tube and the outer periphery of the glass tube, and is located on the bottom surface side of the case 4. A part of or all of the outer peripheral region connecting the outer peripheral positions of the glass tubes displaced by ± 30 degrees around the center of the glass tube with respect to the point to be touched. Lamp unit.   4. The lamp unit according to claim 3, wherein the glass tube has a non-circular cross-sectional shape, and a portion of the glass tube located on the side opposite to the central region has a flat shape. .   6. The lamp according to claim 3, wherein the glass tube has a non-circular cross-sectional shape, and a diameter in a direction parallel to the bottom surface of the case is larger than a diameter in a direction perpendicular to the bottom surface. unit.   7. The lamp unit according to claim 5, wherein a cross-sectional shape of the glass tube is a substantially elliptical shape or a substantially oval shape, and a ratio of a minor axis to a major axis is 1.1 or more.   The lamp unit according to any one of claims 1 to 7, wherein the heat conducting member is made of a material having a thermal conductivity of 10 W / m / K or more.   The thermal conductive member thermally connects the hot cathode fluorescent lamp and the case at or near the coldest spot of the hot cathode fluorescent lamp. The lamp unit according to the item.   10. The lamp unit according to claim 1, wherein an area of the heat conducting member that contacts the hot cathode fluorescent lamp is smaller than an area that contacts the bottom surface.   The lamp unit according to claim 1, wherein the heat conducting member has a structure that penetrates the bottom wall of the case and is thermally coupled to the outside of the case.   The heat conducting member is made of a material having a light reflectance equivalent to that of the reflecting surface, or the surface of the heat conducting member is coated with a material having a light reflectance equivalent to that of the reflecting surface. The lamp unit according to claim 2.

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