JP2006286287A - Light control method of lighting device, lighting apparatus and liquid crystal display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light control method of a lighting device which can easily independently adjust the luminance and the temperature of a plurality of cold cathode fluorescent lamps, and to provide a lighting apparatus, as well as a liquid crystal display apparatus. <P>SOLUTION: The liquid crystal display apparatus 1 has a lighting apparatus 2 as a backlight light source for illuminating a liquid crystal panel 8. By using a method of adjusting the lighting apparatus 2, having a plurality of cold cathode fluorescent lamps 3 by burst dimming, either the luminance or the heating temperature of an arbitrary one among the cold cathode fluorescent lamps 3 is adjusted, while the other is kept at a fixed level so that the luminance unevenness and/or temperature distribution unevenness in the lighting apparatus 2 can be eliminated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a dimming method for an illuminating device, an illuminating device dimmed by the dimming method, and a liquid crystal display device using the illuminating device.

  Conventionally, a liquid crystal display device using a cold cathode fluorescent lamp having high luminance and high color rendering characteristics as a light source (called a backlight) for illuminating a liquid crystal panel is well known.

  In general, such a liquid crystal display device is configured so that the brightness (luminance of the display screen) of the light emitting surface can be adjusted by changing the brightness (light quantity) of the cold cathode fluorescent lamp (so-called dimming).

For this dimming, a dimming method called current dimming is widely adopted (for example, Patent Document 1). Current dimming makes use of the fact that the brightness of a cold cathode fluorescent lamp is proportional to the magnitude of its conduction current. The high-frequency current is continuously conducted through the cold cathode fluorescent lamp, and the brightness is changed while changing the current value. (See FIG. 3).
JP-A 61-195599

  In recent years, there is a tendency in the market to increase the size and brightness of liquid crystal display devices such as liquid crystal televisions. In this case, an illuminating device having a so-called direct-type backlight configuration in which a plurality of light sources (cold cathode fluorescent lamps) are arranged immediately below the liquid crystal panel to illuminate the liquid crystal panel is widely employed ( (See FIG. 1).

  Such an illuminating device equipped with a plurality of cold cathode fluorescent lamps has not only unevenness in brightness (illumination) due to variations in characteristics (gas pressure, phosphor film thickness, etc.) of each cold cathode fluorescent lamp. There is a characteristic that illumination unevenness easily occurs due to mutual influence of the heat generation temperature of the fluorescent lamp (that is, due to temperature distribution unevenness). In addition, the LCD panel responds sensitively to changes in temperature and changes the brightness and color, making it difficult to design color filters. Use lighting devices with multiple cold cathode fluorescent lamps. In such a liquid crystal display device, it can be said that adjustment of the heat generation temperature of each cold cathode fluorescent lamp is a particularly important factor.

  By the way, in the current dimming described above, the amount of heat generated by the cold cathode fluorescent lamp also changes in proportion to the magnitude of the conduction current (see FIG. 3C). That is, in current dimming, the variation tendency of the heat generation temperature of the cold cathode fluorescent lamp shows the same tendency as the luminance. This means that, in current dimming, it is almost impossible to independently adjust the brightness or heat generation temperature.

  Therefore, with such current dimming, it can be said that it is very difficult to accurately and easily adjust the brightness of an illuminating device including a plurality of cold cathode fluorescent lamps, particularly for a liquid crystal display device using the illuminating device. Is a factor that hinders high brightness.

  The present invention has been made to solve the above-described problems, and for each of a plurality of cold-cathode fluorescent lamps included in the lighting device, the luminance or temperature is adjusted independently, thereby causing uneven lighting or temperature of the lighting device. It is an object of the present invention to provide a dimming method for an illuminating device capable of eliminating uneven distribution, an illuminating device dimmed by the dimming method, and a liquid crystal display device using the illuminating device.

  The dimming method of the illuminating device of the present invention is a method of dimming an illuminating device comprising a plurality of cold cathode fluorescent lamps by burst dimming, and any one of the luminance or heat generation temperature of the cold cathode fluorescent lamp is selected. By adjusting the other while keeping one constant, the illumination unevenness and / or temperature distribution unevenness of the illumination device can be eliminated.

  Moreover, the liquid crystal display device of the present invention is characterized in that the illuminating device dimmed by the dimming method is used as a backlight light source for illuminating the liquid crystal panel.

  The dimming method of the lighting device having the above configuration is characterized in that burst dimming (also referred to as duty dimming or PWM dimming) is employed. Such burst dimming is a method of performing dimming while changing the ratio of the conduction time (ON time) of the high-frequency current supplied to the cold cathode fluorescent lamp and its current value. Normally, current dimming has a problem that the range of dimming is narrowed due to the limitation of the current value guaranteed by the cold cathode fluorescent lamp manufacturer. However, in burst dimming, the ON time ratio is substantially stepless. Therefore, the light can be dimmed with accuracy over a wider range.

  In burst dimming, as a general phenomenon, the luminance and heat generation temperature of a cold cathode fluorescent lamp do not show the same fluctuation tendency. Therefore, for each cold cathode fluorescent lamp, it is possible to adjust the heat generation temperature while keeping the brightness constant, and conversely, it is possible to adjust the brightness while keeping the heat generation temperature constant. Even if there are a plurality of lamps, the illumination unevenness and temperature distribution unevenness of the illumination device can be eliminated, and the brightness can be adjusted to an appropriate level.

  And it becomes possible to provide the liquid crystal display device excellent in quality even if it is large sized by using the illuminating device light-modulated by this light modulation method as a backlight light source.

  As described above, the light control method of the lighting device of the present invention can adjust the luminance or heat generation temperature independently and accurately for each of the cold cathode fluorescent lamps, even if a plurality of cold cathode fluorescent lamps are provided. Therefore, it is easy to adjust the appropriate brightness without uneven illumination.

  In addition, by using an illuminating device that has been dimmed by the dimming method of the illuminating device as a backlight light source, it is possible to provide a liquid crystal display device that is large, has high brightness, and can be easily designed with a color filter.

  Hereinafter, a light control method, a lighting device, and a liquid crystal display device of a lighting device according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of a liquid crystal display device 1 according to this embodiment. In FIG. 1, the liquid crystal display device 1 includes an illumination device 2 and a liquid crystal panel 8. The illuminating device 2 includes a plurality of cold cathode fluorescent lamps 3, a reflective case (reflecting plate) 4, a light guide plate 5, a light collecting sheet 6, and a diffusion sheet 7, and illuminates the liquid crystal panel 8 as a so-called direct type backlight. .

  Dimming of the illumination device 2 is performed by burst dimming (also called duty dimming or PWM dimming). The burst dimming is performed by controlling the ratio of the ON time related to the oscillation operation of the inverter circuit (not shown), thereby controlling the ratio of the conduction time (ON time) of the high-frequency current supplied to each cold cathode fluorescent lamp 3 (in other words, lighting This is a method of dimming by changing the time ratio and changing the current value (see FIG. 2).

  In such burst dimming, as shown in FIG. 2D, the luminance value can be adjusted within a predetermined range at a predetermined current value (for example, A2) (for example, L1 to L3).

  Further, as a further feature of burst dimming, when the luminance value is adjusted to a predetermined value (for example, L2), the current value (for example, A1 to A3) as an adjustment parameter and the ON time ratio (FIG. 2 (a)). The combination of (c)) can be set steplessly. If the combinations of such adjustment parameters are different, the heat generation temperature changes as a general phenomenon. Therefore, by using such a phenomenon, it is possible to adjust the temperature (heat generation temperature) while maintaining the luminance at a predetermined value.

  On the other hand, it has been found that the heat generation temperature is also similar to the graph shown in FIG. Therefore, it is possible to adjust the luminance while maintaining the temperature at a predetermined value.

  As described above, since the dimming method of the lighting apparatus according to the present embodiment of the present invention employs burst dimming, it is possible to adjust the luminance within a wide range.

  Further, for each cold cathode fluorescent lamp 3, it is possible to adjust the heat generation temperature while keeping the brightness constant, and conversely, the brightness can be adjusted while keeping the heat generation temperature constant. Even if there are a plurality of fluorescent lamps 3, it is easy to adjust to an appropriate brightness without uneven illumination or uneven temperature distribution. In particular, since the temperature distribution unevenness can be eliminated, the quality of the liquid crystal display device 1 including the illumination device 2 dimmed by the dimming method is excellent.

  In addition, the light control method of the illuminating device, the illuminating device, and the liquid crystal display device according to the present invention are not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

  For example, the burst dimming of the above embodiment is a PWM method in which the oscillation frequency is fixed and the ratio of the ON time is changed, but the ON time and the OFF time are changed by fixing the ON time and changing the oscillation frequency. A PFM method in which the ratio is changed can also be adopted.

  The dimming method of the lighting device according to the present invention is suitable for use as a backlight light source in a liquid crystal display device because it can easily and accurately perform dimming of a plurality of cold cathode fluorescent lamps. Application to a liquid crystal display device such as a liquid crystal television requiring high brightness is useful.

Sectional drawing of the liquid crystal display device which concerns on one Embodiment of this invention (A)-(c) is a waveform figure of the high frequency current in burst dimming, (d) is a figure which shows the relationship between the electric current value and brightness | luminance in burst dimming. (A) And (b) is a waveform figure of the high frequency current in current dimming, (c) is a figure showing the relation between the current value and luminance (or temperature) in current dimming.

Explanation of symbols

1 Liquid crystal display device 2 Illumination device

Claims (3)

A method of dimming a lighting device comprising a plurality of cold cathode fluorescent lamps by burst dimming,
The brightness or heat generation temperature of any of the cold cathode fluorescent lamps is configured to be able to eliminate illumination unevenness and / or temperature distribution unevenness of the illumination device by adjusting one while keeping either one constant. A lighting control method for an illuminating device.   An illumination device that is dimmed by the dimming method according to claim 1. A liquid crystal display device, wherein the illumination device according to claim 2 is used as a backlight light source for illuminating a liquid crystal panel.

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