Backlight unit structure for liquid crystal display

[0001] 1. Field of the Invention

[0002] The present invention relates to a backlight unit for a liquid crystal display (LCD), and more particularly to a backlight unit structure for a liquid crystal display having a blink backlight structure provided with a reflection plate to allow for improvement of a response time and accomplishment of a high luminance.

[0003] 2. Description of the Prior Art

[0004] In order to improve a response time in an LCD, a technique using a high-speed response liquid crystal has been employed in general. In addition, the response time may be further improved by utilizing the panel structures such as a VA (Vertical Alignment) panel structure, an IPS (In Plane Switch) panel structure, an OCB (Optically Compensated Bend) panel structure and so forth, rather than a typical TN (Twisted Nematic) panel structure. Yet another technique of improving the response time may be to select a driving method such as a CCD driving method over others.

[0005] Even though the above-mentioned various techniques have been used to improve the response time, it has been impossible to acquire the same response time as a CRT (Cathode Ray Tube).

[0006] This results from a display principle of the CRT, which is based on an impulse light emission system. That is, the CRT is displayed by emitting light once (2-3 ms) a frame (16.7 ms, 60 Hz).

[0007] However, because the LCD emits light in succession (16.7 ms) during one frame, a blur phenomenon is generated while the LCD is displayed, unlike the CRT. In particular, in the case of a moving picture, a serious mismatch phenomenon wherein image signals are mismatched with the eyes of a user is generated from the LCD. This mismatch phenomenon is a common phenomenon found not only in an LCD but also in display devices using a method of steadily emitting light, such as a plasma display panel (PDP) and an electroluminescence (EL) display.

[0008] As shown in FIGS. 1a and 1b, an impulse system is realized by providing a plurality of lamps 13 in a backlight module 11 disposed under a display panel 15, and then by performing a sequential turning on/off according to a principle similar to that in a CRT display.

[0009] Here, to obtain a satisfactory display image quality, the sequential turning on/off is synchronized with a gate signal at the same time. In other words, as in FIG. 2, lamps 13 located under a gate line become on-state when the gate signal is applied to the gate line, while the lamps 13 become off-state when the gate signal is not applied to the gate line. That is, the on-state of the lamps 13 is gradually shifted from the upper side of the display to the lower side thereof.

[0010] According to research data of Hitachi Inc., when the sequential turning on/off mode is used in a blink backlight system having six lamps, a luminance is reduced at 16% compared with a system in which the lamps are continuously turned on. When a duty time of the lamp is set to 60%, luminance of 60% can be obtained.

[0011] As the duty time becomes shorter, a trade-off relationship ensues, in which a moving picture becomes clearer but the luminance becomes reduced. The research data of Hitachi Ltd. reports that a minimum duty time for reducing the blur phenomenon in a moving picture of an LCD is 70%.

[0012] Further, as a tube current of a typical luminous body (CFL (Color Cathode Fluorescent Lamp)) is growing high, a temperature of the lamp is increased, and thus an efficiency of the luminance is decreased.

[0013] In the blink backlight system, because the off-state of the lamp prevents the temperature of the lamp from increasing, there is a room to increase the tube current compared with the lamp in a steady on-state, so that the luminance can be increased.

[0014] Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a backlight unit structure for an LCD having a blink backlight structure mounted with a reflection plate, so as to improve a response time and to obtain a high luminance.

[0015] In order to accomplish this object, there is provided a backlight unit structure for an LCD (Liquid Crystal Display), comprising: a lamp disposed under a display panel; and a reflection plate rotatably disposed around the lamp and having an opening through which light can be concentrated on the display panel.

[0026] Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. In the following description and drawings, the same reference numerals are used to designate the same or similar components, and so repetition of the description on the same or similar components will be omitted.

[0027] FIG. 3a is a top view of a blink backlight having a reflection plate in accordance with the present invention. FIG. 3b is a cross-sectional view taken along line IIIb—IIIb of FIG. 3a. FIG. 3c is a magnified view of part A of FIG. 3b.

[0028] FIG. 4 shows variation in the direction of light and display area depending on time, in a blink backlight structure for an LCD according to the present invention.

[0029] Further, FIG. 5 is perspective view of a blink backlight having a reflection plate in accordance with one embodiment of the present invention. FIG. 6 is a cross-sectional view of a blink backlight having a reflection plate in accordance with another embodiment of the present invention.

[0030] The present invention proposes a method capable of decreasing the duty time without sacrifice of luminance, in consideration of the fact that a clear moving picture may be obtained by decreasing a duty time in a blink backlight system.

[0031] In a backlight unit structure 21 according to the present invention, as shown in FIGS. 3A to 3C and 4-6, the structure 21 has a plurality of lamp units 23 and rotation driver 31 and is disposed below a display panel. Each of the lamp units 23 is provided with a backlight lamp 23a and a reflection plate 27, the reflection plate 27 being spaced a predetermined distance apart from the backlight lamp 23a, and then is turned by a rotation driver 31.

[0032] Further, each of the reflection plates 27 is formed integrally with the corresponding backlight lamp 23a so that the reflection plate 27 can rotate together with the backlight lamp 23a. Further, each of the reflection plates 27 surrounding the corresponding backlight lamp 23a has a structure shaped like a partly broken cylinder, that is, has a sectional shape of a perforated circle having an opening through which light can be concentrated and collected on the display panel.

[0033] Further, it is important to harmonize a rotation speed of the backlight lamp 23a with a scanning speed of a gate signal. In other words, light of the backlight lamp is concentrated on a pixel synchronized with the signal.

[0034] Therefore, the method technically allows the duty time to reduce a scanning time of the gate signal in the blink backlight, so that it is possible to reduce a blur phenomenon of the moving picture and to maximize an efficiency of light. As a result, a luminance can be enhanced.

[0035] FIG. 4 shows the variation in the directed light area 29 on the display panel 25 due to the rotation of the backlight lamp 23a and/or the reflection plate 27.

[0036] FIGS. 5 and 6 show a blink backlight having a reflection plate according to the present invention in detail, in which the reflection plate 27 is turned separately from the backlight lamp 23a by a rotation driver 31.

[0037] That is, a blink backlight 21 is realized by fixing a backlight lamp 23a, and then by rotating a reflection plate 27 together with the rotation driver 31. At this time, a rotation speed of the reflection plate 27 is adapted to match with the scanning speed of the gate.

[0038] As mentioned above, with the backlight unit structure for the LCD in accordance with the present invention, the blink backlight having the reflection plate is applied, so that it is possible to improve a response time, to enhance an image quality of the moving picture similarly to the existing CRT, and to obtain a high luminance as well.

[0039] Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.