JPS62200332A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To display a clear pattern high in contrast independently of the change in ambient brightness by constituting a light source places at the rear of a liquid crystal cell so that the quantity of light of this light source is automatically controlled in accordance with the brightness around the liquid crystal cell. CONSTITUTION:If it is relatively dark around the liquid crystal cell when the liquid crystal cell incorporating a liquid crystal 4 is driven to emit light for display, a gate circuit 14 is turned off because a photocurrent is not generated in a sensor 8, and the liquid crystal cell is not irradiated with a light source 6 to emit light. If it is bright around the liquid crystal cell, the photocurrent is generated in the sensor 8 to turn on the circuit 14, and voltage from a power source 7 is applied to the light source 6 in accordance with the increase of the photocurrent of the sensor 8. A control part 9 applies such voltage to the light source 6 that a ratio of the optical energy per unit area due to the light source 6 to that per unit area of ambient light of the liquid crystal cell is a certain value. Thus, clear patterns high in contrast are displayed with the liquid crystal independently of the change of ambient brightness.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a transmissive liquid crystal display device, and particularly to the structure of a light source for transmissive illumination thereof.

[Prior art and problems to be solved by the invention] This type of liquid crystal display device has a transmissive liquid crystal display cell and a light source for transmissive illumination, and conventionally performs color display as shown in FIG. 3, for example. In this case, the basic structure of the liquid crystal cell C is a pair of glass substrates 1.1 each having a transparent electrode 2°2' formed into a predetermined pattern using a photomask or the like.
A patterned color filter 3 and a twisted nematic liquid crystal 4 are interposed between them, and a polarizing plate 5.5 is disposed on the outside of both substrates 1.1.On the other hand, the light source 6 is connected to a switch S by a power source 7. Alternatively, it is configured to be turned on via a manual dimming device that cooperates with this. Moreover, transparent electrode 2. .

2 is connected to a driving power source (not shown),
When an electric field is applied between the two electrodes 2,2'', the liquid crystal cell C emits light according to the pattern of the electrodes 2,2'', and is irradiated by the light source 6, so that the light emitting display pattern is displayed more clearly. It has become.

However, in such a conventional display device, the liquid crystal cell C
is illuminated from behind by the light source 6, but since the amount of light from the light source 6 is always constant, if the surrounding brightness changes, for example if it becomes brighter, the contrast of the light emitting display pattern of the liquid crystal cell C will change. In view of the above circumstances, it is an object of the present invention to provide a liquid crystal display device that can always provide a clear luminescent display even when the surrounding brightness changes.

Means and Effects for Solving Problem c] The liquid crystal display device according to the present invention is configured such that the amount of light from the light source that illuminates the liquid crystal cell can be automatically adjusted in accordance with the surrounding brightness. Therefore, even if the surrounding brightness changes in brightness or darkness, a clear light emission display pattern can always be obtained without being affected by it.

〔Example〕

1 and 2 show an embodiment of a liquid crystal display device according to the present invention. In FIG. 1, 6 is a light source that can illuminate the liquid crystal cell C from behind, and 7 is a power source that can light the light source 6. , 8 is a photoconductive element such as a photodiode, and is capable of detecting the brightness around the liquid crystal cell C without directly receiving the light emitted from the light source 6; 9 is the sensor 8;
The control unit that receives the detection signal is a control unit that can send the output of the power supply 7 to the light source 6 via the lighting device 10 depending on the brightness around the liquid crystal cell C. Specifically, in the figure, 11 is an oscillator, 12 is an amplifier for amplifying the signal of the oscillator, and 13 is a Toulon circuit. This is a timing circuit that sends out gate input signals.

Since the liquid crystal display device according to the present invention is configured as described above, when the liquid crystal cell C is driven to perform a light emitting display, if the surrounding area is relatively dark, no photocurrent is generated in the sensor 8, so the gate circuit 14 is in the OFF state, the light source 6 is not driven, and the liquid crystal cell C is not irradiated with light by the light source 6 and emits light as it is. Next, when the surroundings of the liquid crystal cell C become bright, a photocurrent is generated in the sensor 8. However, since the current increases with the brightness of the surroundings, the gate circuit 14 turns on, and as the photocurrent of the sensor 8 increases, the voltage from the power source 7 is applied to the light source 6. At this time, the control unit 9 applies a voltage to the light source 6 so that the ratio of the light energy per unit area of the light source 6 to the energy per unit area of the light around the liquid crystal cell C becomes a constant value, so that the light R6 can always irradiate the liquid crystal cell C with an appropriate amount of light depending on the brightness around the liquid crystal cell C, and thereby a clear pattern display of the liquid crystal cell C can be obtained even if the surrounding brightness changes.

The liquid crystal cell C in the above embodiment may be a transmissive color liquid crystal, such as a guest host type or a twisted nematic liquid crystal, and the light source 6 may be a general filament type light bulb, cold cathode tube, or LED.

An EL or the like may be used, and various photoelectric elements such as a phototransistor in addition to a photodiode may be used as the sensor 8, and in either case, patterned light emission display with good contrast can be performed. Furthermore, the same effect can be obtained even if the control section 9 is configured with a photodiode and a differential amplifier.

〔Effect of the invention〕

As described above, the liquid crystal display device according to the present invention can always display a clear pattern with high contrast regardless of changes in ambient brightness, and has an extremely excellent practical advantage.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the overall configuration of an embodiment of the liquid crystal display device of the present invention, FIG. 2 is a block diagram showing the configuration of a light source for illuminating a liquid crystal cell having an automatic dimming function according to the present invention, and FIG. The figure is a diagram showing the configuration of a conventional liquid crystal display device. 1.1'...Substrate, 2.2'...Transparent electrode, 4
...LCD, 6..Light source, 7..Power supply, 8.
...Sensor, 9...Control unit, 11...Emitter, 12...Amplifier, 13...Timing circuit, 14...Gate circuit, C...Liquid crystal cell. Figure 1 yP2 Figure 51-3 Procedural amendment (voluntary) April 30, 1985

Claims (1)

[Claims] In a liquid crystal display device in which a light emitting display is performed by transmitting illumination of a liquid crystal cell by a light source placed behind it when the liquid crystal cell emits light, the light source automatically adjusts the amount of light according to the brightness around the liquid crystal cell. 1. A liquid crystal display device, characterized in that it is configured to be adjustable.