JP2000098332A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a flicker in a screen by preventing a light source from turning on/off even when illuminance of an external beam is changed alternately at nearly 1,000 lux in a short time when the light source is turned off, and a display is performed only by the external beam when the illuminance of the external beam is e.g. 1,000 lux or above, in a liquid crystal display device simultaneously using both of the beam from the light source and the external beam and performing the display. SOLUTION: For instance, when the illuminance of the external beam is changed from 1,000 lux or above to 1,000 lux or below at the point of time of t1, when the illuminance of the external beam detected by an illuminance detection sensor is 1,000 lux or below continuously till the point of time of t2 when a prescribed time elapses from the point of time of t1, the light source is turned on at the point of time of t2. When not so, the light source is left turned off.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device having a non-light emitting type display panel such as a liquid crystal display panel.

[0002]

2. Description of the Related Art A display device having a non-light-emitting type display panel such as a liquid crystal display panel is roughly classified into a transmission-type display device using transmitted light and a reflection-type display device using reflected light. There is a reflective type for displaying, and a reflective and transmissive type that combines these two types. In the case of a reflective and transmissive display device, although not shown, a transflective semi-reflective plate is generally arranged on the back side of a non-emissive display panel, and a backlight is arranged on the back side. It has a structure. And when used as a transmissive type, the backlight is turned on, the light from the backlight is transmitted through the semi-transmissive semi-reflective plate and the display panel, and emitted to the front side of the display panel,
The display is thereby performed. On the other hand, when used as a reflection type, the backlight is not turned on, and external light incident from the front side of the display panel is transmitted through the display panel and reflected by the transflective plate, and the reflected light is displayed. The light is transmitted through the panel and emitted to the front side of the display panel, thereby performing display.

[0003]

By the way, in such a display device, display can be performed by simultaneously using both light from the backlight and external light. However, in an environment in which sufficient screen luminance can be obtained only by external light, when display is performed by simultaneously using both light from the backlight and external light, power is wasted. Therefore, the illuminance of the external light is detected by the illuminance detection sensor, and based on the detection result, the backlight is turned off when the illuminance of the external light is equal to or higher than a predetermined illuminance, and the illuminance of the external light is set to a predetermined illuminance. If the illuminance is less than the illuminance, the backlight may be turned on. However, when the illuminance of the external light alternates between a higher illuminance and a lower illuminance than a predetermined illuminance in a short time, for example, when the train passes the iron bridge in the daytime, sunlight is intermittently blocked by the iron bridge. In such a case, the backlight blinks, and the screen of the display panel flickers. It is an object of the present invention to prevent a screen of a display panel from flickering even when the illuminance of external light alternates between an illuminance higher than a preset illuminance and a lower illuminance in a short time.

[0004]

According to the present invention, there is provided a non-light-emitting type display panel, and a light-emitting type display panel disposed on the back side of the display panel for emitting light toward the back side of the display panel. Reflection / light emitting means for reflecting external light incident from the side and passing through the display panel toward the back surface of the display panel, detecting environmental illuminance, and calculating a change in environmental illuminance within a preset time. A light emission control means for controlling the light emission of the reflection and light emission means based on the calculation result. According to this invention, when the light emission control means controls the light emission of the reflection / light emission means based on a change in the environmental illuminance (illuminance of external light) within a preset time, the environmental illuminance is set in advance. When the light emission control means ignores this when the illuminance changes higher and lower than the preset illuminance within a predetermined time, the environmental illuminance is higher than the preset illuminance. Even if the illuminance alternates with the low illuminance in a short time, the screen of the display panel can be prevented from flickering.

[0005]

FIG. 1 shows a main part of a reflection / transmission type liquid crystal display device to which an embodiment of the present invention is applied. This liquid crystal display device includes a non-light emitting type liquid crystal display panel 1. Although not shown in detail, the liquid crystal display panel 1 has a pair of glass substrates 2 and 3 bonded to each other with a substantially frame-shaped sealing material 4 interposed between the two glass substrates 2 and 3 inside the sealing material 4. Liquid crystal is sealed, and polarizing plates 5 and 6 are attached to the surfaces of the glass substrates 2 and 3. As the liquid crystal display panel 1 in this case,
Any of a segment system, a simple matrix system, an active matrix system, etc. may be used, and a TN (twisted nematic) type, STN (super twisted nematic) type, ECB (birefringence effect) type, etc. may be used. In short, any non-light-emitting type may be used.

On the back side of the liquid crystal display panel 1, a backlight (reflection / light emitting means) 11 having a reflection function is arranged. The backlight 11 includes an optical sheet 12 provided on the back surface of the liquid crystal display panel 1 and the optical sheet 12.
A light diffusion layer 13 provided on the back surface of the light diffusion layer 13;
An optical member 14 provided on the back surface of the optical member 14;
And a light source 16 provided on a predetermined one end surface side of the light guide 15.
The light source 16 includes a linear fluorescent tube 17 and a reflector 18 for reflecting light from the fluorescent tube 17 toward one end surface of the light guide 15.

As shown in FIG. 2, the light guide 15 is made of an acrylic resin or the like, and has a flat back surface and a predetermined one end surface perpendicular to the back surface.
The surface has a step-like structure that gradually becomes thinner from the light incident surface 21 side to the other end surface side. In this case, the step-like surface includes a plurality of step surfaces 22 parallel to the back surface and a step surface (light emitting surface) 23 perpendicular to these step surfaces 22. On each of the step surfaces 22, a reflection film 24 made of a deposited film of aluminum or the like is provided via a base film (not shown) made of silicon oxide. A reflection plate 25 is provided on the back surface of the light guide 15. The light guide 15 is disposed on the back surface side of the liquid crystal display panel 1 with its back surface appropriately inclined with respect to the liquid crystal display panel 1.

As shown in FIG. 2, the optical member 14 is made of an acrylic resin or the like, has a flat surface, and has a plurality of triangular projections 31 on the rear surface.
Are formed at a constant pitch. In this case, the interface between one side surface of the protrusion 31 and the air is a first optical interface 32, and the interface between the other side surface of the protrusion 31 and the air is a second optical interface 33. The interface between the back surface of the optical member 14 and the air between the projections 31 is a third optical interface 34. And the optical member 1
Numeral 4 is arranged on the light guide 15 with the apex of the protruding portion 31 approaching or in contact with the reflection film 24. In this state, the angle of the first optical interface 32 with respect to the step surface 22 of the light guide 15 (the angle of the first optical interface 32 on the side facing the step surface 23) is 90 ° or less, and the step surface 23
The surface is substantially parallel to or an inclined surface close thereto. The second optical interface 33 is an inclined surface whose angle with respect to a perpendicular to the surface of the optical member 14 is larger than the angle between the perpendicular and the first optical interface 32. The third optical interface 34 is a surface substantially parallel to the step surface 22 of the light guide 15 or an inclined surface close thereto. Note that the pitch of the projecting portions 31 of the optical member 14 is substantially the same as the pixel pitch of the liquid crystal display panel 1 or is a fraction of the pixel pitch. Further, the pitch of the step surface 22 of the light guide 15 is slightly larger than the pitch of the protruding portions 31 of the optical member 14.

The light diffusion layer 13 is formed by applying a transparent adhesive in which light scattering fine particles are dispersed on the surface of the optical member 14, for example. And the optical sheet 12
It is attached to the surface of the optical member 14 via the light diffusion layer 13. The liquid crystal display panel 1 is attached to the surface of the optical sheet 12 via a transparent adhesive or a double-sided adhesive sheet 35. As shown in FIG. 3, the optical sheet 12 has a transmission axis P and a reflection axis S that are substantially orthogonal to each other.
And transmits light of a polarization component (P polarization component) along the transmission axis P, and a polarization component (S polarization component) along the reflection axis S.
Light is reflected. That is, when light including both the P-polarized light component along the transmission axis P and the S-polarized light component along the reflection axis S is incident from the back surface side of the optical sheet 12, the incident light The light of the P polarization component along the transmission axis P is transmitted through the optical sheet 12, and the light of the S polarization component along the reflection axis S is reflected by the optical sheet 12.
Such a semi-transmissive and semi-reflective characteristic is the same for incident light from the surface side of the optical sheet 12.

When the liquid crystal display device is used as a transmission type, the fluorescent tube 17 is turned on. Then, the light from the fluorescent tube 17 and the reflected light reflected by the reflector 18 are incident on the light incident surface 21 of the light guide 15. The incident light is reflected by the reflection film 24 and the reflection plate 25 while being reflected by the light guide 1 as shown by a solid arrow in FIG. 2, for example.
5 travels in the horizontal direction, and is emitted from each step surface (light emitting surface) 23. The outgoing light is also applied to the first optical interface 32 of the optical member 14 as shown by the solid arrow in FIG.
And is totally reflected by the second optical interface 33, exits from the surface of the optical member 14, enters the light scattering layer 13 and is scattered. Of the scattered light, the light of the P-polarized component passes through the optical sheet 12 and is incident on the back surface of the liquid crystal display panel 1, and the light of the S-polarized component is reflected by the optical sheet 12. However, the light reflected by the optical sheet 12 is reflected by the reflection film 24 and is scattered again by the light scattering layer 13. Of the scattered light, the light of the P-polarized component passes through the optical sheet 12 and is incident on the back surface of the liquid crystal display panel 1, and the light of the S-polarized component is reflected by the optical sheet 12. By repeating such a process, most of the light emitted from each step surface 23 is incident on the back surface of the liquid crystal display panel 1. Note that the transmission axis of the optical sheet 12 and the transmission axis of the polarizing plate 6 on the back side of the liquid crystal display panel 1 are substantially parallel to each other. Then, the light incident on the back surface of the liquid crystal display panel 1 passes through the liquid crystal display panel 1 and is emitted to the front surface side of the liquid crystal display panel 1, whereby display is performed.

On the other hand, when the liquid crystal display device is used as a reflection type, external light is used without turning on the fluorescent tube 17. That is, external light (linearly polarized light) incident from the surface side of the liquid crystal display panel 1 is
Through. The transmitted light is transmitted through the optical sheet 12, the light diffusion layer 13 and the optical member 14 in order, as shown by a dotted arrow in FIG.
This reflected light passes through the optical member 14 and is diffused by the light diffusion layer 13. Most of the diffused light passes through the optical sheet 12 and is transmitted through the liquid crystal display panel 1 in the same manner as described above.
Is incident on the back surface of. This incident light is transmitted to the liquid crystal display panel 1
And is emitted to the front side of the liquid crystal display panel 1 to perform display.

Next, in this liquid crystal display device, the light source 1
A case in which display is performed by simultaneously using both the light from the light source 6 and the external light will be described. By the way, the suitable screen luminance of the liquid crystal display panel 1 (the luminance at which the display can be observed with sufficient brightness under the use environment) differs depending on the illuminance of the use environment (hereinafter referred to as environment illuminance). ,
Depending on the ambient illumination, the screen may be too dazzling or too dark. For example, under a high illuminance use environment exceeding 100,000 lux, such as under direct sunlight in summer, it will be too dazzling.

Therefore, in this liquid crystal display device, in order to obtain a suitable screen luminance that is not excessively dazzling even in a use environment of high illuminance exceeding 100,000 lux, such as in direct sunlight in summer, the liquid crystal display device is mainly provided with a reflective surface. The reflectance of the entire device determined by the reflectance of external light by the film 24 and the transmittance of light of the liquid crystal display panel 1 (the intensity of external light incident from the surface side of the liquid crystal display panel 1 and the reflection by the reflective film 24 (Ratio with the intensity of external light emitted to the front side of the liquid crystal display panel 1)
Is set lower than that of a normal reflective liquid crystal display device using only external light.

Further, by controlling the brightness of the light from the light source 16 in accordance with the ambient illuminance, the screen brightness of the liquid crystal display panel 1 due to both the light from the light source 16 and the external light is preferably adjusted in accordance with the environmental illuminance. The screen brightness is set. That is, in this liquid crystal display device, the light source 16
Light source control means (light emission control means) 41 is provided to control the brightness of light from the light source. Light source control means 41
Is an illuminance detection sensor 42 for detecting environmental illuminance, and means for controlling the luminance of light from the light source 16 based on the environmental illuminance detected by the illuminance detection sensor 42 (light source luminance adjusting unit 43 and light source driving unit 44) It consists of

The illuminance detection sensor 42 has a light receiving surface substantially parallel to the surface of the liquid crystal display panel 1 in order to measure the same environmental illuminance as the illuminance of external light incident on the surface of the liquid crystal display panel 1. It is arranged near the liquid crystal display panel 1. The light source luminance adjustment unit 43 changes the luminance value of the light from the light source 16 based on the environmental illuminance detected by the illuminance detection sensor 42, and sets the screen luminance of the liquid crystal display panel 1 to a predetermined luminance according to the environmental illuminance. It is adjusted to be within the range. The light source driving unit 44 drives the fluorescent tube 17 so that the fluorescent tube 17 emits light having a luminance corresponding to the luminance value from the light source luminance adjusting unit 43.

Next, the control of the brightness of the light from the light source 16 by the light source control means 41 in accordance with the ambient illuminance will be described with specific numerical values. First, FIG. 4 shows the relationship between the screen luminance of the liquid crystal display panel 1 and the environmental illuminance in this case. As a prerequisite, a suitable screen luminance of the liquid crystal display panel 1 according to the environmental illuminance is 20 to 200 nits at an ambient illuminance of 50 lux such as under a street lamp at night, such as in a room when indoor lighting is turned on. 1000
Lux ambient illuminance is 30-300 nits, and 30000 lux ambient illuminance such as shade of trees in fine weather is 400-4
000 nits, more preferably 20 to 60 nits at 50 lux environmental illuminance, 60 to 200 nits at 1000 lux environmental illuminance, and 1000 to 3000 nits at 30,000 lux environmental illuminance.

Now, the screen luminance L (nit) of the liquid crystal display panel 1 is I (lux) for the environmental illuminance, B (nit) for the luminance of light from the light source 16, and T for the light transmittance of the liquid crystal display panel 1. (%), The reflectance of the above-described device as a whole is R (%)
Is obtained from the following equation (1). L = I × R / 400 + B × T / 100 (1)

Therefore, first, the screen luminance L of the liquid crystal display panel 1 is 20 to 200 nits at an environmental illuminance of 50 lux, 30 to 300 nits at an environmental illuminance of 1000 lux,
The luminance of the light from the light source 16 is controlled by the light source control means according to the environmental illuminance so that the luminance represented by a quadratic function satisfying the range of 400 to 4000 nits at the environmental illuminance of 30,000 lux, respectively. That is, the control condition of the luminance of the light from the light source 16 in this case is obtained from the above equation (1), and is as shown in the following equation (2). −2 × 10 ⁻⁸ × I ² + 0.015 × I + 20 ≦ L ≦ −3 × 10 ⁻⁷ × I ² + 0.113 × I + 150 ... (2)

In FIG. 4, curves M ₁ and M ₂ show the maximum and minimum values of the screen luminance L obtained from the above equation (2). That is, the curves M ₁ and M ₂ are expressed by the following equation (3):
It is a curve respectively represented by (4). L (M ₁ ) = − 3 × 10 ⁻⁷ × I ² + 0.113 × I + 150 (3) L (M ₂ ) = − 2 × 10 ⁻⁸ × I ² + 0.015 × I + 20 (4) The range M between the two curves M ₁ and M ₂ is a range of a suitable screen luminance of the liquid crystal display panel 1 according to the environmental illuminance.

Next, second, the screen luminance L of the liquid crystal display panel 1 is set to 20 to 60 nits at an environmental illuminance of 50 lux.
60-200 nits at 300 lux lux, 300
The light source control means controls the luminance of the light from the light source 16 according to the environmental illuminance so that the luminance represented by a quadratic function that satisfies the range of 1000 to 3000 nits at the environmental illuminance of 00 lux. That is, the control condition of the luminance of the light from the light source 16 in this case is obtained from the above equation (1), and is as shown in the following equation (5). −9 × 10 ⁻⁸ × I ² + 0.0453 × I + 20 ≦ L ≦ −2 × 10 ⁻⁷ × I ² + 0.0871 × I + 50 ... (5)

In FIG. 4, curves N ₁ and N ₂ indicate the maximum and minimum values of the screen luminance L obtained from the above equation (5). That is, the curves N ₁ and N ₂ are given by the following equation (6):
It is a curve respectively represented by (7). L (N ₁ ) = − 2 × 10 ⁻⁷ × I ² + 0.0871 × I + 50 (6) L (N ₂ ) = − 9 × 10 ⁻⁸ × I ² + 0.0453 × I + 20 (7) The range N between the two curves N ₁ and N ₂ is a more preferable range of the screen luminance of the liquid crystal display panel 1 according to the environmental illuminance.

As described above, in this liquid crystal display device, the luminance of the light from the light source 16 is controlled by the light source control means 41 in accordance with the ambient illuminance, so that the screen luminance of the liquid crystal display panel 1 is represented by the curves M ₁ and M ₁ . A range M between the _two , more preferably a range N between the curves N ₁ and N ₂ . This allows
The screen brightness of the liquid crystal display panel 1 can be made favorable or more favorable in a wide range of environmental illuminance from low illuminance to high illuminance.

The two-dot chain line in FIG. 4 represents, for comparison, the screen luminance of a normal reflection type liquid crystal display device using only external light. The screen luminance indicated by the two-dot chain line changes linearly with the change in environmental illuminance. Then, in this conventional reflection type liquid crystal display device, ambient illuminance corresponding to the range M between curves M _1, M ₂ ranges from about 300 to about 5000 lux, the range between the curve N _1, N ₂ N
Is in the range of about 500 to about 2000 lux. Therefore, at a higher ambient illuminance, the screen of the liquid crystal display panel becomes too bright, and for example, under a high illuminance of more than 100,000 lux such as under direct sunlight in summer, the screen of the liquid crystal display panel becomes too dazzling. The display becomes difficult to see. On the other hand, if the ambient illumination is lower than that,
The screen of the liquid crystal display panel becomes too dark, and, for example, in a dark use environment such as outdoors at night, it is not possible to obtain a screen luminance enough to make the display visible.

Next, FIG. 5 shows a calculation relationship between the screen luminance of the liquid crystal display panel 1 and the environmental illuminance by only the light from the light source 16. As a precondition, first, the range of the environmental illuminance in which the screen luminance satisfying the above equation (2) is obtained using only the light from the light source 16 is 0 to about 120,000.
Secondly, the range of the ambient illuminance at which the screen luminance satisfying the above expression (5) is obtained using only the light from the light source 16 is 0 to about 63000 lux.

First, in FIG. 5, the curves M ₁₁ and M ₂₂ represent the maximum value (M _{1 in} FIG. 4) and the minimum value (M _{2 in} FIG. 4) of the screen luminance obtained by the above equation (2). ) Are curves respectively representing the screen luminance by only the light from the light source 16 for obtaining). Therefore, the screen brightness by only the light from the light source 16 for obtaining the screen brightness that satisfies the above equation (2) is in the range between these two curves M ₁₁ and M ₂₂ . Note that, in calculation, as shown in FIG.
Becomes more than lux screen brightness represented by the curve M ₂₂ 0
Since the light is emitted from the light source 16, the screen luminance does not become 0 nit or less. Therefore, at an ambient illuminance of about 300 lux or more, the above equation (2)
Screen brightness by only the light from the light source 16 for obtaining a screen brightness that satisfies is the range higher than or less 0 knitted screen brightness represented by curve M _11.

Second, in FIG. 5, the curves N ₁₁ and N ₂₂ represent the maximum value (N _{1 in} FIG. 4) and the minimum value (N _{2 in} FIG. 4) of the screen luminance obtained by the above equation (5). Light source 16 to obtain
7 are curves respectively representing the screen luminance by only the light from. Therefore, the screen brightness by only the light from the light source 16 for obtaining a screen brightness that satisfies the above expression (5) is in the range between the two curves N _11, N _22. In this case as well, the calculation shows that the environmental illuminance is about 800, as shown in FIG.
It becomes more than lux screen brightness represented by curve N ₂₂ 0
Since the light is emitted from the light source 16, the screen luminance does not become 0 nit or less. Therefore, also in this case, at an environment illumination of about 800 lux or more,
Light source 16 for obtaining a screen luminance satisfying the above equation (5)
Screen brightness by only the light from a range higher than or less 0 knitted screen brightness represented by curve N _11.

By the way, as an example, as it is apparent from FIG. 5, when the environmental illuminance is 1000 lux (about room illumination when is lit room lighting) above, screen brightness represented by the curve M ₂₂ and curve N ₂₂ Are less than or equal to 0 nits. Therefore, when the ambient illuminance is 1000 lux or more, even if the light source 16 is turned off, it is possible to obtain a screen luminance that satisfies the expressions (2) and (5). on the other hand,
As is clear from FIG. 4, when the environmental illuminance is 1000 lux or less, if the screen luminance is 80 to 150 nits, a suitable screen luminance can be obtained. Therefore, when the brightness of the light from the light source 16 is set to 100 nits, when the ambient illuminance is 1000 lux or less, the environmental illuminance increases and the amount of light reflected by the reflective film 24 shown in FIG. Brightness.
As a result, the environmental illuminance is detected by the illuminance detection sensor 42,
Based on this detection result, a suitable screen luminance can be obtained even if the light source 16 is turned off when the environmental illuminance is 1000 lux or more, and the light source 16 is turned on when the environmental illuminance is less than 1000 lux. Next, control of the light source 16 in such a case will be described.

FIG. 6 schematically shows the circuit configuration of the light source control means 41 in this case. This light source control means 41
Has a CPU 51. The CPU 51 is connected to each unit through a bus line 52 such as a data bus. The ROM 53 is a memory in which a program for performing circuit control is written. The RAM 54 temporarily stores data as described later. The sensor input unit 55 receives and processes a light detection signal output from the illuminance detection sensor 42 and outputs light detection data corresponding to the signal. The light source driving unit 44 drives the light source 16.

The sensor input unit 55 outputs light detection data corresponding to the light detection signal detected by the illuminance detection sensor 42, for example, every 0.5 seconds. The output light detection data is sent to the RAM 54 and is temporarily stored. RA
The M54, are four optical detection data X ₁ to X ₄ may temporarily store up to the previous before before several times for example 4 times than this. The CPU 51 determines each difference (X ₂ −X ₁ , X ₃ −X ₂ , X ₃ −X _{2) of} the _five light detection data X _{1 to} X ₅ four times before and this time.
X ₄ −X ₃ , X ₅ −X ₄ ) are calculated. If the first of the differences is negative and the subsequent ones are not positive, the environmental illuminance has decreased continuously, and the CPU 51 determines that the environmental illuminance has decreased. If the first of the above differences is positive and the subsequent ones are not negative, the environmental illuminance has increased continuously, and the CPU 51 determines that the environmental illuminance has increased.
In cases other than these two, for example, when the above-mentioned respective differences are all 0, or when the first of the above-mentioned differences is minus or plus, there is plus or minus thereafter, the CPU 51 Determines that the environmental illuminance has not changed.

Next, a case where the CPU 51 determines that the environmental illuminance has decreased will be described. The CPU 51
If it is determined that the environmental illuminance has decreased, then the RAM 54
Of light detection data X _{1 to} X ₅ temporarily stored in the
First photodetection data X ₁ is thereby determined whether a 1000 lux, the second light detection data X ₂ is equal to or less than 1000 lux of.
As an example, first, five light detection data X _{1 to} X ₅ are 9
If the data is equivalent to 00, 700, 700, 700, and 700 lux, it is determined that the environmental illuminance has decreased, but the first light detection data X ₁ is ₁ at 900 lux.
Since it is less than 000 lux, it is determined that the current state is maintained, and the light source 16 continues to be lit. Second, 5
One of the light detection data X ₁ to X ₅ is 2000,1500,15
When the data corresponding to 00,1500,1500 lux, although environmental illuminance is judged to have lowered, the second light detection data X ₂ is 1000 lux or more at 1500 lux, determines that the status quo As a result, the light source 16 is kept turned off. Third, five optical detection data X ₁ to X ₅ is 2000,700,700,700,
When the data corresponding to 700 lux, the environment illumination intensity is determined to be decreased, and it is the first light detection data X ₁ is 1000 lux or more at 2000 lux, 2
Th the light detection data X ₂ is less than 1000 lux at 700 lux, it is determined that the light source lighting, as shown in FIG. 7 (A), so that the light source 16 is turned on by the light source drive unit 44. In this case, at time t ₂ when the light detection data X ₁ has elapsed from the time t ₁ that is detected 2.5 seconds, the light source 16 is turned on.

Next, a case where the CPU 51 determines that the environmental illuminance has increased will be described. The CPU 51
If it is determined that the environmental illuminance has increased, then the RAM 54
Of light detection data X _{1 to} X ₅ temporarily stored in the
First photodetection data X ₁ is thereby determined whether less than 1000 lux, the second light detection data X ₂ is equal to or 1000 lux or more of.
As an example, first, five light detection data X _{1 to} X ₅ are 7
If the data is equivalent to 00, 900, 900, 900, and 900 lux, it is determined that the environmental illuminance has increased, but the second light detection data X ₂ is 1 at 900 lux.
Since it is less than 000 lux, it is determined that the current state is maintained, and the light source 16 continues to be lit. Second, 5
One of the light detection data X ₁ to X ₅ is 1500,2000,20
When the data corresponding to 00,2000,2000 lux, although environmental illuminance is judged to have increased, since the first light detection data X ₁ is at 1000 lux or more at 1500 lux, determines that the status quo As a result, the light source 16 is kept turned off. Third, the five light detection data X _{1 to} X ₅ are 700, 2000, 2000, 200
If the data is equivalent to 0, 2000 lux,
Environment illuminance is determined to be increased, and the first light detection data X ₁ is less than 1000 lux at 700 lux, 10 second light detection data X ₂ are at 2000 lux
Since the light source is 00 lux or more, it is determined that the light source is turned off.
As shown in (B), the light source 16 is turned off by the light source driving unit 44. In this case, at time t ₂ when the light detection data X ₁ has elapsed from the time t ₁ that is detected 2.5 seconds, the light source 16 is turned off.

Next, a case where the CPU 51 determines that the environmental illuminance has not changed will be described. First, when each of the differences (X ₂ −X ₁ , X ₃ −X ₂ , X ₄ −X ₃ , X ₅ −X ₄ ) is 0, the ambient illuminance naturally changes. It is determined that there is not. Then, next, the case where the first one of the above differences is minus or plus, followed by plus or minus will be described. As an example, five light detection data X _{1 to} X ₅ are 20
It is assumed that the data is equivalent to 00, 700, 700, 700, and 2000 lux. Then, each difference (X ₂ −
X ₁ , X ₃ -X ₂ , X ₄ -X ₃ , X ₅ -X ₄ ) are −130
0, ± 0, ± 0, +1300. This is the case where the first of the above-mentioned differences is minus, but there is a plus thereafter. In such a case, the CPU 51 determines that the environmental illuminance has not changed. Therefore,
For example, when a train passes through an iron bridge during the day even if the environmental illuminance alternates between an illuminance higher than 1000 lux and a low illuminance in a short time within 0.5 seconds x 5 = 2.5 seconds. Even if sunlight is interrupted intermittently by the iron bridge,
Determines that the environmental illuminance has not changed and maintains the current state. As a result, even if the ambient illuminance alternates around 1000 lux in a short time, the light source 16 does not blink and the screen can be prevented from flickering.

In the above description, FIGS. 7A and 7B
As shown in ( ₂ ), the light source 16 is completely turned on or off at the time t2, but the present invention is not limited to this. For example, as shown in FIG. 8 (A), gradually increasing the luminance of the emitted light starts the emission of light from the light source 16 at the time of t _2, the luminance of the emitted light at the time of t ₃ You may make it 100 nits. Further, as shown in FIG. 8 (B), the light source 16 from the time point of t ₂
Gradually lowering the luminance of light from, may be completely turning off the light source 16 at the time of t _3.

When the surroundings gradually become darker or brighter, the arrangement may be as shown in FIGS. 9 and 10, respectively. In this case, as is apparent from FIG. 4, when the screen luminance is 100 nits, the ambient illuminance of about 600 to 2,000 lux is a more suitable environmental illuminance range N, for example. Therefore, a good environmental illuminance range is set to 600 to 2
000 lux, the lower limit is 600 lux, and the upper limit is 2000 lux.

[0035] Then, as shown in FIG. 9 (A), circumference gradually darker, when the environmental illuminance is lower than the upper limit value 2000 lux good environmental illuminance range at the time of t _1, for example, the Each difference (X ₂ −X ₁ , X ₃ −X ₂ , X ₄ −
X ₃ , X ₅ −X ₄ ) are all negative and their absolute values are relatively small, and as shown in FIG.
At the time of ₂ to gradually increase the brightness of the emitted light starts the emission of light from the light source 16, the intensity of the emitted light 100 knit at the time of t _3. On the other hand, as shown in FIG.
If the environmental illuminance is higher than the lower limit value 600 lux good environmental illuminance range at the time of t _1, for example, each of the difference _{(X 2 -X 1, X 3} -X 2, X 4 -X 3, X 5 −X ₄ ) are all positive and their values are relatively small.
As shown in FIG. 0 (B), the brightness of the light from the light source 16 is gradually reduced from the time point t ₂ , and the light source 1 at the time point t _3.
Turn off 6 completely.

When the surroundings suddenly become dark or bright, the arrangement may be as shown in FIGS. 11 and 12, respectively. That is, as shown in FIG.
Ambient becomes suddenly darkened, when the environmental illuminance is lower than the upper limit value 2000 lux good environmental illuminance range at the time of t _1, for example, each of the difference _{(X 2 -X 1, X 3} -X 2, X
_{Based on the fact that 4-} X ₃ and X ₅ -X ₄ ) are all negative and their absolute values are relatively large, as shown in FIG. 11B, the light emission from the light source 16 is stopped at the time t _2. At the start, the brightness of the emitted light is gradually increased (however, FIG.
(Abruptly than in the case of (B)), and the luminance of the emitted light is set to 100 nits at the time point of t ₃ . On the other hand, FIG.
(A), the periphery becomes suddenly bright, the lower limit of the environmental illuminance good environmental illuminance range at the time of t ₁ 6
If the lux is higher than 00 lux, for example, the difference (X
₁₂₋ X ₁ , X ₃ −X ₂ , X ₄ −X ₃ , X ₅ −X ₄ ) are all positive and their values are relatively large.
(B), the completely turning off the light source 16 at the time of t _2.

By the way, in the case shown in FIG.
completely off the light source 16 at the time of t _2, FIG. 11
In the case shown in (B), although gradually increase the brightness of the emitted light starts the emission of light from the light source 16 at the time of t _2, it will now be described why. When the surroundings suddenly become brighter, the brightness of the external light is considerably larger than the brightness of the light from the light source 16.
Even if the brightness of the light from is adjusted, the brightness of the screen itself does not change so much. Therefore, as shown in FIG.
Power can be saved. On the other hand, when the surroundings become suddenly dark, when fully lights the light source 16 at the time of t _2, since it is felt that the screen becomes too bright without familiar eyes, as shown in FIG. 11 (B) Then, the eyes can be reduced.

In the above description, the case where the fluorescent tube 17 is used has been described. However, the present invention is not limited to this, and a linear light emitting diode array or the like may be used. In the above description, the case where the present invention is applied to a liquid crystal display device has been described. However, the present invention is not limited to this, and can be applied to a display device having another non-light emitting type display panel.

[0039]

As described above, according to the present invention, when the light emission control means controls the light emission of the reflection and light emission means based on the change of the environmental illuminance within a preset time, the environment When the illuminance alternates between an illuminance higher and a illuminance lower than a preset illuminance within a preset time, if the light emission control unit ignores the illuminance, the environmental illuminance becomes the preset illuminance. Even if the illuminance is higher and lower than the illuminance alternately in a short time, the screen of the display panel can be prevented from flickering.

[Brief description of the drawings]

FIG. 1 is a side view of a main part of a liquid crystal display device to which an embodiment of the present invention is applied.

FIG. 2 is a diagram illustrating the progress of light in a part of a liquid crystal display device.

FIG. 3 is a perspective view illustrating an optical sheet.

FIG. 4 is a diagram showing a relationship between screen luminance of a liquid crystal display panel and environmental illuminance.

FIG. 5 is a view showing a calculation relationship between screen luminance of a liquid crystal display panel and environmental illuminance only by light from a light source.

FIG. 6 is a schematic diagram of a circuit configuration of a light source control unit.

FIG. 7 is a view for explaining an example of light source control.

FIG. 8 is a view for explaining another example of light source control.

FIG. 9 is a diagram illustrating an example of light source control when the surroundings gradually darken.

FIG. 10 is a diagram illustrating an example of light source control when the surroundings gradually become brighter.

FIG. 11 is a diagram illustrating an example of light source control when the surroundings suddenly darken.

FIG. 12 is a diagram illustrating an example of light source control when the surroundings suddenly become bright.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal display panel 11 Backlight 16 Light source 17 Fluorescent tube 41 Light source control means 42 Illuminance detection sensor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H091 FA14Z FA23Z FA31Z FA42Z FA45Z FB02 FB06 FB08 FC02 FD06 GA11 LA16 2H093 NA06 NC45 NC55 ND10 NE06 NF03 5G435 AA00 BB12 BB15 BB16 DD13 EE30 EE33 FF03 FF24

Claims (7)

[Claims] 1. A non-light-emitting display panel, disposed on a back side of the display panel, emitting light toward the back side of the display panel, and being incident on the front side of the display panel to receive light. Reflection and light emitting means for reflecting external light transmitted through the display panel toward the back surface of the display panel, and calculating a change in environmental illuminance within a preset time by detecting environmental illuminance, and based on the calculation result, A display device comprising: a light emission control means for controlling light emission of the reflection and light emission means. 2. The light emission control means according to claim 1, wherein the light emission control means is configured to output the light from the reflection and light emission means when the environmental illuminance continuously becomes higher than a preset illuminance within a preset time. Control to stop the emission of light of
A display device which controls so as to start emitting light from the reflection / light emitting means when the temperature continuously decreases. 3. The invention according to claim 1, wherein the light emission control means is configured to control the reflection when the environmental illuminance continuously becomes higher than a lower limit value of a preset illuminance range within a preset time. It is controlled to stop the emission of light from the combined light emitting means, and to control the emission of the light from the reflection and light emitting means to start when the light is continuously lower than the upper limit of the same illuminance range. Characteristic display device. 4. The light emission control means according to claim 1, wherein the light emission control means is configured to perform the reflection and light emission when the environmental illuminance continuously and gradually becomes higher than a preset illuminance within a preset time. The luminance of the light from the means is controlled to be gradually lowered to finally stop the light emission, and when the light is continuously reduced gradually, the light emission from the reflection / light emission means is started and the light emission is started. A display device, wherein the luminance of emitted light is controlled so as to gradually increase. 5. The light emitting control device according to claim 1, wherein the light emission control means determines that the ambient illuminance is gradually increased within a preset time from a lower limit of a preset illuminance range. Control to gradually lower the brightness of the light from the reflection and light emission means and finally stop the emission of light,
When the light intensity becomes lower continuously than the upper limit of the same illuminance range, light emission from the reflection / light emission means is started and the luminance of the emitted light is controlled so as to gradually increase. Display device. 6. The light emission control means according to claim 1, wherein the light emission control means is configured to output the reflected and light when the ambient illuminance continuously and suddenly becomes higher than a preset illuminance within a preset time. The emission of the light from the means is controlled so as to be stopped immediately, and when it continuously drops suddenly, the emission of the light from the reflection and light emission means is started and the luminance of the emitted light is gradually increased. A display device characterized by controlling. 7. The light emitting control device according to claim 1, wherein the light emission control means determines that the ambient illuminance suddenly becomes higher than a lower limit value of a preset illuminance range within a preset time. Controlling the emission of light from the reflection and light emission means to be stopped immediately, and when the light emission from the reflection and light emission means is started when it suddenly becomes lower than the upper limit of the same illuminance range, the light emission is started. A display device wherein the luminance of the emitted light is controlled so as to gradually increase.