JP2002182199A - Backlight device - Google Patents

Abstract

(57) [Problem] To provide a backlight device having high light use efficiency both when used as a backlight and also when used as a reflector. SOLUTION: A reflective polarizing plate 1 is provided on the back side of a liquid crystal display element 1.
4 between the light guide member 15 and the reflective plate 17 disposed on the back side of the reflective polarizer 14,
It is possible to switch between a liquid crystal molecule alignment state in which a phase difference is generated by causing a phase difference corresponding to (1/4) wavelength to change a polarization state and a liquid crystal molecule alignment state in which a phase difference is not generated with respect to transmitted light in accordance with application of a voltage. A polarization conversion liquid crystal cell 21 was provided.
Therefore, the polarization conversion liquid crystal cell 21 can be used as a (1/4) λ plate, and can also be used as a light-transmitting member having no phase difference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device for a display device which also serves as a light reflecting means, and more particularly to a backlight device suitable for a liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, in a liquid crystal display device, as shown in FIG. 5, the back side of the liquid crystal display device 1 is illuminated by a backlight device 2 so that information such as an image displayed on the liquid crystal display device 1 is displayed. Can be seen even in dark places. The liquid crystal display element 1 of such a liquid crystal display device includes a liquid crystal cell 3 for display, an upper polarizing plate 4 is provided on an upper surface of the liquid crystal cell 3, and a lower polarizing plate 5 is provided on a lower surface of the liquid crystal cell 3. It has a structure. This display liquid crystal cell 3
Are provided on the opposing surfaces of a pair of upper and lower transparent substrates 6 and 7, respectively.
For example, in the case of a simple matrix type, a plurality of transparent electrodes 8 and 9 made of TO or the like are provided in rows and columns, respectively, and the alignment films 1 and 9 cover the electrodes 8 and 9.
0 and 11 are provided, and the pair of substrates 6 and 7 are formed into a frame-shaped sealing material 1 in a state where the alignment films 10 and 11 are vertically opposed to each other.
2 and a liquid crystal 13 is sealed in a region surrounded by the sealing material 12 and the pair of substrates 6 and 7.

In this case, as shown in FIG. 6, in the case of a so-called TN type liquid crystal display element, the alignment films 10 and 11 opposed to the upper and lower sides of the liquid crystal cell 3 are subjected to alignment processing in directions substantially orthogonal to each other. . That is, in FIG. 6, the arrow A indicates the alignment direction of the liquid crystal molecules approaching the alignment film 11 of the lower substrate 7 (that is, the same direction as the alignment processing direction of the alignment film 11), and the arrow B indicates the alignment film of the upper substrate 6. Orientation direction of the liquid crystal molecules approaching 10 (that is, the same direction as the orientation processing direction of the orientation film 10)
Is shown. As a result, the molecules of the liquid crystal 13 are twist-oriented between the pair of upper and lower substrates 6 and 7 at a twist angle of approximately 90 ° clockwise as viewed from above the liquid crystal display element 1. The upper polarizing plate 4 is disposed such that its transmission axis 4a is substantially perpendicular to the alignment processing direction B of the upper substrate 6 of the liquid crystal cell 3. The lower polarizing plate 5 has its transmission axis 5a.
a is arranged in a state substantially orthogonal to the alignment processing direction A of the lower substrate 7 of the liquid crystal cell 3.

As shown in FIG. 5, a backlight device 2 for illuminating the rear side of the liquid crystal display element 1 has a reflective polarizing plate 14 facing the rear surface of the liquid crystal display element 1, ie, the lower surface of the lower polarizing plate 5, as shown in FIG. A light guide member 15 facing the lower surface of the reflective polarizer 14, a retarder 16 facing the lower surface of the light guide member 15, and a reflector 17 facing the lower surface of the retarder 16 from above. The light source 18 is arranged in order, and the light source 18 is arranged on one end face side of the light guide member 15. In this case, as shown in FIG. 6, the reflective polarizing plate 14 has a reflection axis 14a for reflecting light of one polarization component orthogonal to the other and a transmission axis for transmitting light of the other polarization component orthogonal to the one polarization component. Axis 14b, the reflection axis 14a is substantially orthogonal to the transmission axis 5a of the lower polarizing plate 5 of the liquid crystal cell 3, and the transmission axis 14a
b is arranged so as to be substantially parallel to the transmission axis 5 a of the lower polarizing plate 5. The retardation plate 16 is a (1/4) λ (wavelength) plate, and its slow axis 16a intersects the reflection axis 14a and the transmission axis 14b of the reflective polarizer 14 at approximately 45 °. It is provided in.

When the backlight device 2 illuminates the liquid crystal display element 1 from the rear side, as shown in FIG. 7, when the light source 18 is turned on, the light from the light source 18 is transmitted to the light guide member 15. The introduced light is introduced into the light guide member 15.
Then, the light is emitted toward the lower polarizing plate 5 of the liquid crystal display element 1 through the reflective polarizing plate 14. At this time, the reflective polarizer 14
The polarized component light having a vibration plane along the transmission axis 14b (hereinafter referred to as polarized component light) is transmitted and emitted toward the lower polarizing plate 5, and the polarized component light along the reflection axis 14a is The light is reflected toward the retardation plate 16. This reflected light
When transmitted through the phase difference plate 16, the (1/4) λ phase shifts,
The light having the shifted phase is reflected by the reflection plate 17 and transmitted through the phase difference plate 16 again, so that the (1/4) λ phase is further shifted. Therefore, the light reflected by the reflective polarizing plate 14 is (1/1 /
4) By transmitting through the λ retardation plate 16 twice, (1/1)
2) The λ phase is shifted and the polarized component light in the direction of the reflection axis becomes the polarized component light in the direction of the transmission axis, thereby transmitting through the reflective polarizing plate 14 and being emitted toward the lower polarizing plate 5 of the liquid crystal display element 1. As described above, according to the backlight device 2, the liquid crystal display element 1 can be illuminated by efficiently using the light introduced from the light source 18 to the light guide member 15 while suppressing waste.

When the liquid crystal display element 1 is used as a reflection type, external light is taken in from the upper surface side of the liquid crystal display element 1 with the light source 18 turned off as shown in FIG. At this time, after the external component polarized light along the transmission axis 4a of the upper polarizing plate 4 is taken in and transmitted through the liquid crystal cell 3 for display, the polarized component light along the transmission axis 5a of the lower polarizing plate 5 is The light passes through the lower polarizer 5 and enters the reflective polarizer 14 of the backlight device 2. The light incident on the reflective polarizer 14 passes through the reflective polarizer 14 as shown in FIG. 8 because the transmission axis 14 of the reflective polarizer 14 is substantially parallel to the transmission axis 5a of the lower polarizer 5. Thereafter, the light passes through the light guide member 15 and enters the phase difference plate 16.

The light incident on the phase difference plate 16 as described above is
When transmitting the light, the (１ ／) λ phase is shifted, and the light having the shifted phase is reflected by the reflection plate 17 and is again reflected by the phase difference plate 16.
Is further shifted by (1/4) .lamda. When the light is transmitted, the transmitted light is shifted by 1 / 2.lamda. And becomes polarized component light along the reflection axis 14a of the reflective polarizing plate 14. FIG. For this reason, the light that has reciprocated through the retardation plate 16 once is reflected again by the reflection axis 14a of the reflection polarizing plate 14, and the reflected light repeats the same operation as described above to pass through the retardation plate 16 again. The light passes through one reciprocation, and further becomes (() λ shifted in phase to become polarized component light along the transmission axis 14b of the reflective polarizing plate 14. As described above, the light transmitted through the lower polarizer 5 and incident on the reflective polarizer 14 reciprocates through the phase difference plate 16 twice,
, And is incident on the lower polarizing plate 5 of the liquid crystal display element 1 again.

As a result, the backlight device 2
By functioning as a reflector and reflecting light emitted from the upper surface side of the liquid crystal display element 1 and emitted from the lower surface side, the light can be incident again on the lower surface side of the liquid crystal display element 1.
As described above, in the backlight device 2, the back side of the liquid crystal display element 1 can be illuminated by turning on the light source 18, and when the light source 18 is turned off, the liquid crystal display element 1 is turned to the reflection type. It also has a function as a reflector for displaying as a liquid crystal display element.

[0009]

However, when such a backlight device 2 is used as a reflection plate, the light transmitted through the liquid crystal display element 1 and incident upon the backlight device 2 as described above is reflected in the backlight device 2. Without reciprocating, the light cannot be incident on the liquid crystal display element 1 again. For this reason, in the backlight device 2, compared with the case where the transmitted light of the liquid crystal display element 1 is simply reflected by the reflection plate, the light loss is large, and the display of the liquid crystal display element 1 is performed when the display is performed in the reflection mode. There is a problem that becomes dark.

An object of the present invention is to provide a backlight device having high light use efficiency not only when used as an original backlight but also when used as a reflector.

[0011]

SUMMARY OF THE INVENTION The present invention relates to a backlight device provided on the back side of a display element, wherein the reflection axis is arranged to face the back side of the display element and reflects light of one polarization component. And a reflective polarizer having a transmission axis that transmits light of the other polarized component orthogonal to the one polarized component, and a reflective plate disposed on the surface of the reflective polarizer opposite to the display element, A light guide member disposed between the reflective polarizer and the reflective plate; and a light guide member disposed between the reflective polarizer and the reflective plate, and (1 + 2n) / 4 (where n is 0) for transmitted light. (Positive integer that includes a liquid crystal molecule) that causes a phase difference corresponding to the wavelength to change the polarization state, and a liquid crystal molecule alignment state that does not cause a phase difference with respect to transmitted light according to the application of voltage. A conversion liquid crystal cell,
A light source disposed on an end face side of the light guide member.

According to the present invention, the polarization conversion liquid crystal cell is made to function as a (1/4) λ retardation plate and the phase difference in response to the voltage (electric field) applied to the polarization conversion liquid crystal cell. Can be switched to the action of the light-transmitting member, which does not change.
For this reason, by making the polarization conversion liquid crystal cell function as a (1/4) λ retardation plate, light from the light source can be introduced into the light guide member and efficiently incident on the back side of the display element. In addition, by making the polarization conversion liquid crystal cell function as a light transmitting member that does not cause a phase difference, the light transmitted through the display element and emitted to the back side enters the polarization conversion liquid crystal cell and is transmitted therethrough. Since the light is transmitted and reflected by the reflection plate without generating a phase difference, the light can be transmitted through the reflection polarization plate and made incident on the back side of the display element by making one round trip of the polarization conversion liquid crystal cell. As a result, this backlight device has a reflection function of a high reflectance as a reflection plate of a display element, and is used for a liquid crystal display element to reduce light loss and improve light use efficiency as compared with the conventional example. Can be enhanced.

In this case, the liquid crystal cell for polarization conversion is a liquid crystal cell in which the liquid crystal molecules are homogeneously aligned, so that the liquid crystal molecules are homogeneously aligned when no electric field is applied. , (1 /
4) Used as a λ retardation plate, and used as a light-transmitting member that does not generate a phase difference because liquid crystal molecules are oriented almost perpendicular to a pair of substrates of a liquid crystal cell for polarization conversion when a voltage is applied. can do. In this case, the liquid crystal cell has a refractive index anisotropy Δ
The product Δn · d of n and the cell gap d is 138 ± 20 nm
It is desirable that

Further, the liquid crystal cell for polarization conversion is a liquid crystal cell in which liquid crystal molecules are twist-aligned, so that the liquid crystal molecules are twist-aligned when no electric field is applied. A light-transmissive member that is used as a phase difference plate that changes the phase difference, and that does not generate a phase difference when liquid crystal molecules are oriented almost perpendicular to a pair of substrates of a polarization conversion liquid crystal cell when an electric field is applied. Can be used as In this case, the liquid crystal cell has a twist angle of 63.7 °.
Where the refractive index anisotropy Δn is 0.03 and the cell gap d is 6
Preferably, it is 500 nm.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a backlight device according to the present invention will be described below with reference to FIGS. The same components as those in the conventional example shown in FIGS. The backlight device 20 is different from the conventional example in that the (1/4) λ phase difference plate 16 is replaced with
The liquid crystal cell 21 for polarization conversion is provided between the light guide member 15 and the reflection plate 17.

As shown in FIG. 1, this polarization conversion liquid crystal cell 21 has a single transparent flat electrode 24 made of ITO or the like over the entire opposing surfaces of a pair of upper and lower transparent substrates 22 and 23.
25, and alignment films 26 and 27 are provided to cover the electrodes 24 and 25.
A pair of substrates 22 and 2 are placed in a state where
3 are joined via a frame-shaped sealing material 28, a liquid crystal 29 is sealed in a region surrounded by the sealing material 28 and the pair of substrates 22, 23, and molecules of the liquid crystal 29 are homogeneously aligned. It has become.

That is, this polarization conversion liquid crystal cell 21
Means that the twist angle is 0 ° and the refractive index anisotropy Δn of the liquid crystal 29 is
Is 0.021 and the cell gap, that is, the liquid crystal layer thickness d is 65.
00n, product Δn of refractive index anisotropy Δn and liquid crystal layer thickness d
D is set to 138 ± 20 nm, and as shown in FIG. 2, the liquid crystal molecules are initially oriented in a direction 29 a crossing the reflection axis 14 a and the transmission axis 14 b of the reflective polarizer 14 at approximately 45 °. The alignment films 26 and 27 are subjected to an alignment process. Thereby, the polarization conversion liquid crystal cell 21
The liquid crystal molecules have the same function as the (1/4) λ plate because the liquid crystal molecules are homogeneously aligned when no voltage is applied to the electrodes 24 and 25, and when the voltage is applied, the liquid crystal molecules When the liquid crystal layer is oriented in a direction substantially perpendicular to the directions 22 and 23, the liquid crystal layer has almost no refractive index anisotropy, that is, Δn ≒ 0, so that a phase difference is hardly generated in transmitted light.

As described above, the polarization conversion liquid crystal cell 21 is
When no voltage is applied, the liquid crystal molecules are homogeneously aligned and have the same function as the (1/4) λ retardation plate, and when a voltage is applied, the liquid crystal molecules are oriented substantially perpendicular to the substrates 22 and 23. The liquid crystal cell 21 for polarization conversion has the function of a (1/4) λ retardation plate and the transparency which does not cause a phase difference in response to non-application / application of voltage. The function of the light plate is switched.

Therefore, in the backlight device 20, when the light source 18 is turned on and used as a surface light source, no voltage is applied to the polarization conversion liquid crystal cell 21 and the polarization conversion liquid crystal cell 21 1/4) function as a λ plate.
That is, as shown in FIG. 3, when the light source 18 is turned on, the light is introduced into the light guide member 15, and among the introduced light, the polarized component light along the transmission axis 14 b of the reflective polarizing plate 14 is converted. Is transmitted through the reflective polarizer 14 and is emitted toward the rear surface of the liquid crystal display device 1 as polarized component light along the transmission axis 5a of the lower polarizer 5, and the polarized component light along the reflective axis 14a is subjected to polarization conversion. To the liquid crystal cell 21 for use. When the reflected polarization component light passes through the polarization conversion liquid crystal cell 21, the phase is shifted by (１ ／) λ, and the light whose phase is shifted is reflected by the reflection plate 17 and is again reflected by the polarization conversion liquid crystal cell 21. 21 and further (1/4) λ phase shifts, so that it becomes polarized component light along the transmission axis 14b of the reflective polarizer 14,
The light passes through the reflective polarizer 14 and is emitted as light along the transmission axis 5 a of the lower polarizer 5 toward the back surface of the liquid crystal display element 1. For this reason, in the backlight device 20, similarly to the conventional example, the light introduced into the light guide member can be efficiently incident on the rear side of the liquid crystal display element 1 while suppressing loss.

When a backlight is used as a reflection plate, a voltage is applied to the polarization conversion liquid crystal cell 21 so that the polarization conversion liquid crystal cell 21 is used as a light transmitting plate having no phase difference. That is, as shown in FIG. 4, in a state where the light source 18 is turned off, external light is taken in from the upper surface side of the liquid crystal display element 1. At this time, similarly to the conventional example, of the external light, the polarized component light along the transmission axis 4a of the upper polarizing plate 4 is taken in and transmitted through the liquid crystal cell 3 for display.
The light is rotated (rotated) by 0 °, becomes polarized component light along the transmission axis 5 a of the lower polarizing plate 5, transmits through the lower polarizing plate 5, and enters the reflective polarizing plate 14 of the backlight device 20. This reflective polarizing plate 1
4 is incident on the transmission axis 1 of the reflective polarizer 14.
4b is substantially parallel to the transmission axis 5a of the lower polarizing plate 5,
As shown in FIG. 4, the reflective polarizing plate 14 and the light guide member 15
To enter the polarization conversion liquid crystal cell 21.

At this time, since a voltage is applied to the polarization conversion liquid crystal cell 21 so that the liquid crystal molecules are aligned in a direction perpendicular to the substrate, the light incident on the polarization conversion liquid crystal cell 21 has a phase difference. Liquid crystal cell 2 without polarization
1 and is reflected by the reflection plate 17, and the reflected light is reflected again without causing a phase difference.
Is transmitted through the liquid crystal cell 21 for polarization conversion, and the reflected light passes through the reflective polarizing plate 14 and stays under the rear surface of the liquid crystal display element 1 while maintaining the polarized component light along the transmission axis 14b of the reflective polarizing plate 14. The light enters the polarizing plate 5 and the polarized component light is transmitted through the transmission axis 5.
Since the light is polarized component light along a, the light passes through the lower polarizing plate 5. Thus, the backlight device 20 according to the present invention
Does not reciprocate light twice inside as in the prior art even when used as a reflector of the liquid crystal display element 1, so that light loss is small and light use efficiency can be improved. The display in the reflection mode 1 can be brightened.

In the above embodiment, the liquid crystal cell for polarization conversion has a twist angle of 0 °, a refractive index anisotropy Δn of the liquid crystal 29 of 0.021, and a cell gap d of 6500 n.
m, the product of the refractive index anisotropy Δn and the cell gap d, Δn ·
Although the case where the polarization conversion liquid crystal cell 21 in which d is 138 ± 20 nm is used has been described, the invention is not limited to this.
When the twist angle is 0 ° and the refractive index anisotropy Δn of the liquid crystal is 0.0
63, the cell gap d is 6500 nm, and the product Δn · d of the refractive index anisotropy Δn and the cell gap d is 414 ± 20.
A liquid crystal cell for polarization conversion having a wavelength of nm may be used. That is,
The polarization conversion liquid crystal cell has a Δnd value of (1 + 2n).
λ / 4 (where n is a positive integer including 0: 0, 1, 2)
It is.

Further, in the above-described embodiment, the case where the polarization conversion liquid crystal cell 21 in which liquid crystal molecules are homogeneously aligned is used as the polarization conversion liquid crystal cell, but the present invention is not limited to this. A polarized liquid crystal cell for polarization conversion may be used. Also in this case, the liquid crystal cell for polarization conversion has the same function as the (1/4) λ retardation plate because the liquid crystal molecules are twisted when no voltage is applied, and the voltage is applied. In some cases, the liquid crystal molecules are oriented in a direction substantially perpendicular to the pair of substrates 22 and 23, so that the refractive index anisotropy of the liquid crystal layer is almost eliminated, that is, Δn ≒ 0, and almost no phase difference occurs in the transmitted light. What is necessary is just to be comprised so that it may not be made.

As such a liquid crystal cell for polarization conversion,
The twist angle is 63.7 ° and the refractive index anisotropy Δn is 0.0
3, the cell gap d is 6500 nm, and the product Δn · d of the refractive index anisotropy Δn and the cell gap d is 0.03 × 65.
A liquid crystal cell of 00 = 195 nm is preferable, but not limited thereto. The twist angle is 190.1 °, the refractive index anisotropy Δn is 0.09, the cell gap d is 6500 nm, and the refractive index anisotropy Δn is The product Δn · d with the cell gap d is 0.09
× 6500 = a liquid crystal cell of 585 nm, or a twist angle of 318.2 °, a refractive index anisotropy Δn of 0.15, a cell gap d of 6500 nm, and a product of the refractive index anisotropy Δn and the cell gap d Δn · d is 0.15 × 6500 = 9
A 75 nm liquid crystal cell may be used.

The backlight device of the present invention is not limited to a backlight device for a liquid crystal display device, but is widely applied as a backlight device for various display devices requiring a predetermined polarization component light as incident light. be able to. Also,
In the above embodiment, the polarization conversion liquid crystal cell is disposed between the light guide member and the reflection plate, but is not limited thereto, and the polarization conversion liquid crystal cell may be disposed between the light guide member and the reflection polarization plate. The same effect as in the above embodiment can be obtained.

[0026]

As described above, according to the present invention, the reflective polarizer is disposed on the back side of the display element, and the light guide member is provided between the reflective polarizer and the reflective plate disposed on the rear side of the reflective polarizer. And a polarization conversion liquid crystal cell that changes the polarization state of the transmitted light according to the applied voltage.
The structure is such that it can be used as a (1/4) λ retardation plate and also as a light transmitting member whose phase difference does not change. Accordingly, when the backlight device of the present invention is used as a backlight of a transmission type display element, the liquid crystal cell for polarization conversion is used as a (1/4) λ retardation plate, and a light source from a light source is used as in the conventional example. The back side of the display element can be efficiently illuminated by effectively utilizing the light.
When the backlight device of the present invention is used as a reflection plate of a reflective display element, the polarization conversion liquid crystal cell 21 is used as a transmissive member having no phase difference, and the reflection polarization plate is used. Is transmitted through the polarization conversion liquid crystal cell without causing a phase difference and is reflected by the reflection plate without causing a phase difference, and the reflection polarization plate is formed by making one round trip of the polarization conversion liquid crystal cell. To be transmitted and incident on the back side of the display element. Thereby, even when used as a light reflecting means of the display element, compared to the conventional example,
Light loss is small and light use efficiency can be increased.

In this case, the liquid crystal cell for polarization conversion is a liquid crystal cell in which liquid crystal molecules are homogeneously aligned, and the liquid crystal molecules are homogeneously aligned when no electric field is applied. Used as a board,
Further, when an electric field is applied, the liquid crystal molecules are aligned in a direction substantially perpendicular to the pair of substrates of the polarization conversion liquid crystal cell, so that the liquid crystal cell can be used as a light transmitting member having no phase difference. In addition, the liquid crystal cell for polarization conversion is a liquid crystal cell in which liquid crystal molecules are twist-aligned, so that the liquid crystal molecules are twist-aligned when no electric field is applied.
It is used as a (1/4) λ retardation plate, and when an electric field is applied, the liquid crystal molecules are oriented in a direction substantially perpendicular to a pair of substrates of the polarization conversion liquid crystal cell, so that a phase difference is not generated. It can be used as an optical member.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an embodiment in which a backlight device of the present invention is arranged on a lower surface side of a liquid crystal display element.

FIG. 2 is a diagram illustrating optical axes of respective members in FIG. 1;

FIG. 3 is a diagram showing a traveling state of light when illuminating a liquid crystal display element with the backlight device of FIG. 1;

FIG. 4 is a diagram showing a traveling state of light when the backlight device of FIG. 1 is used as a reflector.

FIG. 5 is a cross-sectional view showing a state in which a conventional backlight device is arranged on a lower surface side of a liquid crystal display element.

FIG. 6 is a view showing the optical axis of each member in FIG. 5;

FIG. 7 is a diagram showing a traveling state of light when illuminating a liquid crystal display element with the backlight device of FIG. 5;

FIG. 8 is a diagram showing a traveling state of light when the backlight device of FIG. 5 is used as a reflector.

DESCRIPTION OF SYMBOLS 1 Liquid crystal display element 3 Liquid crystal cell for display 4 Upper polarizer 5 Lower polarizer 14 Reflective polarizer 14a Reflection axis 14b Transmission axis 15 Light guide member 17 Reflector 18 Light source 20 Backlight device 21 Polarization conversion Liquid crystal cell

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09F 9/00 324 G09F 9/00 336J 336 G02F 1/1335 530 F-term (Reference) 2H049 BA02 BA07 BA42 BB06 BB63 BC22 2H089 HA22 HA24 QA16 RA05 RA09 2H091 FA08X FA08Z FA14Z FA23Z FA41Z FD05 FD08 HA07 HA12 LA17 LA18 5G435 BB12 BB15 EE27 FF03 FF05 FF08 GG24 KK05

Claims (5)

[Claims] 1. A backlight device provided on the back side of a display element, wherein the reflection axis is arranged to face the back side of the display element and reflects light of one polarization component and is orthogonal to the one polarization component. A reflective polarizing plate having a transmission axis through which light of the other polarization component is transmitted; a reflective plate disposed on a surface of the reflective polarizing plate opposite to the display element; the reflective polarizing plate and the reflective plate A light guide member disposed therebetween, and a light guide member disposed between the reflective polarizer and the reflective plate, and having a wavelength of (1 + 2n) / 4 (where n is a positive integer including 0) with respect to transmitted light. A polarization conversion liquid crystal cell that can be switched in response to a voltage application between a liquid crystal molecule alignment state in which a phase difference is generated to change a polarization state and a liquid crystal molecule alignment state in which no phase difference is generated with respect to transmitted light; Light source disposed on the end face side of the light member Backlight apparatus characterized by. 2. The backlight device according to claim 1, wherein the polarization conversion liquid crystal cell is a liquid crystal cell in which liquid crystal molecules are homogeneously aligned. 3. The backlight device according to claim 2, wherein the liquid crystal cell has a product Δnd · d of a refractive index anisotropy Δn and a cell gap d of 138 ± 20 nm. 4. The backlight device according to claim 1, wherein the polarization conversion liquid crystal cell is a liquid crystal cell in which liquid crystal molecules are twist-aligned. 5. The liquid crystal cell has a twist angle of 63.7 °.
Where the refractive index anisotropy Δn is 0.03 and the cell gap d is 6
The backlight device according to claim 4, wherein the thickness is 500 nm.