Patent Application
20100182799
1. Field of the Invention
The present invention relates to a planar light-emitting device, a panel, and a display device, and particularly relates to a planar light-emitting device, a panel, and a display device capable of realizing a thinner and lighter liquid crystal display device.
2. Description of the Related Art
In recent years, a liquid crystal display device is becoming popular. The liquid crystal display device displays images by controlling light transmittance incident on a liquid crystal panel thereof by each pixel. Therefore, a backlight for allowing light to be incident on the liquid crystal panel is incorporated in the liquid crystal panel in many cases (for example, see JP-A-Hei-11-174976 (Patent Document 1), JP-A-2004-12747 (Patent Document 2) and JP-A-2004-335405 (Patent Document 3)).
However, in the backlight of related art, it is sometimes difficult to reduce the thickness of a light guide plate used for the backlight. Thus, it is demanded to reduce the light guide plate for making the liquid crystal display device thinner in thickness and lighter in weight, however, it is difficult to sufficiently respond to the demand in the circumstances.
Thus, it is desirable to realize the thinner and lighter liquid crystal display device.
According to an embodiment of the invention, there is provided a planar light-emitting device including a light source and a light guide member propagating light from the light source, in which the light guide member is formed so that a light entrance portion on which light from the light source is incident is thicker than a body portion, and the light source includes a light-emitting member and a directivity member narrowing the directivity of light emitted from the light emitting member and allowing the light to be incident on the light entrance portion of the light guide member.
The directivity member of the light source may have a lens function.
The lens function may be a function of a convex lens or a prism lens.
The light source may include an LED (Light Emitting Diode), an LED semiconductor chip of the LED may be included as the light-emitting member and component members other than the LED semiconductor chip of the LED constitute the directivity member.
In the planar light-emitting device according to the embodiment of the invention, a light source and a light guide member propagating light from the light source may be provided. The light guide member may be formed so that a light entrance portion on which light from the light source is incident is thicker than a body portion. The directivity of light emitted from a light-emitting member by the light source may be narrowed through a directivity member, and the light may be incident on the light entrance portion of the light guide member.
According to another embodiment of the invention, there is provided a panel including a backlight having a light source and a light guide member propagating light from the light source, and a display unit displaying images by using light incident from the backlight, in which the light guide member is formed so that a light entrance portion on which light from the light source is incident is thicker than a body portion and the light source includes a light-emitting member and a directivity member narrowing the directivity of light emitted from the light emitting member and allowing the light to be incident on the light entrance portion of the light guide member.
In the panel according to the embodiment of the invention, a backlight having a light source and a light guide member propagating light from the light source, and a display unit displaying images by using light incident from the backlight may be included. The light guide member may be formed so that a light entrance portion on which light from the light source is incident is thicker than a body portion. The directivity of light emitted from a light-emitting member by the light source may be narrowed by a directivity member, and the light may be incident on the light entrance portion of the light guide member.
According to still another embodiment of the invention, there is provided a display device including a backlight including a light source and a light guide member propagating light from the light source, and a panel including a display unit displaying images by using light incident from the backlight, in which the light guide member is formed so that a light entrance portion on which light from the light source is incident is thicker than a body portion, and the light source includes a light-emitting member and a directivity member narrowing the directivity of light emitted from the light emitting member and allowing the light to be incident on the light entrance portion of the light guide member.
In the display device according to the embodiment of the invention, a backlight having a light source and a light guide member propagating light from the light source, and a panel including a display unit displaying images by using light incident from the backlight may be included. The light guide member may be formed so that a light entrance portion on which light from the light source may be incident is thicker than a body portion. The directivity of light emitted from a light-emitting member by the light source may be narrowed by a directivity member, and the light may be incident on the light entrance portion of the light guide member.
According to the embodiments of the invention, for example, when a liquid crystal display device is applied as the display device, it becomes possible to allow the liquid crystal display device to thinner in thickness and lighter in weight.
In order to make the understanding of the invention easier, a backlight in related art will be explained first. As a light source, a lamp and an LED (Light Emitting Diode) are chiefly used in many cases. Hereinafter, configuration examples of backlights of related art will be explained, which apply a lamp and an LED as light sources respectively.
A backlight shown in
In
The light guide plate 2 in the example of
On the lower surface 2b in surfaces orthogonal to the side surface 2a of the light guide plate 2 (lower surface 2b at a lower position of
The backlight shown in
The light guide plate 2 of the example of
On the lower surface 2b side of the light guide plate 2, the reflection sheet 11 is disposed. On the upper surface 2c side of the light guide plate 2, the diffusion film 12 is arranged for reducing luminance unevenness. Further, at an upper direction of the diffusion film 12 in
As described above, the shape of the light guide plate 2 has the wedge shape in examples of
It is not inevitably necessary that the light guide plate 2 has the wedge shape as described above. For example, even though the light guide plate 2 is a flat plate shape having a fixed thickness, the light guide plate 2 can exert a function of diffusing light from the light source on the surface of the backlight to uniform the luminance. However, when the shape of the light guide plate 2 is made to be the wedge shape, the light guide plate 2 can be made lighter in weight and can save material for the plate as compared with the light guide plate of the flat plate having the fixed thickness. Moreover, the front edge portion of the light guide plate 2 is thinner, therefore, it is possible to dispose a drive circuit of a display unit of the liquid crystal display device at the thin portion, which allows the entire liquid crystal display device to be thinner.
However, when considering the thickness of the light guide plate 2, it is difficult to allow the liquid crystal display device to be further thinner in thickness and lighter in weight by the simple wedge shape. It is because of the relation between the light guide plate 2 and the cold cathode tube 6 or the LED 14 as the light source. That is, when the size (thickness) of the side surface 2a of the light entrance portion (referred to as a light entrance surface 2a in the following description) of the light guide plate 2 is smaller than the size (thickness) of the cold cathode tube 6 or the LED 14 as the light source, the light entrance rate of light entering from the light source to the light guide plate 2 is reduced. Therefore, the size of the light entrance surface 2a of the light guide plate 2 is commonly set to the size which is equal to or larger than the size of the cold cathode tube 6 or the LED 14 as the light source.
As described above, it is difficult to reduce the size of the light entrance surface 2a to be the size less than the fixed size, therefore, when the simple wedge shape is applied as the shape of the light guide plate 2, it was difficult to allow the liquid crystal display device to be further thinner in thickness and lighter in weight.
Accordingly, the light guide plate 2 having the shape obtained by improving the wedge shape as shown in
In the light guide plate 2 in the example of
The light guide plate 2 of the example of
Accordingly, it is necessary to set the trumpet angle and the like of the light guide plate 2 in a range in which light entering into the light guide plate 2 does not escape out of the light guide plate 2 on the way. Accordingly, it is necessary to consider whether light entering into the light guide plate 2 escapes out of the light guide plate 2 on the way or not. In order to perform the consideration easily, in what manner light is guided into the light guide plate 2 will be explained as background art. Assume that a material of the light guide plate 2 is acrylic in the following description.
In
In the case of
In the case of
A refractive index “n” can be represented by the following equation (1) according to Snell's law.
n=sin β/sin α (1)
When the equation (1) is solved for the angle α, the angle α can be represented as the following equation (2).
α=a sin(sin β/n) (2)
In the equation (2), “a sin” represents an arcsine. This is the same in the following equations.
The refractive index “n” of light in the air region and in the light guide plate 2 is almost 1.49, therefore, the equation (2) can be represented as the following equation (3).
α=a sin(sin β/1.49) (3)
In
As shown by an arrow on the left side of
Hereinafter, the light guide plate 2 of the example of
In
When light incident angles are written in a manner that the first incident angle is “b”, the second incident angle is “c”, the third incident angle is “d” and so on, the relation of the incident angles “b”, “c” and “d”, the trumpet angle θ and the refracting angle α will be represented as the following equations (4).
b=90−α−θ
c=90−α−2θ
d=90−α−3θ
e=90−α−4θ
f=90−α−5θ (4)
When the right side of the equation (3) is substituted into the refractive angle α of the equations (4), incident angles b, c, d . . . can be calculated.
For example, when the trumpet angle θ of the light guide plate 2 is 3 deg, the right side of the equation (3) is substituted into the refractive angle α of the equations (4), the first light incident angle “b” can be represented by the following equation (5).
According to the equations (4), respective light incident angles b, c, d . . . the light guide plate 2 when the trumpet angle θ of the light guide plate 2 is changed to 2 deg, 3 deg, 6 deg, 8 deg . . . can be easily calculated. How light from the light source is guided inside the light guide plate 2 in the above cases is shown in
In
The incident angle “b” of the light with respect to the lower surface 2b is 46 deg according to the equations (4). In this case, the incident angle “b” is larger than 42 deg which is the critical angle, therefore, light is reflected on the lower surface 2b for the first time at a reflection angle b′=46 deg.
The light reflected on the lower surface 2b at the reflection angle b′=46 deg propagates inside the light guide plate 2 in the direction of the upper surface 2c.
The incident angle “c” of the light with respect to the upper surface 2c will be 44 deg according to the equations (4). In this case, the incident angle “c” is larger than 42 deg which is the critical angle, therefore, light is reflected on the upper surface 2 for the second time at a reflection angle c′=44 deg.
As described above, when the trumpet angle θ of the light guide plate 2 is 2 deg, the first light incident angle “b” and the second light incident angle “c” are both larger than 42 deg which is the critical angle, therefore, the light from the light source is guided inside the light guide plate 2.
In
The incident angle “b” of the light with respect to the lower surface 2b is 45 deg according to the equations (4). In this case, the incident angle “b” is larger than 42 deg which is the critical angle, therefore, light is reflected on the lower surface 2b for the first time at a reflection angle b′=45 deg.
The light reflected on the lower surface 2b at the reflection angle b′=45 deg propagates inside the light guide plate 2 in the direction of the upper surface 2c.
The incident angle “c” of the light with respect to the upper surface 2c will be 42 deg according to the equations (4). In this case, the incident angle “c” is just the same as deg which is the critical angle. Therefore, light is reflected on the upper surface 2c for the second time at a reflection angle c′=42 deg.
As described above, when the trumpet angle θ of the light guide plate 2 is 3 deg, the first light incident angle “b” and the second light incident angle “c” are both equal to or larger than 42 deg which is the critical angle, therefore, the light from the light source is guided inside the light guide plate 2.
In
The incident angle “b” of the light with respect to the upper surface 2b will be 42 deg according to the equations (4). In this case, the incident angle “b” is just the same as deg which is the critical angle. Therefore, light is reflected on the upper surface 2b for the first time at a reflection angle b′=42 deg.
The light reflected on the lower surface 2b at the reflection angle b′=42 deg propagates inside the light guide plate 2 in the direction of the upper surface 2c.
The incident angle “c” of the light with respect to the upper surface 2c will be 36 deg according to the equations (4). In this case, the incident angle “c” is less than 42 deg which is the critical angle, therefore, light incident on the upper surface 2c escapes out of the light guide plate 2.
In
The incident angle “b” of the light with respect to the upper surface 2c will be 40 deg according to the equations (4). In this case, the incident angle “b” is less than 42 deg which is the critical angle, therefore, light incident on the upper surface 2b escapes out of the light guide plate 2.
As described above, light entering into the light guide plate 2 from the light source propagates in a direction toward one of the lower surface 2b and the upper surface 2c of the light guide plate 2. When the incident angle to one of surfaces is equal to or larger than 42 deg, light is reflected on one surface and propagates in a direction toward the other surface, which will be repeated. However, as long as the lower surface 2b is inclined at the trumpet angle θ, the incident angle becomes smaller in proportion as reflection is repeated. As a result, light is not reflected at a position on the lower surface 2b or the upper surface 2c where the incident angle is smaller than 42 deg which is the critical angle, and escapes out of the light guide plate 2.
On the other hand, the first incident angle “b” with respect to the lower surface 2b is reduced in proportion as the trumpet angle θ becomes larger. Naturally, the incident angles after the second time will be further reduced. Therefore, the number of times that light entering into the light guide plate 2 from the light source repeats the reflection in the light guide plate 2 without escaping out of the light guide plate 2 (referred to as the number of repeated reflections in the following description) is reduced as the trumpet angle θ becomes larger.
For example, in the above example in which the light incident angle with respect to the light guide plate 2 from the light source is 90 deg and the lower surface 2b is inclined at the trumpet angle θ, the number of repeated reflections is two or more when the trumpet angle θ is equal to or smaller than 3 deg. However, when the trumpet angle θ is larger than 3 deg as well as equal or smaller than 6 deg, the number of repeated reflections is just once, that is, light is reflected only once. Moreover, when the trumpet angle θ is larger than 6 deg, for example, when the trumpet angle θ is 8 deg as shown in
That is to say, when the trumpet angle θ is set to be large, it is possible to make the entire display device thinner and lighter easily, whereas the number of repeated reflections is reduced. However, the length from the light entrance portion to the front edge portion is determined by a screen size of the display device. On the other hand, when light escapes out of the light guide plate 2, the light guiding efficiency of the light guide plate 2 is reduced, therefore, it is necessary to prevent light from escaping out of the light guide plate 2 wherever possible. Therefore, a certain number of repeated reflections has to be secured. This means that it is not always advantageous to simply set the trumpet angle θ to be larger.
However, the number of repeated reflections is confined because there is the condition that the lower surface 2b is inclined at the trumpet angle θ. When the upper surface 2a is parallel to the lower surface 2b, the number of repeated reflections is not confined. When 0=0 is substituted into the equations (4), incident angles “b” to “f” are all fixed to “90−α”, and light is reflected if “90−α” is equal to or larger than 42 deg. This will be explained with reference to
Here, a portion at which the lower surface 2b is inclined at the trumpet angle θ in the vicinity of the light entrance portion of the light guide plate 2 is referred to as a trumpet portion in the following description. The length of the trumpet portion is represented as “L”.
In
In
In
The incident angle “b” of the light with respect to the lower surface 2b is 45 deg according to the equations (4). In this case, the incident angle “b” is larger than 42 deg which is the critical angle, therefore, light is reflected on the lower surface 2b for the first time at a reflection angle b′=45 deg.
The light reflected on the lower surface 2b at the reflection angle b′=45 deg propagates inside the light guide plate 2 in the direction of the upper surface 2c.
The incident angle “c” of the light with respect to the upper surface 2c will be 42 deg according to the equations (4). In this case, the incident angle “c” is just the same as deg which is the critical angle. Therefore, light is reflected on the upper surface 2c for the second time at a reflection angle c′=42 deg.
The light reflected on the lower surface 2c at the reflection angle c′=42 deg propagates inside the light guide plate 2 in the direction of the upper surface 2b.
The incident angle “d” of the light with respect to the upper surface 2b will be 42 deg according to the equations (4) into which the trumpet angle β=0 is substituted. In this case, the incident angle “d” is just the same as 42 deg which is the critical angle. Therefore, light is reflected on the lower surface 2b for the third time at a reflection angle d′=42 deg.
After that, the light is guided inside the light guide plate 2 to the front edge portion while repeating reflections on the upper surface 2c or the lower surface 2b at the incident angle=the reflection angle=42 deg according to the equations (4) into which the trumpet angle β=0.
On the other hand, in
In
The incident angle “b” of the light with respect to the lower surface 2b is 45 deg according to the equations (4). In this case, the incident angle “b” is larger than 42 deg which is the critical angle, therefore, light is reflected on the lower surface 2b for the first time at a reflection angle b′=45 deg.
The light reflected on the lower surface 2b at the reflection angle b′=45 deg propagates inside the light guide plate 2 in the direction of the upper surface 2c.
The incident angle “c” of the light with respect to the upper surface 2c will be 42 deg according to the equations (4). In this case, the incident angle “c” is just the same as deg which is the critical angle. Therefore, light is reflected on the upper surface 2c for the second time at a reflection angle c′=42 deg.
The light reflected on the lower surface 2c at the reflection angle c′=42 deg propagates inside the light guide plate 2 in the direction of the upper surface 2b.
The incident angle “d” of the light with respect to the upper surface 2c will be 39 deg according to the equations (4). In this case, the incident angle “b” is less than 42 deg which is the critical angle, therefore, light incident on the upper surface 2b escapes out of the light guide plate 2.
As can be seen from
The number of repeated reflections inside the trumpet portion is determined by the trumpet angle θ and the first light incident angle on the upper surface 2c or the lower surface 2b. The latter condition, namely, the first light incident angle on the upper surface 2c or the lower surface 2b is determined by the refracting angle α of light which is incident on the light guide plate 2 from the light source, namely, the incident angle β at which light from the light source is incident on the light guide plate 2.
Accordingly, how light is guided inside the light guide plate 2 according to the difference of the incident angle β will be explained with reference to
In
The incident angle “b” of the light with respect to the lower surface 2b is 48 deg according to the equations (4). In this case, the incident angle “b” is larger than 42 deg which is the critical angle, therefore, light is reflected on the lower surface 2b for the first time at a reflection angle b′=48 deg.
The light reflected on the lower surface 2b with the reflection angle b′=48 deg propagates inside the light guide plate 2 in the direction of the upper surface 2c.
The incident angle “c” of the light with respect to the upper surface 2c will be 45 deg according to the equations (4). In this case, the incident angle “c” is larger than 42 deg which is the critical angle. Therefore, light is reflected on the upper surface 2c for the second time at a reflection angle c′=45 deg.
On the other hand, in the example of
The incident angle β=0 deg means that light from the light source enters to the upper surface 2c of the light guide plate 2 from the horizontal direction. That is, when the light from the light source is incident on the light guide plate 2 at the incident angle β=0 deg, the light propagates in parallel to the upper surface 2c and reaches the lower surface 2b.
At this time, the incident angle “b” of the light with respect to the lower surface 2b is 84 deg according to the equations (4). In this case, the incident angle “b” is larger than 42 deg which is the critical angle, therefore, light is reflected on the lower surface 2b for the first time at a reflection angle b′=84 deg.
The light reflected on the lower surface 2b with the reflection angle b′=84 deg propagates inside the light guide plate 2 in the direction of the upper surface 2c.
The incident angle “c” of the light with respect to the upper surface 2c will be 78 deg according to the equations (4). In this case, the incident angle “c” is larger than 42 deg which is the critical angle. Therefore, light is reflected on the upper surface 2c for the second time at a reflection angle c′=78 deg.
On the other hand, in the example of
As described above, the smaller the light incident angle β from the light source to the light guide plate 2 becomes, the larger the incident angle of light on the upper surface 2c or the lower surface 2b inside the light guide plate 2 becomes. Therefore, it can be seen that the trumpet angle θ can be taken larger when the incident angle β from the light source to the light guide plate 2 is made smaller. In the case that the trumpet angle θ is the same, the length “L” of the trumpet portion can be made longer in proportion as the light incident angle β from the light source to the light guide plate 2 becomes smaller.
The contents of the above description will be sorted out with reference to graphs of
In
The incident angles “b” to “g” show respective incident angles on the first to the sixth time with respect to the upper surface 2c and the lower surface 2b inside the light guide plate 2. Accordingly, the incident angles “b” to “g” are referred to as first to sixth light incident angles. The first light incident angle “b” is shown by a solid line (heavy line) curve. The second light incident angle “c” is shown by a dotted line (heavy line) curve. The third light incident angle “d” is shown by a dashed line curve. The fourth light incident angle “e” is shown by a double-dashed line curve. The fifth light incident angle “f” is shown by a solid (thin line) curve. The sixth light incident angle “g” is shown by a dotted line (thin line) curve. The contents of the paragraph are applicable not only to
For example, when the trumpet angle θ is 3 deg and the light incident angle β is 10 deg, the first light incident angle “b” is approximately 80 deg, the second light incident angle “c” is approximately 77 deg and the third light incident angle “d” is approximately 75 deg as shown in
On the other hand, for example, in the case that incident angle β of light from the light source is 70 deg, the first light incident angle “b” is approximately 48 deg, the second light incident angle “c” is approximately 45 deg and the third light incident angle “d” is approximately 41 deg even when the trumpet angle θ is the same at, for example, 3 deg. The fourth light incident angle “e” is approximately 39 deg, the fifth light incident angle “f” is approximately 36 deg and the sixth light incident angle “g” is approximately 32 deg. As just described, the first light incident angle “b” and the second light incident angle “c” are larger than 42 deg which is the critical angle. Therefore, the light entering from the light source is reflected on the lower surface 2b for the first time and is reflected on the upper surface 2c for the second time. However, the third light incident angle “c” is smaller than 42 deg, therefore, light is not reflected on the lower surface 2b for the third time, as a result, the light escapes out of the light guide plate 2.
As described above, when the trumpet angle θ is the same, the number of repeated reflections in the trumpet portion can be increased by reducing the light incident angle β from the light source, as a result, the length “L” of the trumpet portion can be made longer.
For example, when the light incident angle β from the light source is 10 deg and the trumpet angle θ of 9 deg, the first light incident angle “b” is approximately 75 deg, the second light incident angle “c” is approximately 67 deg and the third light incident angle “d” is approximately 58 deg as shown in
Moreover, for example, when the light incident angle β from the light source is 70 deg and the trumpet angle θ is 9 deg, the first light incident angle “b” is approximately 41 deg, the second light incident angle “c” is approximately 32 deg and the third light incident angle “d” is approximately 23 deg as shown in
As described above, when the trumpet angle θ is large, the number of repeated reflections in the trumpet portion is reduced even when the light incident angle β from the light source is the same, as a result, the length “L” of the trumpet portion is reduced. This will be further explained with reference to
In
For example, when the light incident angle β from the light source is 0 deg and the trumpet angle θ is 3 deg, the first light incident angle “b” is approximately 87 deg, the second light incident angle “c” is approximately 84 deg and the third light incident angle “d” is approximately 81 deg as shown in
On the other hand, for example, when the trumpet angle θ is increased to 9 deg under the condition that the light incident angle β from the light source is the same as 0 deg, the first light incident angle “b” is approximately 81 deg, the second light incident angle “c” is approximately 72 deg and the third light incident angle “d” is approximately 62 deg as shown in
In
For example, when the light incident angle β from the light source is 40 deg and the trumpet angle θ is 3 deg, the first light incident angle “b” is approximately 61 deg, the second light incident angle “c” is approximately 59 deg and the third light incident angle “d” is approximately 57 deg as shown in
On the other hand, for example, when the trumpet angle θ is increased to 9 deg under the condition that the light incident angle from the light source is the same at 40 deg, the first light incident angle “b” is approximately 57 deg, the second light incident angle “c” is approximately 47 deg and the third light incident angle “d” is approximately 38 deg as shown in
As described above, when the trumpet angle θ is large, the number of repeated reflections in the trumpet portion is reduced even when the light incident angle β from the light source is the same, as a result, the length “L” of the trumpet portion is reduced.
A method of forming graphs of
That is, all graphs of
Specifically, the graph shown in
Similarly, the graph shown in
Moreover, the graph shown in
That is, when the light incident angle β from the light source to the light guide plate 2 is “0 (zero)” deg, the first light incident angle “b” can be represented as the following equation (6) based on the equations (3), (4).
Similarly, the second light incident angle “c” can be represented as the following equation (7).
c=90−α−2θ
C=90−2θ (7)
The curves representing the above equations (6), (7) respectively will be the solid line (heavy line) curve representing the first light incident angle “b” and the dotted line (heavy line) curve representing the second light incident angle “c” respectively in the graph of
The dashed line curve representing the third light incident angle “d” to the dotted line (thin line) curve representing the sixth light incident angle “g” in
When the light incident angle β from the light source to the light guide plate 2 is 40 deg, a will be 25.6 according to the equation (3). Therefore, the first light incident angle “b” can be represented as the following equation (8).
The curve representing the equation (8) will be the solid line (heavy line) curve representing the first light incident angle “b” in the graph of
The dotted line (heave line) curve representing the second light incident angle “c” to the dotted line (thin line) curve representing the sixth light incident angle “g” in
As has been explained above, it is effective to reduce the thickness of the front edge portion “D” of the light guide plate 2 in order to allow the liquid crystal display device to thinner and lighter. In order to reduce the thickness of the front edge portion “D” of the light guide plate 2, it is effective to set the trumpet angle θ to be larger and the length “L” of the trumpet portion to be longer.
However, when the trumpet angle θ is set to be large and the length “L” of the trumpet portion is set to be long blindly, light escapes out of the light guide plate 2 without reflection in the trumpet portion, which reduces the light guiding efficiency of the light guide plate 2.
Accordingly, it is necessary to set the trumpet angle θ and the length “L” of the trumpet portion so as to satisfy the condition that all light incident angles in the trumpet portion are equal to or larger than 42 deg which is the critical angle to prevent light guiding efficiency of the light guide plate 2 from being reduced.
In this case, it is possible to visually recognize whether light incident angles in the trumpet portion, namely, the first light incident angle “b” to the sixth light incident angle “g” are equal to or larger than 42 deg as the critical angle or not by using the graphs of
Specifically, for example, the number of curves existing on a straight line representing 42 deg as the critical angle or existing above the straight line indicates the number of times that the light is reflected on the upper surface 2c or the lower surface 2b inside the light guide plate 2, namely, the number of repeated reflections. As the number of repeated reflections is increased, the length “L” of the trumpet portion can be set longer in proportion to the number. Conversely, when the length “L” of the trumpet portion is previously set, the maximum number of repeated reflections can be determined. It is effective to set the trumpet angle θ and the light incident angles β from the light source so that the same number of curves as the maximum number exists on the straight line representing 42 deg as the critical angle or above the straight line.
As apparent from
However, as the light source in related art, alight source 31 in which directivity of light is wide such as the lamp 6 of
As shown in
Accordingly, the present inventors propose a light source 41 including a light-emitting member and a directivity member which narrows light directivity from the light-emitting member as shown in
As can be seen easily when comparing
3. Configuration Examples of the Backlight on which the Light Source Applying the Invention is Mounted
Hereinafter, specific examples of the light source 41 to which the invention is applied (referred to as the light source 41 of the embodiment of the invention in the following description) will be explained.
The light source 41 of the embodiment of the invention includes LEDs 14 as the light-emitting member and a lens sheet 21 as the directivity member. That is, the lens sheet 21 is arranged between the plural LEDs 14 and a light entrance surface 2a as shown in
The lens sheet 21 has a shape whereby the directivity of light entering from the LEDs 14 to the light guide plate 2 can be narrowed. Accordingly, the lens sheet 21 is arranged between the LEDs 14 and the light guide plate 2, thereby narrowing the light incident angles β entering from the LEDs 14 to the light guide plate 2 to smaller angles. In other words, in light entering from the light source 41 to the light guide plate 2, the proportion of light fluxes having incident angles β close to 0 deg (parallel light with respect to the light guide plate 2) is high and the proportion of light fluxes having incident angles β close to 90 deg is low. As a result, the light guiding efficiency rises.
In other words, it is sufficient that the lens sheet 21 has a shape whereby the directivity of light entering from the LEDs 14 to the light guide plate 2 can be narrowed, and the shape is not particularly limited. For example, the lens sheet 21 may have various shapes as shown in
The shapes of
In each of examples of
The shapes of
In each of examples of
The shapes of
Hereinafter, operations of the light source 41 of the embodiment of the invention including the lens sheet 21 and the LED 14 having the above various shapes will be explained with reference to
As shown in
In
In the example of
In
As shown in
Accordingly, light emitted from the light source 31 of related art and passing through the lens sheet 21 will be the light from the light source 41 of the embodiment of the invention. The lens sheet 21 has a function of narrowing the directivity of light and increasing the front brightness thereof. In other words, the lens sheet 21 has a function of emitting light by allowing incident light to be close to parallel light.
Therefore, the directivity of light from the light source 41 of the embodiment of the invention is narrowed as compared with the directivity of light from the light source 31 of related art. This is shown in the drawing by the fact that the tear-drop shape indicating the directivity of light from the light source 41 of the embodiment of the invention shown in
The front brightness L2 of the light source 41 of the embodiment of the invention is increased as compared with the front brightness L1 of the light source 31 of related art. This is shown in the drawing by the fact that the length of a vector (length of an arrow) indicating the front brightness L2 of the embodiment of the invention shown in
The present inventors embodied an example of the light source 41 of embodiment of the invention by arranging the lens sheet 21 whose section is a prism lens shape in front of the light source 31 of related art made of a white LED 14 which is available in the market. Then, the present inventors measured the front brightness L2 of the light source 41 of embodiment of the invention. As a result, it was confirmed that the front brightness L2 of the light source 41 of embodiment of the invention has been at least 1.3 times as the front brightness L1 of the light source 31 of related art, that is, the front brightness L1 obtained when the lens sheet 21 is not arranged in front of the white LED 14.
As described above, the light from the light source 41 of the embodiment of the invention is close to parallel light as compared with the light from the light source 31 of related art.
The operations of the light source 41 of embodiment of the invention can be summarized as follows. Specifically, the light source 31 (LED 14 in related art) of related art can be applied as the light-emitting member. The lens sheet 21 can be applied as the directivity member. In this case, when light emitted from the light-emitting member passes through the directivity member, the directivity of light is narrowed as well as the front brightness is increased. In other words, the light emitted from the light-emitting member is close to parallel light by being passed through the directivity member.
In the above examples, the LEDs 14 of related art (refer to
Specifically, it is possible to allow the sealant 51 of the LED 14 to have the lens function. Accordingly, the LED including the LED semiconductor chip 52 as the light emitting member and the sealant 51 having the lens function as the directivity member can be used for the light source 14 of the embodiment of the invention.
More accurately, one of the plural unit light sources included in the light source 41 of the embodiment of the invention is the LED 14 shown in
In
In the example of
The sealant 51 having the so-called semi-cylindrical shape can exert the function of a convex lens with respect to the x-axis direction. As a result, it becomes possible to narrow the directivity of light of the light source 41 in the x-axis direction.
Also in this case, the sealant 51 having the so-called semi-cylindrical shape can exert the function of the convex lens with respect to the x-axis direction as shown in
Moreover, the sealant 51 having the concave lens shape can exert the effect of the concave lens with respect to the y-axis direction. As a result, the directivity of light of the light source 41 in the y-axis direction can be increased. Light entering from the plural unit light sources included in the light source 41 into the light guide plate 2 is brightened particularly in the vicinity of the center of each unit light source, therefore, unevenness of light sometimes occur. Accordingly, the directivity of light of the light source 41 in the y-axis direction is increased to disperse light in the y-axis direction, thereby reducing the unevenness of light.
Various examples of the light source 41 of the embodiment of the invention have been explained as the above. A destination to which the light source 41 of the embodiment of the invention is applied, namely, the backlight is not limited to the above examples and various embodiments can be taken. Particularly, there exist various examples in the shape of the trumpet portion of the light guide plate 2 as shown in
In the light guide plate 2 shown in
In the light guide plate 2 shown in
In the light guide plate 2 shown in
In the light guide plate 2 shown in
The light source 41 of the embodiment of the invention which has been described above is applied to the backlight, thereby taking the difference of thicknesses between the body portion and the light entrance portion of the light guide plate 2. That is, it becomes possible to set the trumpet angle θ of the light guide plate 2 to be larger or setting the length “L” of the trumpet portion to be longer by applying the light source 41 of the embodiment of the invention. As a result, for example, the following first advantage and the second advantage can be obtained.
The first advantage is that the body portion of the light guide portion 2 can be further thinner, thereby allowing the backlight to be thinner as well as allowing the liquid crystal display device to be lighter in weight and thinner in thickness.
The second advantage is as follows. That is, the light entrance surface 2a of the light guide plate 2 can be made thick, therefore, the light emitting member having the large size, for example, the LED 14 can be applied so as to correspond to the thickness. For example, assume that the same LED semiconductor chip 52 is put into LED packages of 0.3 mm and 0.8 mm respectively to constitute the LEDs 14. In that case, luminance obtained when put into the LED package of 0.8 mm is larger than luminance obtained when put into the LED package of 0.3 mm by 40% to 50%. Accordingly, the light emitting portion having the large size, for example, the LED 14 is applied to thereby realize improvement of luminance and the reduction of luminance deterioration at the display unit of the liquid crystal display. Such is the second advantage.
As described above, the liquid crystal display device has been explained as the display device to which the light source 41 of the embodiment of the invention is applied. The light source 41 of the embodiment of the invention can be applied to not only the liquid crystal display device but also all display devices which display images using the backlight.
The display device using the light source 41 of the embodiment of the invention can be also applied to various electronic apparatuses. As electronic apparatuses, for example, a digital still camera, a digital video camera, a notebook personal computer, a portable phone, a television receiver and the like can be cited. The display device can be applied to displays of electronic apparatuses in various fields, which display video signals inputted to such electronic apparatuses or generated in such electronic apparatuses as images or video. Examples of electronic apparatuses to which the display device is applied will be shown below.
For example, the invention can be applied to a television receiver as an example of the electronic apparatus. The television receiver has a video display screen including a front panel, a filter glass and the like, and manufactured by using the display device according to the embodiment of the invention as the video display screen.
For example, the invention can be applied to a digital still camera as an example of the electronic apparatus. The digital still camera includes an imaging lens, a display unit, a control switch, a menu switch, a shutter and the like, and manufactured by using the display device according to the embodiment of the invention as the display unit.
For example, the invention can be applied to a notebook personal computer as an example of the electronic apparatus. The notebook personal computer includes a keyboard operated when inputting characters and the like in the main body thereof and a display unit displaying images in a main-body cover. The notebook computer is manufactured by using the display device according to the embodiment of the invention as the display unit.
For example, the invention can be applied to a portable terminal device as an example of the electronic apparatus. The portable terminal device has an upper casing and a lower casing. There are a state in which these two casings are open and a state in which these are closed as the state of the portable terminal device. The portable terminal device includes a connection portion (hinge portion in this case), a display, a sub-display, a picture light, a camera and the like, in addition to the above upper casing and the lower casing, which is manufactured by using the display device according to the embodiment of the invention as the display or the sub-display.
For example, the invention can be applied to a digital video camera as an example of the electronic apparatus. The digital video camera includes a body portion, a lens for imaging a subject on a side surface facing the front, a start/stop switch at the time of imaging, a monitor and the like, which is manufactured by using the display device according to the embodiment of the invention as the monitor.
The embodiment of the invention is not limited to the above embodiment and can be variously modified in a range not departing from the gist thereof.
The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2009-007222 filed in the Japan Patent Office on Jan. 16, 2009, the entire contents of which is hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| P2009-007222 | Jan 2009 | JP | national |
