KR101064478B1 - Plane light emitting back light unit and lamp using point light source - Google Patents

Abstract

The present invention relates to a surface light emitting unit and a surface light emitting lamp that diffracts the light of a point light source such as a light emitting diode or a laser diode to be totally reflected inside the light guide plate and evenly distributes the light toward the front. The surface emitting backlight unit of the present invention includes a plurality of point light sources arranged at a predetermined interval behind the LCD panel to irradiate light toward the LCD panel, and light of a translucent material disposed between the LCD panel and the point light source. A diffraction means including a guide plate and having a back portion of the light guide plate to change the traveling direction of light irradiated from the point light source to a light irradiation area of each point light source so that the light guide plate is incident at an angle at which total internal reflection occurs; It is provided, and at least one side of the front portion and the rear portion of the light guide plate is characterized in that a plurality of light emitting means for changing the traveling direction of the light totally reflected inside the light guide plate to emit to the LCD panel side.

Point light source, LED, LD, light guide plate, diffraction grating, light emitting means

Description

Surface emitting backlight unit and surface emitting lamp using point light source {PLANE LIGHT EMITTING BACK LIGHT UNIT AND LAMP USING POINT LIGHT SOURCE}

The present invention relates to a surface light emitting unit and a surface light emitting lamp using a point light source, and more particularly, diffracted light of a point light source such as a light emitting diode or a laser diode to be totally reflected inside the light guide plate and evenly distributed to the front. A surface emitting backlight unit and a surface emitting lamp that emit light.

Recently, semiconductor light emitting devices such as LED (Light Emitting Diode) and LD (Laser Diode) have been widely used for backlight of indoor / outdoor lighting devices or display devices. The LED or LD has a high luminous efficiency compared to electric power, which can reduce power consumption and provide illumination of various colors, whereas the light emission angle is narrow due to the structural characteristics of the point light source. Therefore, in order to provide light of uniform brightness over a wide area, a separate means such as a light diffusion plate is required.

For example, a liquid crystal display (LCD) includes a backlight unit that provides light to the rear side because the liquid crystal panel itself does not emit light. As a light source of the backlight unit, a conventional cold cathode flourescent lamp (CCFL) is mainly used. In recent years, LEDs have been in the spotlight as devices capable of improving image quality and energy efficiency.

Currently used LED backlight units are largely divided into two types: edge emitting and direct illumination.

In the edge type, the LED is installed at the edge of the light guide plate to inject light into the light guide plate. When the incident light rays are diffused through the total internal reflection to the entire light guide plate, and meet the projection-shaped extraction point or the uneven scattering pattern, the light guide plate is vertically forward. It has a structure that is emitted to provide diffused light. Such an edge type structure not only makes it easy to uniformize the light intensity emitted from the light guide plate, but also has an advantage of making the thickness of the backlight unit thin.

However, as the size of the screen increases, the area of the screen increases in proportion to the square for each side length of the light guide plate on which the LED is installed. Therefore, the edge type backlight unit requires a high brightness LED because the required amount of light of each light source is increased. As the distance to reach is increased, not only the brightness of the LED but also the performance improvement of the light guide plate are required, which is disadvantageous in terms of manufacturing cost and process difficulty.

In contrast, the direct type provides uniform light by arranging the LEDs in two dimensions behind the liquid crystal and dispersing the light of each LED using a diffuser plate. It is possible to realize a large screen of the display device in the trend of large-sized, such as TV has a significant advantage over the edge type.

However, since point light sources such as LEDs have a non-uniform light distribution that is far from the center of light irradiation, i.e., a larger emission angle, the intensity of the light rapidly decreases, the direct backlight unit is close to the LED even when using a diffuser plate. The phenomenon that bright spots occur around a dot occurs, and diffusion plate improvement or other optical elements are required to remove the spot. In addition, in order to illuminate the required area due to the limited light irradiation angle, sufficient space must be secured between the liquid crystal and the LED, so that the thickness of the backlight unit and the liquid crystal display device must be increased.

In addition, the light distribution problem of the point light source generated when applied to the backlight unit as described above occurs even when the point light source is used in the lighting lamp.

The present invention is to solve the problems described above, by providing a point light source such as a light emitting diode or a laser diode in a direct type to realize a good image quality for a large display device, and at the same time a good light dispersion effect even at a point light source and a short distance It is an object of the present invention to provide a surface emitting backlight unit using a point light source capable of further improving image quality while reducing the thickness of a display device by providing an optical guide plate.

In addition, another object of the present invention is to provide a surface light emitting lamp using a point light source to uniformly diffuse and emit light of a point light source through a light guide plate to realize an even lighting effect over a wide area.

The present invention for achieving the above object, a plurality of point light sources arranged at a predetermined interval behind the LCD panel for irradiating light toward the LCD panel side, and a transparent material disposed between the LCD panel and the point light source And a light guide plate of the light guide plate, wherein the rear portion of the light guide plate is diffracted to change the traveling direction of the light irradiated from the point light source to the light irradiation area of each point light source so that the light guide plate is incident at an angle of total internal reflection Means are provided, and at least one side of the front portion and the rear portion of the light guide plate is characterized in that a plurality of light emitting means for changing the traveling direction of the light totally reflected inside the light guide plate to emit to the LCD panel side Provided is a surface emitting backlight unit using a point light source.

In the surface emitting backlight unit of the present invention, the diffraction means may be formed of a diffraction grating protruding at a predetermined period on the rear surface of the optical guide plate.

In addition, the diffraction means may be made of a diffraction optical element for forming a diffraction pattern on the back portion of the optical guide plate.

The light emitting means may be formed of a protrusion or a recess formed on the surface of the light guide plate.

In addition, the light emitting means may be made of a diffractive optical element or a hologram lens.

The point light source may be formed of a light emitting diode or a laser diode.

The period of the diffraction grating is preferably provided so that a second or more diffraction pattern is not formed in an angle range between 0 ° and 90 ° with respect to the vertical direction of the optical guide plate.

More preferably, the period of the diffraction grating is less than twice the value of the wavelength of light of the point light source divided by the refractive index of the optical guide plate.

The depth of the diffraction grating is preferably formed such that the luminous intensity of the first-order diffracted light is greater than that of the zero-order diffracted light.

In addition, the depth of the diffraction grating is more preferably odd times the value obtained by dividing the half-wavelength of the light of the point light source by a value obtained by subtracting 1 from the refractive index of the optical guide plate.

The diffraction grating has a rectangular cross-sectional shape, and the width ratio of the ridge and the valley is preferably 1: 0.1 to 1:10.

The diffraction grating may be provided in at least one of an array having a one-dimensional period, an array having a two-dimensional period, and an array having a circular symmetry.

The surface light emitting lamp using the point light source of the present invention includes a plurality of point light sources arranged at predetermined intervals to irradiate light forward, and an optical guide plate of a translucent material disposed in front of the point light source. The back portion of the plate is provided with diffraction means for changing the traveling direction of the light irradiated from the point light source to the light irradiation area of each point light source to be incident on the light guide plate at an angle at which total internal reflection occurs, and the front of the light guide plate At least one of the surface portion and the rear portion is characterized in that the light emitting means for emitting the front by changing the direction of travel of the light totally reflected inside the light guide plate.

In the surface light emitting lamp, the diffraction means may be formed of a diffraction grating protruding at a predetermined period on the rear surface of the optical guide plate, or may be formed of a diffraction optical element forming a diffraction pattern on the rear surface of the optical guide plate.

The period of the diffraction grating is provided so that a second or more diffraction pattern is not formed in an angle range between 0 ° and 90 ° with respect to the vertical direction of the optical guide plate, and the depth of the diffraction grating is 1 less than the intensity of the 0th diffraction light. It is preferable that it is formed so that the luminous intensity of the diffracted light becomes larger.

According to the present invention as described above, the direct light source arrangement and the edge-type light source arrangement by diffracting the light of the point light source is incident to be totally reflected inside the light guide plate and uniformly dispersed and discharged forward through a plurality of light extraction parts It is possible to provide a backlight unit for a large display device that realizes uniform brightness without using a high quality light guide plate and a high brightness point light source while simultaneously using the advantages of the method. Even if the distance between the light source and the diffraction grating is short, the effect of guiding light with the light guide plate is generated in the same way, thereby reducing the thickness of the display apparatus.

In addition, there is an effect that can provide a high-quality lighting lamp for irradiating light of uniform brightness over a wide area by uniformly diffused emission of the point light source through the light guide plate.

The objects, features and advantages of the present invention described above will become more apparent from the following detailed description. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 shows a first embodiment of a surface emitting backlight unit using a point light source according to the present invention.

The illustrated first embodiment illustrates an example in which an LED is provided as a point light source, and a plurality of LED point light sources 120 provided at a predetermined interval on the circuit board 110 and light provided in front of the point light source 120. It consists of a guide plate 130.

The point light source 120 is not installed at the outer end portion of the light guide plate like the edge type, but is arranged one-dimensionally or two-dimensionally at equal intervals behind the light guide plate 130 like the direct type.

The light guide plate 130 is preferably made of a synthetic resin material having high light transmittance, and is preferable in terms of moldability and cost. In particular, the optical guide plate 130 preferably has a refractive index of 1.3 or more in order to provide light diffraction and internal total reflection effects required by the present invention.

The rear portion of the light guide plate 130 is provided with a light transmissive diffraction grating 131 at an appropriate area according to the light irradiation range of the point light source 120 at each front of each point light source 120. The diffraction grating 131 changes the propagation angle of the light irradiated from the point light source 120 to be incident on the optical guide plate 130 at an angle at which total internal reflection occurs, and the propagation angle of the light is the diffraction grating ( 131).

Referring to FIG. 2, the refractive index of the optical guide plate 130 is n, the period of the diffraction grating 131 is d, the wavelength of light is λ, and the diffraction angle with respect to the vertical direction of the optical guide plate 130 is determined. When θ and a diffraction order are m, the diffraction angle of light by the diffraction grating 131 follows the following formula.

(수식 1)

(Equation 1)

The diffraction order m is an integer, and when m = 0, a 0th order diffraction pattern, and when m = 1, a first order diffraction pattern is shown. The diffraction angle θ of the diffraction pattern passing through the diffraction grating 131 increases as the period d decreases. When d is small enough (d <2λ / n), the diffraction patterns that can appear between -90 and 90 degrees are divided into three categories: 0th, -1st, and + 1st.

When the incident angle of light is 0 degrees, the diffraction angle θ of the zeroth order diffraction pattern is 0 degrees, and the diffraction pattern always occurs in a direction perpendicular to the plane on which the diffraction grating 131 is engraved. At this time, the energy distribution efficiency of each diffraction pattern depends on the depth h of the diffraction grating 131, and in the case of the zero-order diffraction pattern,

(수식 2)

(Equation 2)

In this case, destructive interference occurs and the diffraction efficiency decreases. Where k is an integer. In addition, when the diffraction grating 131 has a rectangular cross-sectional shape, when the width ratio of the floor and valleys of the diffraction grating 131 is 50:50, the energy ratio of the zero-order diffraction pattern is almost 0%. Accordingly, the diffraction grating 131 is preferably formed in a ratio of the width of the ridge and the valley of about 1: 0.1 to about 1:10.

Depending on the depth of the grating, the energy ratio of the zero-order diffraction pattern can be adjusted, thereby adjusting the amount of light passing in the vertical direction of the light source. As a result, when the energy of the 0th diffraction pattern decreases, the light emitted from the LED is converted to the +/- 1st diffraction pattern, and if the diffraction angle is sufficiently large, the guiding along the surface of the substrate is caused by total internal reflection. )do. This has a similar effect to placing the LED at the edge of the light guide plate in an edge type backlight unit to create a guiding mode. That is, each diffraction grating 131 changes the angle of the light of the point light source 120 to be incident into the light guide plate 130, and these lights propagate far away while being totally reflected inside the light guide plate 130. Therefore, the light irradiated from the plurality of point light sources 120 creates a uniform light distribution inside the light guide plate 130.

Furthermore, in the present invention, since the arrangement of the point light source 120 is uniformly distributed throughout the display device, such as a direct type LED backlight unit, the point light source 120 may have various advantages.

The front portion of the light guide plate 130 is provided with light emitting means 132 for emitting the light guided therein to the LCD panel in front of the light guide plate 130. The light emitting means 132 may be formed of protrusions or recesses formed on the surface of the light guide plate 130, or may be made of a diffractive optical element, similar to that provided in the light guide plate of the edge type backlight unit. In addition, the back of the light guide plate 130 may be provided with a light emitting means 133 consisting of a protrusion or recessed portion.

For example, when the refractive index of the optical guide plate 130 is 1.5 and the light wavelength of the point light source 120 is 465 nm, the total internal reflection angle is 41.8 degrees, and thus, when the first diffraction angle is 45 degrees, the first order Most of the diffraction patterns are guided by total internal reflection. When the period d of the diffraction grating 131 satisfying this is obtained from Equation 1, it is 438 nm. If the period is smaller than 438 nm, the diffraction angle is increased and the incident angle is larger than the total internal reflection angle, thereby satisfying the guiding conditions inside the optical guide plate 130. In addition, the depth of the diffraction grating 131 for minimizing the energy ratio of the zeroth order diffraction pattern may satisfy an odd multiple of 465 nm according to Equation 2 above.

The diffraction grating theory described above illustrates light traveling in the vertical direction of a one-dimensional grating for convenience of explanation and understanding. When applied, the diffraction grating makes a transmissive diffraction grating having a periodic structure in two directions. It can generate a guiding mode of light propagating in a direction perpendicular to the direction. In addition, the diffraction grating 131 may have various shapes as well as a rectangular grating shape. For example, when the diffraction grating 131 has a circular symmetry (concentric circle), the guiding mode having a circular symmetry is formed. Is generated.

As described above, the backlight unit of the present invention, like the direct type, the LED which is the point light source 120 is evenly distributed in the form of a two-dimensional array throughout the display device, and the light emitted from each point light source 120 is an optical guide plate ( Incidence perpendicular to the main plane of 130). At this time, the period and depth of the diffraction grating 131 is appropriately selected so that the diffraction pattern of the incident light is diffracted at a very large angle with respect to the vertical direction, and is reflected through the total internal reflection and far along the inside of the light guide plate 130. Let it spread. The light propagated as described above is mixed with the light of another point light source 120 incident through the other diffraction grating 131, and forms a uniform light distribution throughout the light guide plate 130. In addition, the light guided by the light emitting means 132, 133 through the light guide plate 130 is emitted to the front to form a surface light source for providing a light of uniform brightness to the LCD panel.

Therefore, the backlight unit of the present invention is equipped with the advantages of the direct type light source arrangement method and the edge type light source arrangement method at the same time without using a high quality light guide plate and high brightness LED, and also using a smaller number of LEDs, while providing uniform luminance. There is an advantage that can provide a backlight unit for a large display device that implements.

Moreover, in the case of the conventional direct type backlight unit, the distance between the LED and the diffuser plate should be sufficiently secured due to the limited area of light emitted from each LED, but the present invention provides a distance between the point light source 120 and the diffraction grating 131. Even if it is short, since the effect of guiding the light to the light guide plate 130 is the same, there is an advantage that can significantly reduce the thickness of the backlight unit.

On the other hand, in the above-described embodiment, the diffraction grating 131 is illustrated as a diffraction means for changing the traveling direction of the light irradiated from the point light source 120 and making it enter the optical guide plate 130 at an angle at which total internal reflection occurs. The diffraction means may be formed of a diffraction optical element that forms diffraction patterns of various shapes on the rear surface of the optical guide plate. The form of such diffractive optical elements is described in the literature (MT Gale, M. Rossi, H. Schutz, P. Ehbets, HP Herzig, and D. Prongue, Continuous-relief diffractive optical elements for two-dimensional array generation, Applied Optics, Vol. 32, Issue 14, pp. 2526-2533).

In addition, as in the second embodiment of the present invention illustrated in FIG. 3, a LD (laser diode) is provided instead of an LED as the point light source 120, and a diffractive optical element as the light emitting means 132. ) May be provided. The diffractive optical element may include a hologram lens. In this case, since the light having a uniform wavefront is incident on the diffraction grating 131 by using LD, the diffraction angle is defined more accurately, and the amount of light irradiated in the vertical direction by the diffraction optical element can be more precisely controlled. There is an advantage.

In the above-described embodiment, the present invention has been exemplarily described as being applied to the backlight unit of the display device. However, the present invention is not limited thereto, and the light of the point light source 120 may be formed by the light guide plate 130. It can be applied to a surface emitting lamp that diffuses through and provides an even intensity of illumination over a wide area.

The present invention described above is not limited to the above-described embodiment and the accompanying drawings, and various substitutions, modifications, and changes are possible within the scope without departing from the technical spirit of the present invention. It will be evident to those who have knowledge of.

1 shows a first embodiment of a surface emitting backlight unit using a point light source according to the present invention.

2 is an exemplary view for explaining the diffraction of light by the diffraction grating of the present invention.

3 shows a second embodiment of a surface emitting backlight unit using a point light source according to the present invention.

Description of the Related Art

10: 0 diffraction pattern 20: 1st diffraction pattern

110 substrate 120 point light source

130: light guide plate 131: diffraction grating

132, 133: light emitting means

Claims (18)

A plurality of point light sources arranged at a predetermined interval behind the LCD panel to radiate light toward the LCD panel, and an optical guide plate of a translucent material disposed between the LCD panel and the point light source, The rear portion of the light guide plate is provided with diffraction means for changing the traveling direction of the light irradiated from the point light source to the light irradiation area of each point light source to be incident on the light guide plate at an angle of total internal reflection, The diffraction means is a diffraction grating protruding at a predetermined period on the back portion of the optical guide plate, The period of the diffraction grating is such that the wavelength of light of the point light source is adjusted to the refractive index of the light guide plate so that a second or more diffraction pattern is not formed in an angle range between 0 ° and 90 ° with respect to the vertical direction of the light guide plate. Is less than twice the value divided by. The depth of the diffraction grating is an odd multiple of the value obtained by dividing the half wavelength of the light of the point light source by the value of the refractive index of the optical guide plate minus one so that the luminous intensity of the first diffracted light is larger than that of the zeroth order diffracted light. , At least one side of the front portion and the rear portion of the light guide plate is a surface using a point light source, characterized in that a plurality of light emitting means for changing the traveling direction of the light totally reflected inside the light guide plate to emit to the LCD panel side Light emitting backlight unit. delete The method of claim 1, And the diffraction means is a diffraction optical element for forming a diffraction pattern on the rear surface of the optical guide plate. The method according to any one of claims 1 to 3, The light emitting means is a surface light emitting unit using a point light source, characterized in that consisting of a protrusion or a recess formed on the surface of the light guide plate. The method according to any one of claims 1 to 3, And the light emitting means comprises a diffraction optical element or a hologram lens. The method according to any one of claims 1 to 3, The point light source is a light emitting diode or a laser diode surface-emitting backlight unit using a point light source, characterized in that. delete delete delete delete The method of claim 1, The diffraction grating has a rectangular cross-sectional shape, and the width ratio of the floor and the valley is 1: 0.1 to 1:10, the surface light emitting unit using a point light source. The method according to claim 1 or 11, wherein The diffraction grating is a surface emitting backlight unit using a point light source, characterized in that provided in the form of at least one of an array having a one-dimensional period, an array having a two-dimensional period, an array having a circular symmetry. A plurality of point light sources arranged at predetermined intervals to irradiate light toward the front, and a light guide plate of a translucent material disposed in front of the point light source, The rear portion of the light guide plate is provided with diffraction means for changing the traveling direction of the light irradiated from the point light source to the light irradiation area of each point light source to be incident on the light guide plate at an angle of total internal reflection, The diffraction means is a diffraction grating protruding at a predetermined period on the back portion of the optical guide plate, The period of the diffraction grating is the wavelength of light of the point light source to the refractive index of the optical guide plate so that a second or more diffraction pattern is not formed in an angle range between 0 ° and 90 ° with respect to the vertical direction of the optical guide plate. Is less than twice the division, The depth of the diffraction grating is an odd multiple of the value obtained by dividing the half wavelength of the light of the point light source by the value of the refractive index of the optical guide plate minus one, so that the intensity of the first-order diffracted light is greater than that of the zero-order diffracted light. At least one of the front portion and the rear portion of the light guide plate surface emitting lamp using a point light source, characterized in that the light emitting means for emitting the front by changing the traveling direction of the light totally reflected inside the light guide plate. delete The method of claim 13, The diffraction means is a surface light emitting lamp using a point light source, characterized in that the diffraction optical element for forming a diffraction pattern on the rear surface of the optical guide plate. delete delete The method of claim 13, The diffraction grating is a surface light emitting lamp using a point light source, characterized in that provided in the form of at least one of an array having a one-dimensional period, an array having a two-dimensional period, an array having a circular symmetry.

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