JP2001034210A - Plane display lamp and formation of light scattering body pattern - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plane display lamp having improved visibility of display characters, symbols, etc., by suppressing the luminance unevenness of the plane display lamp having a display area below about several 10 cm2 to <=3 times. SOLUTION: This plane display lamp consists of a planar light transmission body 12, a white bottom plate 16 covering the rear surface of the light transmission body 12, a white case frame 18 covering the flanks of the light transmission body 12, a diffusion sheet 20 covering the front surface of the light transmission body 12 and two LED devices 14a and 146 disposed by one piece each on the opposite flanks of the light transmission body 12. The rear surface of the light transmission body 12 is screen-printed with high reflection white ink, by which the dot patterns of a light scattering body are formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat display lamp, and more particularly to a light guide type flat display lamp having a light scattering function on the back surface of a light guide for uniformly extracting light to the outside. The present invention relates to a method for forming a light scatterer pattern that realizes a function.

[0002]

2. Description of the Related Art Various equipment and facilities used indoors include:
A flat display lamp (display area of about several tens of cm ² or less) for displaying the operation state, operation instruction, and the like is frequently used. As an example, there is a pilot lamp in which a light source such as a small incandescent lamp or a light emitting diode (LED) is attached to a case having a surface made of a colored plastic plate. When displaying characters or symbols on the surface of these display lamps, the brightness of the surface immediately above the light source is higher than that of the surroundings, and therefore, the brightness unevenness in the display surface is large, and the visibility of the displayed characters and symbols is poor. In addition, such a display lamp can basically only distinguish between two states by switching on and off. There are flat display lamps that have light sources with multiple emission colors installed under a translucent plastic plate, but the visibility is further deteriorated because the state of uneven brightness varies for each emission color compared to a single-color flat display lamp. I do.

As a means for reducing luminance unevenness, there is known a method used in a planar illumination device applied to a backlight for a liquid crystal display device. That is, a flat light guide is used as a flat light source, and a linear light source such as a fluorescent lamp or a point light source such as a plurality of LEDs is arranged around the flat light guide. In order for these light sources to emit light from the surface of the flat light guide with substantially uniform intensity, a method of providing a reflective layer having a distributed reflectance on the back surface of the light guide has been generally adopted.

[0004]

The above-mentioned conventional pilot lamp equipped with a light source such as a small incandescent lamp or an LED has a large luminance unevenness in the light emitting surface, so that the visibility of the displayed contents is poor and the display quality is low. There is a problem.

[0005] Further, a flat display lamp provided with a light source having a plurality of luminescent colors to switch between a plurality of luminescent colors cannot provide good display quality.

When a flat lighting device using a flat light guide is used for a flat display lamp, it is difficult to reduce the size of the flat lighting device by using a fluorescent lamp as a light source.
The use of the ED has a problem that electric wiring becomes complicated and power consumption increases.

An object of the present invention is to provide a flat display lamp which utilizes a flat light guide as a flat light source and solves the above-mentioned problems.

Another object of the present invention is to provide a display area of several tens c.
An object of the present invention is to provide a flat display lamp in which luminance unevenness is suppressed to three times or less in maximum / minimum brightness of a flat display lamp of about m ² or less, and visibility of displayed characters, symbols, and the like is improved.

It is still another object of the present invention to provide a flat display lamp which can easily drive a light source and consumes less power.

It is still another object of the present invention to provide a method for forming a light scatterer pattern to be printed on the back surface of a flat light guide.

[0011]

SUMMARY OF THE INVENTION A rectangular plate light guide 1 is provided.
An LED device, which is one point light source, is arranged at the center of each of the sides or two opposing sides. In order to reduce the uneven brightness of the light emitted from the front surface of the light guide, a light scatterer pattern in which the reflected light intensity is two-dimensionally distributed is formed on the back surface of the light guide.

Each one LED device is in the same package,
One with one LED chip mounted, or for example R
A device in which a plurality of LED chips such as three primary colors of GB are mounted close to each other can be used. When a plurality of LED chips are mounted close to each other, not only turning on / off the lighting but also switching the display color by electrical control becomes possible.
In this case, since the plurality of LED chips are arranged close to each other, the luminance unevenness does not substantially change during the emission of each color, and the plurality of states can be identified and displayed by the emission colors.

An important point of the present invention is that the point light source LE
The light emitted from the device D is taken into the flat light guide, and the light scatterer pattern is provided on the back side of the light guide light emitting surface so as to have uniform brightness within the light emitting surface of the light guide, that is, light emission luminance. Is formed. By adjusting the pattern shape so as to have a certain regularity, the entire light emitting surface of the light guide had a uniform luminance distribution, and a flat display with apparently uniform brightness became possible.

In the conventional light scatterer pattern, the pattern near the light source is basically sparse, and the pattern becomes denser as the distance from the light source increases. However, when a single point light source is used, this pattern is not necessarily required. Such patterns are not optimal and may require more complex patterns.

In order to realize such an optimum pattern,
The method of forming the dot pattern of the light scatterer on the back surface of the light guide is important.

The method of forming a dot pattern of a light scatterer according to an embodiment of the present invention includes the following steps: a) Light is uniformly distributed on the entire back surface of an evaluation light guide made of the same material as the light guide used for the flat display lamp. Forming a scatterer; b) assembling a flat indicator light; c) measuring a brightness distribution at each coordinate of a light emitting surface of the flat indicator light; d) using a minimum value of the brightness distribution as a reference. Converting the measured luminance of the coordinates into a standard value by performing an inverse proportional operation; e) calculating the area of the dot of the light scatterer at each coordinate from the standard value obtained by the conversion; and f) calculating the calculated value. Forming the dot pattern of the light scatterer on the back surface of the new light guide.

[0017]

FIG. 1 is an exploded perspective view of a flat display lamp according to an embodiment of the present invention.

The flat display lamp 10 has a size of 50 × 25 × 5 m.
The light guide 12 is made of a transparent acrylic resin in the form of a flat plate that has been cut to a size of m. This light guide is provided at the center of the side surface on the opposite short side, respectively, with the LED devices 14a and 14a.
14b is provided. The LED device is manufactured by Nichia Corporation and has a green dominant wavelength of 530 nm and a forward current of 20 mA.
A 1.5 mW output was used. The size of one LED light source (semiconductor chip) is 0.3 mm x 0.3 mm
The opening (light emitting portion) of the light extraction window of the LED package on which one chip is mounted has a size of about 1 × 2 mm.

The transparent acrylic light guide 12 has a white bottom plate 16 on the bottom surface and four white
8 covered. The diffusion sheet 20 is attached to the upper surface of the white case frame 18, that is, the light emitting surface side. Such white case 18 and white bottom plate 16 are made of white ABS.
Resin was used.

A light scatterer was formed on the back surface 13 of the light guide 12 by screen printing using a high-reflection white ink manufactured by Teikoku Ink Mfg. Co., Ltd. to draw a specific pattern. The pattern of the light scatterers is usually circular dots.
A specific procedure for designing a print pattern will be described in detail below.

First, the above-mentioned high-reflection white ink is solid-printed on the entire back surface of the light guide 12, and the light guide is placed in a white case 18 and covered with a white bottom plate 16. A diffusion sheet is attached to the surface side, and a flat indicator light for designing a light scattering body pattern is assembled. And each LED
Then, the luminance distribution in the light emitting surface when a direct current of 20 mA is applied is measured.

As described above, the LED devices 14a and 14b are provided on the opposite side surfaces 15a and 15b of the light guide 12.
When the light emitting surface is equally divided into four regions by orthogonal lines, the luminance distribution of each region is the same, so that the luminance distribution of one region may be measured. FIG. 2 shows a state where the light emitting surface is indicated by xy coordinates. The coordinates were set such that the X axis was divided into 25 equal parts and the Y axis was divided into 50 equal parts with one corner of the light emitting surface as the origin. A state where the light emitting surface is divided into four regions by lines 22 and 24 orthogonal to each other at the center of the light emitting surface is shown. The luminance distribution is measured for a quarter region 26 which is hatched.

Once the luminance distribution for one region 26 has been measured, the measured luminance distribution is
If the right and left lines are symmetrically applied to the orthogonal lines 22 and 24, the luminance distribution of the entire light emitting surface is obtained.

FIG. 3 shows the measured luminance distribution data of the area 26. As shown in FIG. FIG. 3 is a table showing the distribution of luminance (cd / m ² ) at each point (x, y) from the origin to coordinates 12 in the X-axis direction and coordinates 25 from the origin in the Y-axis direction. FIG.
It is a histogram which shows a brightness distribution in three dimensions. FIG. 4 shows that the luminance takes the lowest value at the coordinates (0, 0), and the luminance is high in the coordinate area close to the LED. Such luminance unevenness was 4.4 times the maximum / minimum ratio in the plane.

Next, a standardized distribution obtained by normalizing the minimum value of the luminance distribution shown in FIG. 3 as a reference and inversely transforming the measured luminance is created as shown in a table of FIG. The lowest value of the luminance distribution shown in FIG. 3 is 98.76 cd / m ² of the coordinates (0, 0), and the luminance of the other coordinates is normalized in inverse proportion based on this. That is,

[0026]

(Equation 4)

Is calculated (normalized). The obtained numerical value is inversely proportional to the luminance, and decreases as the luminance increases. Note that the standard values in FIG. 5 are values when A = 1.

Next, a method of allocating a circular dot pattern of the light scatterer to each coordinate will be described. The radius of the circular dot per unit area (mm ² ) based on the standard value of FIG.

[0029]

(Equation 5)

The table shown in FIG. 6 is calculated from the relational expression with A = 1. The numerical values indicate the diameter of the circular dot at each coordinate, and the printing pattern plate is manufactured by regarding the diameter of the printing dot pattern in a square segment of 1 mm ² .

Using the produced printing pattern, a circular dot pattern is printed on the back surface of the light guide. FIG. 7 shows an example of a printed circular dot pattern. Here, what is shown in black is a circular dot pattern, and the reflectance of this portion is high. The reflectance has a characteristic that it is minimized at two places in the plane.

Using the light guide 12 having the above-described circular dot pattern printed on the back surface, a flat display lamp was assembled. That is, the white bottom plate 16 was attached to the bottom of the light guide 12, the white case frame 18 was covered, and the diffusion sheet 20 was attached to the light receiving surface. In such a flat indicator light, L
The ED devices 14a and 14b were turned on, and the luminance distribution was measured. The measured values are shown in FIG. Maximum brightness at coordinates (22, 10) and 118.9cd / m ^2, a minimum luminance at coordinates (4, 12) is 60 cd / m ^2, the luminance unevenness, the maximum /
It was found that the minimum ratio was 1.98 times, which was almost doubled.

In order to obtain a more uniform luminance distribution, the luminance is once corrected by the pattern design method described above, and then the luminance distribution is measured by the same method to obtain a standard value distribution. It is also effective to perform normalization again and secondary correction. By repeating the correction up to the n-th order, uniform and high luminance can be obtained on the light emitting surface of the light guide.

In the above description, one L is provided on one LED device.
An example of a monochromatic light source on which an ED chip is mounted has been described. However, when a plurality of LED chips are mounted on one LED package, a light guide is used regardless of which of the chips emits light. Since the geometric positional relationship of the point light sources, which are light emitters, is substantially constant, the light emitted from the LED chip is similarly distributed from the light emitting surface of the light guide. That is, a light emitting surface having a uniform luminance distribution over the whole is obtained. For example, a red (R), green (G), and blue (B) LED chips mounted and arranged in the same LED package so that the distance between their center points is about 1 mm is used as a light source. . R, G, and B colors can be switched to light, and two or three colors can be lighted simultaneously to mix colors. If the distance between the point light sources is small as described above, even if the same dot pattern is used, a change in luminance unevenness due to each light emitting point can hardly be visually recognized. The plurality of chips may be of the same color. In this case, display can be performed by switching the luminance level.

In the above embodiment, the long side of the flat light guide plate is 5
Although it is 0 mm, it can be used in a range of about 20 to 200 mm. However, the luminance depends on the intensity of the emitted light from the LED, and if the light intensity is the same as in the above embodiment, the luminance of the display and the like decreases as the size increases. Further, it is necessary to redesign the dot pattern every time the size of the light guide plate is changed.

Further, in the above embodiment, the light scatterer is constituted by circular dots, but it is not limited to a circular dot. Rather, a square pattern having the same shape as the segment provides more consistency between the luminance and the area ratio (the minimum luminance portion is the entire segment printing surface, and the ratio to that is allocated to each segment). Further, many deformations such as a rhombus are possible.

FIG. 9 is a view showing another embodiment of the flat display lamp of the present invention. The indicator light 22 has a structure shown in FIG. 1 in which a light-shielding plate 26 made of metal or plastic, on which characters or symbols 24 are punched, is attached on the diffusion sheet 20. Conversely, opaque characters and symbols may be printed or pasted on a transparent glass or plastic plate.

As described above, a flat display lamp capable of displaying characters or symbols can be obtained.

In the above embodiment, the screen printing method was used as the method for forming the light scatterer. However, various organic and inorganic light diffusing materials (mainly white paint) were introduced by the offset printing method, the ink jet printing method or the like. It can also be applied to the back surface of the optical body to form a scattering pattern.

Instead of applying a high reflector as described above, there is a method of extracting light by roughening the back surface of the light guide. Roughening the surface by mechanical processing, for example, forming a large number of minute irregularities by sandblasting, or applying direct scattering treatment to the injection molding die and transferring it during molding, making linear grooves by SC processing, etc. It is also possible to adopt the method described above. Basically, it is the use of the light diffuse reflection effect by roughening the surface unevenness or the like.

Furthermore, a method in which a large number of small-area inclined surfaces are formed on the back surface of the light guide and light is emitted from the opposite surface, that is, a shape in which the light reflection angle at the emission surface is less than the critical reflection angle Can also be used.

[0042]

According to the present invention, since an LED which is a semiconductor element is used as a light source, a high-voltage circuit is not required in a drive circuit, and a long-life and highly reliable flat display lamp can be realized.

Further, since one or a small number of small-sized point-like LEDs are used, a small, light-weight, compact, and low power consumption flat display lamp can be obtained.

Further, since such a flat display lamp uses a light guide on which light scattering dots are formed by the pattern forming method of the present invention, a uniform luminance distribution can be obtained.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of one embodiment of a flat display lamp of the present invention.

FIG. 2 is a diagram illustrating a state in which a light emitting surface is represented by xy coordinates and divided into four regions.

FIG. 3 is a diagram showing a table of measured brightness distribution data of a flat display lamp when the back surface of a light guide is solid-printed with high reflection ink.

FIG. 4 is a histogram three-dimensionally showing the luminance distribution in FIG. 3;

FIG. 5 is a diagram showing a table of a standard distribution.

FIG. 6 is a diagram showing a table representing calculated radiuses of circular dots.

FIG. 7 is a diagram showing a part of a printed circular dot pattern.

FIG. 8 is a diagram showing a table of measured luminance distribution data of the flat display lamp when a circular dot pattern is printed on the back surface of the light guide.

FIG. 9 is an exploded perspective view of another embodiment of the flat display lamp of the present invention.

[Explanation of symbols]

 10, 22 Flat indicator lamp 12 Light guide 14a, 14b LED device 15a, 15b Side surface 16 White bottom plate 18 White case frame 20 Diffusion sheet 24 Stamped character 26 Shield plate

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C096 AA05 BA02 BC19 CA04 CA13 CA25 CA26 CA32 CB01 CC06 CD05 CD14 CD24 CD32 CE29 FA12 FA16 FA17 5G435 AA01 BB04 CC05 CC07 DD13 EE27 FF08 GG23 GG26 LL01

Claims (11)

[Claims] A planar light guide, a white bottom plate covering a back surface of the light guide, a white case frame covering a side surface of the light guide, a diffusion sheet covering an upper surface of the light guide, A flat display lamp comprising a point light source disposed on one side surface or two opposing side surfaces of a light guide, and a back surface of the light guide configured to scatter light. 2. The flat display lamp according to claim 1, wherein a light-shielding plate on which characters or symbols are punched is provided on the diffusion sheet. 3. The flat display lamp according to claim 1, wherein a light transmitting plate on which characters or symbols are drawn is provided on the diffusion sheet. 4. The device according to claim 1, wherein the point light source is an LED device on which one LED chip is mounted.
The flat indicator light according to 2 or 3. 5. The flat display lamp according to claim 1, wherein a plurality of LED chips are mounted close to each other on said LED device. 6. A planar light guide, a white bottom plate covering a back surface of the light guide, a white case frame covering a side surface of the light guide, a diffusion sheet covering an upper surface of the light guide, A method of forming a dot pattern of a light-scattering body on the back surface of a light guide of a flat display lamp comprising a point light source disposed on one side surface or two opposite side surfaces of the light guide, respectively: A step of uniformly applying a light scatterer on the entire back surface of the evaluation light guide made of the same material as the light body; b) assembling the flat indicator light; c) a light emitting surface of the flat indicator light Measuring the luminance distribution at each coordinate of d), d) converting the measured luminance of each coordinate to the standard value by performing an inversely proportional operation on the basis of the lowest value of the luminance distribution, and e) converting the standard obtained by the conversion to a standard value. Calculate the dot area of the light scatterer at each coordinate from the value And f) forming the calculated dot pattern of the light scatterer on the back surface of a different light guide from the light guide for evaluation. Forming method. 7. g) assembling the flat display lamp using the light guide produced in the step f); h) measuring a luminance distribution at each coordinate of a light emitting surface of the flat display lamp; i) a step of inversely proportionally calculating the measured luminance of each coordinate on the basis of the lowest value of the luminance distribution to convert the measured luminance into a standard value; j) the area of the dot of the light scatterer at each coordinate from the standard value obtained by the conversion. When calculating the above, reflecting the change from the standard value obtained in the step d; and k) changing the calculated dot pattern of the light scatterer to another light guide in the step f. Forming a light guide on the back surface of another light guide, and l) repeating the steps g to k n times (n is an integer of 0 or more) with respect to the light guide created in the step k; 7. The method according to claim 6, wherein Method of forming the mounting of the light scatterer pattern. 8. In the steps d and i, the conversion into the standard value is performed by the following equation: 8. The method for forming a light scatterer pattern according to claim 6, wherein: 9. The dot shape of the light scatterer is given by: The method for forming a light scatterer pattern according to claim 8, wherein the shape satisfies the following. 10. When the light scatterer is a circular dot, the radius of the light scatterer is determined by the following equation in the steps e and j. The method for forming a light scatterer pattern according to claim 8, wherein the calculation is performed by: 11. The light according to claim 6, wherein the dot pattern of the light scatterer is formed so as to have a minimum reflectance near the point light source. A method for forming a scatterer pattern.