JPS623226A - Lighting device - Google Patents

Abstract

PURPOSE:To obtain a bright display having no irregularity in lighting by setting the ratio of apparent intervals between respective adjacent beltlike reflecting surfaces which are viewed in a visual angle direction and the apparent width of the respective beltlike reflecting surfaces in proportion to the distance from a light source. CONSTITUTION:A surface 20B of a light guide 20 is set almost in parallel to light from a light source 1 or at such an angle that it is in the shade of a beltlike reflecting surface 20A, and the light strikes on the surface 20B when it is observed in a specific direction. When the light guide 20 is observed in the specific visual angle direction, stripes where surfaces 20A where the light strikes and surfaces 20B where the light does not strike are arranged alternately are seen; the brightness of the beltlike reflecting surfaces 20A is constant without reference to the distance from the light source 1 and the brightness when stripes of light and shade is averaged is a/p times as large as the brightness of the beltlike reflecting surfaces 20A. when (b) is decreased, the mean brightness increases, but when the thickness (t) of the light guide 20 is increased and (b) is increased, the mean brightness decreases and the thickness (t) becomes small, so the ratio of (a) and (b) is varied according to required specification. Consequently, a thick lighting device which has small irregularity due to the light guide is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an illumination device using a light guide used for illumination means of passive display devices, particularly for backlighting of liquid crystal display devices.

<Prior Art> Display devices can generally be broadly classified into active (light-emitting) devices and passive (non-light-emitting) devices.

An active device is a light emitting diode display.

Displays are performed by emitting light themselves, such as plasma displays and electroluminescent displays. On the other hand, passive devices, such as liquid crystal display devices (hereinafter abbreviated as LCD) or electrochromic display devices, do not emit light themselves, but instead use natural light or other illumination sources by controlling the transmittance or reflectance of light. It modulates the irradiated light from the screen to display a pattern.

Therefore, the passive type device has a problem in that the display becomes difficult to see unless an illumination means is provided when the surroundings are dark.

LCDs are characterized by low power consumption and are widely used in portable electronic devices such as calculators and wristwatches. However, since the display mode of most LCDs utilizes the optical anisotropy of liquid crystals, overlapping polarizing plates is an essential component, and these polarizing plates are required to control the illumination light. About 50 inches will be cut. In particular, in a liquid crystal display device using a color filter, since the amount of light is further reduced due to colorization, it is essential to provide an illumination means to the device for general indoor use. Portable electronic devices are highly constrained by power supplies, and therefore, it becomes a challenge to produce display devices that consume less power and provide a powerful and bright illumination device.

On the other hand, when using in a bright environment such as outdoors during the day, if you rely only on illumination from an internal light source, the power consumption of the light source will increase if you try to increase the brightness of the display device to match the surrounding brightness. If it becomes too large, the low power consumption characteristics of the LCD will be impaired. Therefore, one way to make use of the advantages of LCD being a passive display device and having low power consumption is to use ambient light when the surroundings are bright.
A conceivable configuration is a light guide that illuminates the CD from the back and uses an internal light source to illuminate the CD when the surroundings are dark.

A backlight conventionally used as the above-mentioned internal illumination means is shown in FIG. 1O. i.e. light source
An incandescent miniature light bulb or a fluorescent lamp is used as 7゜1, and a milky white glass or synthetic resin plate with a light scattering effect is placed between the light source and the display panel IO to make the brightness of the illumination surface uniform over the entire surface. A diffuser-transmitting plate 4 is provided. Further, as the reflecting plate 5, a specular reflecting plate or a light scattering acrylic plate is used. This reflecting plate is provided to improve the efficiency of light utilization by reflecting the light emitted from the light source and directed toward the back surface and guiding it toward the front surface. However, with this kind of backlight, only 2 bright
- In order to reduce unevenness in brightness, it is necessary to maintain a certain distance between the light source l and the diffuser-transmitting plate 4, which has the disadvantage of increasing the depth.

On the other hand, edgelite as shown in FIG. 11 has been used conventionally. In this ride guide 6, the light incident from the light source l through the 0 surface is diffusely reflected on the roughened surface B, and then is transmitted through the A surface to the display panel 10 disposed close to the A surface. irradiated. This method has the disadvantage that the brightness of the B-plane becomes darker as the distance from the light source increases.

Moreover, as shown in FIG. 12, a parabolic shape (
When a tubular light source is used, a parabolic cylindrical reflecting mirror 7 may be used. In this case, the light reflected by the reflecting mirror 7 becomes a nearly parallel beam, but as can be seen from FIG.
The disadvantage is that the density of the luminous flux decreases as it moves away from the center.

It also has the disadvantage of increased depth.

<Object of the Invention> In view of the above-mentioned circumstances, the present invention provides a new and useful illumination device that is capable of achieving a bright display with high light utilization efficiency and no illumination unevenness by making full use of technical means for the shape of the light guide. The purpose is to provide equipment.

<Structure of the Invention> The present invention has been made focusing on the following principles 1 to 3.

(1) When observing a display panel from a certain direction, in order for the display panel to be uniformly illuminated, it is sufficient that the brightness of the backlight is uniform in that direction. The degree of divergence does not necessarily have to be uniform.

(2) The brightness when directly observing a light source is constant and does not depend on the distance between the light source and the observer.

(3) When observing light from a light source by reflecting it on a plane mirror, the brightness of the mirror image of the light source is equal to the brightness of the light source x the reflectance of the plane mirror, and at the position of the mirror image of the light source.

Not dependent.
In other words, the lighting device of the present invention focuses on this principle, and is a lighting device having a tubular light source and a plurality of strip-shaped reflective surfaces, in which each of the strip-shaped reflective surfaces reflects light from the light source in a predetermined viewing angle direction. The ratio of the distance (p) between adjacent strip-shaped reflective surfaces for visual acuity and the apparent width (a) of each strip-shaped reflective surface when viewed from the viewing angle direction and set at such an angle. It is characterized in that a/p is set to be proportional to the distance CD from the light source. Here, the predetermined viewing angle direction is not necessarily the direction τ perpendicular to the display panel surface.
There is no need to set this, and when using a display panel that is viewing angle dependent such as a liquid crystal display panel, the optimum viewing angle direction may be designed as the predetermined viewing direction.

FIG. 1 is an explanatory diagram showing the principle of the present invention.

2OA is a reflective surface, which causes the mirror image of the light source l to become IA
position. Since the angular distribution of the light emitted from IA is limited by 20A, it reaches only the shaded area in FIG. When the width of 2OA is sufficiently smaller than the radius R of the light source,
If the distance between the light source l and the reflecting surface 20A is D, the angle θ formed by the shaded area in FIG. 1 is 2 s ln (R/D), so the angular distribution of the reflected light is as shown in FIG. Width 2
It becomes a rectangular shape of sin (R/D). The same figure (a
t is the same figure when D is large and θ is small (bl is the case where D is small and θ is large.

Assuming that the angular distribution of incident light is represented by I(θ) and the characteristic of the diffuser plate is represented by D(θ), the angular distribution of diffusely transmitted light T(θ) is as follows.

However, D(θ) represents the ratio of the luminous intensity of the diffused light in the θ direction to the luminous intensity of the incident light when parallel rays are incident perpendicularly on the diffuser plate.

If the degree of diffusion of the diffuser plate, that is, the half-value width of D(θ) is smaller than the width of the angular distribution of the incident light,
As shown in , the maximum brightness does not depend on the width of the angular distribution of the incident light, as long as both ends of the angular distribution of the incident light are rounded.

On the other hand, when a diffuser plate with a high degree of diffusivity is used, the maximum luminance changes depending on the total amount of incident light, as shown in FIG. 9 [al[bl].

The present invention can achieve
This is a correction that cancels out the brightness change due to the distance from the light source and makes the brightness constant when viewed from a predetermined viewing angle direction.

<Example> Fig. 1 is a basic configuration diagram showing the principle of the present invention described above, and Fig. 2
The figure is an explanatory diagram showing details of the principle, FIG.

FIG. 4 is a cross-sectional view showing an example of a band-shaped reflective surface of a light guide used in the invention, and FIGS. 5 and 6 are cross-sectional views showing embodiments of the present invention.

First, in FIGS. 1 and 2, light emitted from the tubular light source lh is reflected by the band-shaped reflective surface 20A of the light guide 20 in a predetermined viewing angle direction (upward in the figures). In this case, light source 1
Since the mirror image of is formed at the position IA, the entire band-shaped reflective surface 20A appears to be shining when observed from the shaded area in FIG. On the other hand, the surface indicated by the reference numeral 20B of the light guide 20 is set at an angle such that it is almost parallel to the light directed to the light source 1 or is in the shadow of the band-shaped reflective surface 2OA, and when observed from a predetermined direction, It doesn't shine. The light guide 20 provides the surface 20B.
This is to reduce the overall thickness. The X and Y coordinates of each light guide 20 are determined by the following algorithm. Now, let the position of the tubular light source l be the origin of the X and Y coordinates, and the viewing angle direction be the Y-axis direction. In FIG. 2, the coordinates of both ends of the i-th strip-shaped reflective surface 2OA of the light guide 2o are (xi, yi) and (vi, wi), respectively. The angle that each of the 2OA plane and the 20B plane makes with the horizontal plane is α
Let i and βi. Further, the widths in the horizontal direction of the 20A surface and the 20B surface are respectively a and b. Follow Zeyfl “1”
2"6°, :・.

Now, give the end far from the light source l as the starting point.
1゜□1, then a series of first-order equations allows us to calculate the point near the light source.
[,! 1.1 Coordinates can be found sequentially.
゛7 sopa β1=arc tan(yi/xi
), □, α1=(90
°−ai) / 2, +,
v+=xi-a"wi=yi-a tan ai
', nxi+1=vi-b
,:,,yi+1=wi-b tan ai
,,:' When the light guide 20 with the shape obtained in this way is observed from a predetermined viewing angle, the light guide 20 ′:''・□ko゛;
'1゛'': Striped pattern in which side A and non-shining 20B side are arranged alternately.
・4'l I can see it. The brightness of the band-shaped reflective surface 2OA is as described above.
゛,' are constant regardless of the distance from the light source I. In addition, the brightness when the bright and dark stripes are averaged is the brightness of the band-shaped reflective surface 2OA.
It becomes a/p times the degree of □°. When b is small, the average brightness
Although the brightness increases, the thickness t of the light guide 20 also increases.If b is increased, the average brightness decreases, but the thickness t becomes thinner, so it is only necessary to change the ratio of a and b according to the required specifications. .

The present invention is characterized in that a/p is changed according to the distance from the light source since a counterfeit diffusion plate with a high degree of diffusion is used. A milky white plastic plate with a certain thickness or more has a high degree of diffusion and can be regarded as an approximately perfect diffusion surface, so a/
p is determined as follows. The brightness of a perfectly diffusing surface is constant no matter what direction it is viewed from, and it does not depend on the angular distribution of incident light, but is determined only by the luminous flux, that is, the illuminance, incident on the surface per unit area. Therefore, in order to keep the brightness constant, conditions should be set so that the illuminance of the light incident on the diffuser plate is constant. As shown in FIG. 1, the light reflected by the reflecting surface 2OA illuminates a wedge-shaped region shaded in the figure. The apex angle θ of this wedge shape is defined by the radius of the light source l being R, and the angle between the light source l and the reflecting surface 2.
If the distance between A and D is 2 sin (R/D
). If the pitch p of the reflective surfaces is small compared to R and one reflective surface and the diffusing surface are separated by a certain amount or more, the wedge-shaped heads illuminated by adjacent reflective surfaces will overlap each other. The degree of overlap increases as the apex angle θ of the wedge shape increases. Focusing on one point on the diffuser plate, the larger θ is, the more light from a large number of reflecting surfaces reaches the point.

The illuminance on the diffuser plate is approximately proportional to θ, and θ is approximately inversely proportional to D, so if a/p is made proportional to D, the illuminance on the diffuser plate becomes approximately constant regardless of the location. An example of calculation in this case is shown in FIG.

Note that it is not necessary to consider that the distance between the reflective surface and the diffuser plate changes depending on the location for the reason described below. The larger the distance between the reflective surface and the diffuser, the smaller the illuminance of light from each reflective surface, but the number of reflective surfaces illuminating one point is 4"L-, iJOM'fi4' !n
``Anus 8°''616・:.

As mentioned above, we have explained the case where the diffusion plate can be regarded as a perfect diffusion surface, but even when using a diffusion plate with an intermediate degree of diffusion, by changing a/p so that it is proportional to D, It was found that good results were obtained. For example, a/p=0.6 at the end far from the light source. FIG. 4I shows the result when a/p=0.3 at the end near the light source and linear interpolation in the middle. Incidentally, p does not need to be constant over the entire surface, and there is no problem as long as a/p is set to a predetermined value that satisfies the above-mentioned conditions. In Figs. 3 and 4, the pitch is increased to make it easier to move the force component.

There are two embodiments of the present invention, one shown in FIG. 5 and the other shown in FIG. That is, in the embodiment shown in FIG. 5, the light guide 20 is molded from transparent plastic, and the reflection inside the transparent plastic is used. If the incident angle to the reflective surface 2OA is larger than the critical angle h, total reflection will occur, but if it is less than the critical angle, some of the light will pass through, so a reflective layer made of metal or the like will be provided. The light from the light source is totally reflected on the upper surface of the light guide 20, producing a mirror image at the position IB, so that the usable light is doubled compared to the case shown in FIG. 6, which will be described in the next section.

Further, in the case of the embodiment shown in FIG. 6, since reflection from the outer surface of the molded body is used, there is no particular restriction on the material of the molded body. If the reflectance is low, a reflective layer will be provided thereon.

Effects> The present invention has the above-described configuration, and it is possible to obtain an illumination device with less uneven illumination and a thin thickness due to the thin light guide having uniform brightness.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing the principle of the present invention, Fig. 2 is an explanatory diagram of the principle, Figs. 3 to 4 are cross-sectional views showing an example of a band-shaped reflective surface of a light guide used in the present invention, and Fig. 5. and FIG. 6 are sectional views showing embodiments of the present invention, FIGS. 7 to 9 are explanatory views of the effects of the diffuser plate, and FIGS. 10 to 12 are sectional views of lighting devices showing conventional examples, respectively. It is. l... Tubular light source, 20... Light guide. 2OA...band-shaped reflective surface agent Patent attorney Aihiko Fukushi (and 2 others) Figure 1 - 1-, half α (←p-1 Figure 2 Figure 4 j ゛ . Figure 5 Figure 6 Figure 7. ,) Figure 8

Claims (1)

[Claims] 1. A lighting device having a tubular light source and a plurality of strip-shaped reflective surfaces arranged side by side for reflecting light from the light source, each of which reflects the light from the light source in a predetermined viewing angle direction. and the ratio of the apparent distance between adjacent strip-shaped reflective surfaces to the apparent width of each strip-shaped reflective surface when viewed from the viewing angle direction is set in proportion to the distance from the light source. A lighting device characterized by: