RU2431168C2 - Illumination device - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: backlighting device includes a plurality of light-emitting diodes (LED) having a light-emitting surface with light scattering angle in the angular aperture of up to ±90° from the normal to said light-emitting surface, a light guide plate made from transparent optical material and having a first surface which has light incidence zones. Each light incidence zone has a central area, a well as lateral areas in the immediate vicinity of the light incidence zones; a second surface having a plurality of concave areas interfaced with said zones and having a plane of symmetry. The lateral surfaces of the said concave areas have a shape which facilitates reflection owing to the effect of total internal reflection of part of the light coming from the light incidence zone within the angular aperture up to α=±arcsin (1/n) from the normal to the said light incidence zones, where n is the refraction index of the transparent substance. The device also has light output apparatus and a reflecting surface under the said light guide plate. The LEDs are placed under the light guide plate, and said central areas have a common plane of symmetry with interfaced concave areas and formed from two surfaces, the angle between which ranges from 120° to 60°.

EFFECT: improved design of the backlighting device.

3 cl, 6 dwg

Description

The invention relates to video technology, and more specifically to a backlight device for liquid crystal displays (LCDs). Such backlight devices are used to ensure uniform illumination of the LCD panel by radiation from the LED.

Known illumination devices with light sources spaced from one another in a plane behind the LCD panel, and equipped with a fiber guide plate with lateral transmission of a beam emanating from each LED. This configuration has an advantage over the design with the LEDs on one side of the LCD panel due to the improved temperature conditions, it also has a small thickness with high uniformity compared to designs based on LEDs with frontal radiation lenses. The light output device (it can be implemented as prism elements or diffusion devices installed on at least one surface of the light guide plate to change the direction of the light flux, mix light beams, etc.) provides uniform illumination of the LCD panel .

U.S. Patent Application Laid-Open No. 2007/0200118 [1] describes a backlight device comprising an array of light emitting diodes located between the reflective layer and the optical film provided with a plurality of optical elements disposed thereon, some of which, i.e. optical elements have funnel-shaped depressions with rotational symmetry to reflect the radiation of LEDs, and the shape of other optical elements does not have rotational symmetry. Under the optical elements is a reflective layer. In this case, the LED light cannot propagate upward through the region of the funnel-shaped recesses. The main disadvantages of this device are the lack of control over the uniformity of lighting and the angular aperture of the outgoing light, as well as the loss of light absorbed by the reflecting surface.

The backlight device described in US Pat. No. 6,679,621 [2] uses an additional film with reflective zones, but this design is too thick to provide uniform output lighting.

Closest to the claimed invention is a technical solution described in US Patent Application Laid-Open No. 2005/0264716 [3], which proposes a lighting structure for an LCD display (see FIG. 1), consisting of one LED or several LEDs spaced between by a given distance and placed in a row on the substrate, and from a molded element, the upper side of which is two curved surfaces of such a radius that provides complete reflection of the light flux emanating from the LED. In addition, a plurality of bulges on the upper side of the substrate form a light scattering means to provide uniform illumination at the output of the backlight unit. Such a design can provide fairly uniform illumination of the LCD panel, but it also has a number of disadvantages: the scattering or mirror substrate violates the TIR condition (TIR is the English abbreviation for the term "total internal reflection") on the lower surface of the molded part as a whole, therefore light losses occur to the substrate (1-10% of light loss during light reflection alone), in addition, there is no possibility of light propagating inside the molded part at a considerable distance from the light source, therefore The ability to mix luminous fluxes from various LEDs is very limited. The strictly defined geometry of the upper side (only two spherical surfaces) of the molded part does not allow the use of powerful LEDs to illuminate the LCD panel in this backlight design having a thin molded part.

The solutions known from the prior art can distinguish two main problems:

- very high requirements for tolerances in the manufacture of the profile of curvature of the lateral light emission elements;

- uncontrollable leakage of luminous flux on the lateral surfaces of the lateral light emission elements: the luminous flux from adjacent LEDs can easily pass through the lateral surfaces of the elements of neighboring cells.

The invention is aimed at solving these two problems.

The technical result is achieved due to the development of an improved design of the backlight device, while the inventive device includes:

- a plurality of LEDs having a light emitting surface with a scattering angle of the light flux in the angular aperture of up to ± 90 ° from the normal to said light emitting surface, wherein said LEDs are spaced from one another in a common plane,

- a light guide plate made of a transparent optical material, including:

- a first surface having light incidence zones, as well as central zones and side zones adjacent to the light incidence zones;

- a second surface having a plurality of concavities conjugated with said zones and having a plane of symmetry, the side surfaces of said concavities having a shape that allows reflection due to the effect of total internal reflection of a part of the light flux emanating from light incidence zones within the angular aperture up to α = ± arcsin (1 / n) from the normal to the mentioned light incidence zones, where n is the refractive index of the transparent substance;

- a means of releasing light, configured to provide a violation of the effect of total internal reflection;

- a reflective surface placed under said fiber guide plate;

wherein said central zones have a common plane of symmetry with conjugate concavities and are formed of two surfaces, the angle between which lies in the range from 120 degrees to 60 degrees.

A distinctive feature of the proposed solution is the geometric shape of the fiber plate. Thanks to this new shape, the fiber plate is thin and easy to manufacture. It is made with the possibility of integrating light fluxes and distributing them in a fiber guide due to the effect of total internal reflection (TIR effect) with virtually no loss.

The proposed geometry of the fiber plate and the design of the backlight device based on it provide a controlled uniformity of the light flux. The required degree of uniformity is ensured by optimizing the distribution of cells (here, a cell means a bunch of working elements for each LED) and optimizing the geometry of the side zone adjacent to the zone directly in contact with the light source on the lower surface of the fiber-optic plate.

The claimed geometry of the central zone located in the zone that is directly in contact with the light source provides acceptable manufacturing tolerances for the profile of the lateral light output means.

Further, the essence of the claimed invention is illustrated with the use of graphic materials.

Figure 1 - a known solution according to [3].

Figure 2 is one of the working options of the improved backlight device (see our patent application of the Russian Federation No. 2008109586 [4]).

Figure 3 - the backlight device according to the invention, which shows the following elements:

1 - plate-fiber,

2 - light source (LED),

3 - diffusely reflecting mirror,

4 - light-emitting surface of the light source,

5 - the first surface of the fiber plate,

6 - zone of incidence of light on the first surface,

7 - the Central zone in the zone of incidence of light,

8 - side zones on the first surface,

9 - the second surface of the fiber plate,

10 - concavity,

11 - lateral surface of concavity,

12 - plane of symmetry of concavity.

Figure 4 - the principle of operation of the Central zone in the zone of incidence of light.

Figure 5 - the principle of operation of the Central zone in the zone of incidence of light and the distribution of illumination in the Central zone.

6 is a principle of the side zone, which shows the following elements:

13 - rays passing through the lateral light emission means in known solutions (view 13.1),

14 - rays passing through the lateral light emission means and returning to the light guide plate in known solutions (view 13.1).

15 - rays reflected by the prismatic structure of the side zone according to the invention,

16 - rays transmitted through a prismatic structure of the side zone and reflected by the diffusion mirror according to the invention.

The claimed backlight device (Figure 3) consists of a plate-fiber 1, LEDs 2, placed under the plate-fiber at a distance from one another, a diffusion mirror 3, placed under the plate-fiber. LEDs 2 emit a luminous flux within an angular aperture of ± 90 ° and have a light-emitting surface 4 of a finite size. The said light guide plate 1 has a flat surface 5 with a plurality of light incidence zones 6, which are in optical contact with the light emitting surfaces 4 of the LEDs 2, while in each light incidence zone 6 there is a central zone 7, and, in addition, the first surface 5 has side zone 8, located in the immediate vicinity of the zone 6 of the incidence of light; and the second surface 9 with many concavities 10 with side surfaces 11. Each concavity 10 has a plane of symmetry 12 and forms a lateral light emission means that reflects the entire luminous flux coming from zones 6 within the angular aperture up to α = ± arcsin (1 / n) from the normal to said light incidence zones 6, where n denotes the refractive index of the transparent substance in accordance with the condition of total internal reflection. At least one of the surfaces of said light guide plate 1 has a lateral light emission means formed by concavities 10 and configured to violate the TIR condition in a certain area. The central zone 7 consists of concavity having a plane of symmetry coinciding with a plane of symmetry 12 from the corresponding means of lateral release of light.

The light emitting surfaces of the 4 LEDs are coupled to the light incident zones in such a way that the light rays do not experience refraction in the light incident zones (optical contact) except for the central zones 7 where light rays are refracted. In one embodiment, the size of the light emitting surfaces is the same as the light incidence zones. In another recommended embodiment, the size of the light emitting surfaces is smaller than the size of the zones of incidence of light rays.

In one embodiment, the central zone 7 is a prismatic concavity with two flat surfaces. This shape provides a deviation of the rays from the top of the lateral light emission means (Figs. 4 and 5). As a result, the rays from the light source 2 do not reach the top of the lateral light emission means and cannot reach the LCD panel directly, and therefore manufacturing tolerances in the manufacture of the vertex contour can be non-strict.

In one of the embodiments of the invention, the size of the Central zone 7 is made as coinciding with the size of the zone 6 of the incidence of light.

The lateral zones 8 are located in the immediate vicinity of the light incidence zones 6 in order to provide additional integration (mixing) of the optical signals and to prevent the partial derivative of the rays passing to the liquid crystal panel through the side surfaces 11 from the concavity 10.

In one of the embodiments of the claimed invention, the side zones 8 are implemented in the form of prism-like structures, thereby preventing the rays passing through the side surfaces of the lateral light emission means from entering the LCD panel. Figure 6 presents the principle of operation of the side zones. The view in FIG. 6.1 illustrates a known construction without a side zone: the rays 13 pass through the side surface of the light emitting lens to the LCD panel, the beam 14 passes outside the light guide plate, but it returns due to the specific form of the lateral light emission means. Such rays are not a problem in terms of uniformity of illumination. Fig.6.2 illustrates the case of the side zone 8, in which the rays 15, passing a path similar to the rays 13 from the view of Fig.6.1, are then reflected due to the total internal reflection and do not go beyond the plate of the fiber. Beam 16 is refracted by a prism-like structure and enters the diffusion mirror, therefore, some of the rays coming in the direction of the lateral light emission means are significantly weakened.

It is possible to use in the design of the inventive lighting device various optical sheet materials known from the prior art, such as: diffusion film, light-collimating film (e.g., BEF manufactured by 3M), polarization film (e.g., DBEF manufactured by 3M).

In the claimed solution, the prism forming the central zone 7 has an angle at the apex of 110 degrees, although in practice this angle can be assigned values in the range from 60 degrees to 120 degrees in order to achieve the required functionality. An angle of 120 degrees-100 degrees does not lead to an excessively large increase in the transverse concavity size 10.

In the claimed solution, the prism-like shape of the protrusions in the lateral zone 8 has the following geometric parameters: each prism-like formation has two flat surfaces, the first surface being perpendicular to the first surface of the fiber plate, the angle at the apex of the prism-like formation is 70 degrees, and the valid range of this angle lies ranging from 55 degrees to 80 degrees. This apex angle and prism-like shape should be optimized for a particular fiber guide plate with a specific kind of connecting elements.

The inventive backlight device can be used in LCD displays of televisions, in industrial displays and in other devices requiring backlighting.

Claims (3)

1. The backlight device, including
- a plurality of LEDs having a light-emitting surface with a scattering angle of the light flux in the angular aperture of up to ± 90 ° from the normal to said light-emitting surface, said LEDs being spaced from one another in a common plane,
- a light guide plate made of a transparent optical material, including:
a first surface having light incident zones that are in optical contact with the light emitting surfaces of the LEDs, and in each light incident zone there is a central zone as well as side zones located in close proximity to the light incident zones;
a second surface having a plurality of concavities conjugated with said zones and having a plane of symmetry, the side surfaces of said concavities having a shape that allows reflection due to the effect of total internal reflection of a part of the light flux emanating from light incidence zones within the angular aperture up to α = ± arcsin (1 / n) from the normal to the mentioned light incidence zones, where n is the refractive index of the transparent substance;
light emitting means configured to provide a violation of the effect of total internal reflection;
- a reflective surface placed under said fiber guide plate;
the LEDs are placed under the fiber guide plate, and the said central zones have a common plane of symmetry with conjugate concavities and are formed of two surfaces, the angle between which lies in the range from 120 to 60 °. 2. The device according to claim 1, characterized in that the said lateral zones are made in prism-like shape with an angle at the apex in the range from 55 to 80 °. 3. The device according to claim 1, characterized in that the central zones coincide in size of the base with the zones of incidence of light.

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