WO2010049857A1

WO2010049857A1 - Light guide plate and illumination device using the light guide plate

Info

Publication number: WO2010049857A1
Application number: PCT/IB2009/054667
Authority: WO
Inventors: Yadong Liu; Gongming Wei; Bo Liu; Jun Ren; Hugo Johan Cornelissen
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2008-10-31
Filing date: 2009-10-22
Publication date: 2010-05-06
Also published as: TW201020472A

Abstract

The invention discloses a light guide plate comprising: a first surface; and a second surface; wherein the first and the second surface are substantially parallel to each other, and at least one of the first and the second surface has a surface structure which comprises a plurality of deflection means (21), each deflection means having an abrupt slope (17) and a gentle slope (18); the directrixes of the peaks of the deflection means and the valleys between different deflection means being substantially smooth curves. The invention further discloses an illumination device used to illuminate a surface, comprising: a lighting element, an illuminating body, and a housing element; wherein the illuminating body comprises said light guide plate, and said deflection means are configured to receive and deflect the light emitted from the lighting element onto the surface to be illuminated. Because of the smooth structure of the peaks and connection parts of the deflection means in the surface structure, the illuminating body of the illumination device, i.e. the light guide plate, has characteristic anti-scratch and anti-abrasion features.

Description

LIGHT GUIDE PLATE AND ILLUMINATION DEVICE USING THE

LIGHT GUIDE PLATE

FIELD OF THE INVENTION

The present invention relates to an illumination device, particularly a light guide plate used as an illuminating body.

BACKGROUND OF THE INVENTION

International patent application WO2008/087593 discloses an illumination device normally configured to illuminate a surface, which device includes a lighting element, a housing element, and a transparent illuminating body configured to transmit light. The lighting element is arranged subjacent to the housing element which supports the illuminating body. The illumination device is often used as a reading light which can be placed with its illuminating body over a book or other fiat surface configured to be illuminated and viewed via the transparent illuminating body. The illuminating body of the illumination device comprises a light extraction film having a surface structure configured to receive and deflect the light from the lighting element onto the surface to be illuminated. The surface of the illuminating body in the illumination device normally has a sawtooth-like structure. However, since the peak of the sawtooth and the connection parts between the sawteeth are sharp, the pressure applied to these connection parts when the illuminating body is compressed, collides with other parts, or is scratched is much bigger than that on other parts. Therefore, the connection parts can easily be damaged, which may lead to scratches on the illuminating body, which in its turn would further influence the reading effect and shorten the working life of the illumination device. OBJECT AND SUMMARY OF THE INVENTION

It is an object of the invention to provide a light guide plate having a certain scratch resistance. It is a further object of the invention to provide an illumination device using said scratch-resistant light guide plate.

The invention discloses a light guide plate comprising: a first surface, and a second surface; wherein the first and the second surface are substantially parallel to each other, and at least one of the first and the second surface has a surface structure which comprises a plurality of deflection means, each deflection means having an abrupt slope and a gentle slope; the directrixes of the peaks of the deflection means and the valleys between different deflection means being smooth curves. The surface with a surface structure assumes a plane as a whole, because the deflection means have a small size and the gentle slopes have small angles. Consequently, to the naked eye, the surface with a surface structure of the light guide plate looks like a smooth surface.

The invention also discloses an illumination device for illuminating a surface, comprising: a lighting element, an illuminating body, and a housing element; wherein the lighting element emits light; the housing element accommodates the lighting element and supports the illuminating body; and the illuminating body comprises said light guide plate, wherein the deflection means are configured to receive and deflect the light emitted from the lighting element onto the surface to be illuminated.

Because of the smooth structure of the peaks and connection parts in the surface structure of the deflection device, the illuminating body of the illumination device according to the invention, i.e. the light guide plate, has characteristic anti-scratch and anti-abrasion features.

According to one preferred embodiment of the invention, the light guide plate is transparent to the light transmitted internally. Furthermore, the light guide plate is also transparent to the light from its surroundings. This is very important when the light guide plate is used as a reading light. Since the light guide plate is transparent to both the inner light and the light from its surroundings, light emitted to one side of the light guide plate is deflected by the deflection means, and light is emitted from the light guide plate from both the first and the second surface so as to illuminate the plane nearby, such as a book, so that a person can easily look through the light guide plate to see the contents of the book covered by the other side of the light guide plate.

According to one embodiment of the invention, only one of the first and the second surface of the light guide plate has the surface structure comprising deflection means, while the other one is flat and smooth. According to another embodiment of the invention, both the first and the second surface of the light guide plate have the surface structure which comprises the deflection means.

According to a further embodiment of the invention, the gentle slopes of each deflection means of the surface structure on at least one surface of the light guide plate ramp downwards in the same direction, which is the main direction of transmission of the light emitted from the lighting device mounted on one side of the light guide plate.

According to another embodiment of the invention, the surface structure on at least one surface of the light guide plate consists of successively lined up deflection means. In the known prior art, total internal reflection is produced in the light guide plate having the upper surface and the lower surface which are parallel to each other. The surface structure formed by the successively lined up deflection means in this embodiment can change such a condition of total internal reflection, so that the light can be evenly emitted from the first and/or the second surface having such a surface structure, which yields a greater intensity of comfortable illumination onto a plane near the first and/or the second surface. According to a further embodiment of the invention, the angles of the gentle slopes of the deflection means in the surface structure of the light guide plate, i.e. the angles enclosed between the gentle slopes and the first or the second surface of the light guide plate, range between 0.1° and 10°; preferably between 0.2° and 8°; more preferably between 0.5° and 2°.

According to a further embodiment of the invention, the angles of the abrupt slopes of the deflection means in the surface structure of the light guide plate, i.e. the angles enclosed between the abrupt slopes and the first or the second surface of the light guide plate, range between 80° and 90°; preferably between 82° and 88°.

According to another embodiment of the invention, the widths of the deflection means in the surface structure of the light guide plate, i.e. the distances between the bottoms of the gentle slopes and the abrupt slopes of the deflection devices, range between 10 μm and 3 mm; preferably between 50 μm and 1 mm. Since the deflection means have small widths, and the gentle slopes have small angles, the surface with a surface structure of the light guide plate looks like a smooth surface to the naked eye, so that the patterns near the other side of the light guide plate observed through the light guide plate are free from apparent visual distortion.

According to a further embodiment of the invention, the light guide plate has a thickness of between 0.5 mm and 5 mm; preferably between 0.6 mm and 2 mm; more preferably between 0.8 mm and 1.2 mm. A thinner thickness may not only give the light guide plate a lighter weight, but also flexibility to a certain extent, allowing it to bend with the surface to be illuminated.

According to an embodiment of the invention, the light guide plate may comprise one of the following materials: polyethylene, polypropylene, polyamide, polymethyl methacrylate (PMMA), polycarbonate (PC), or polystyrene (PS). As is known, these materials have a good light-admitting quality.

According to one preferred embodiment of the invention, at least a hard mask layer covers the surface structure of the light guide plate. The mask layer often has a greater rigidity than the main material of the light guide plate, which further improves the abrasion resistance of the light guide plate. Optionally, a few other films may cover the hard mask layer, such as one or more antifouling films, antirefiection films and other similar optical films with special effects.

According to a further embodiment of the invention, the deflection means in the surface structure of the light guide plate are constituted by a sawtooth-like or triangular means coated with at least one film, the coating film comprising one hard mask layer. Optionally, the coating film may also comprise other films, such as one or more antifouling films, antirefiection films and other similar optical films with special effects.

According to a further embodiment of the invention, an illumination device comprises a lighting element, an illuminating body, and a housing element, the housing element comprising the lighting element and supporting the illuminating body, which illuminating body may be constituted by any one of the aforesaid light guide plates. The lighting element comprises at least one of a Light Emitting Diode (LED), an Organic Light Emitting Diode (OLED), an incandescent lamp or a fluorescent lamp. In order to achieve a high efficiency and energy conservation, the lighting element in the illumination device preferably uses the LED.

According to a further embodiment of the invention, the illuminating body of the illumination device has a size of less than 600 cm . Considering comfort and convenience of use and the difficulty of production and processing techniques, the illuminating body of the illumination device preferably has a size of less than 400 cm² when the illumination device is used as a reading light. According to another embodiment of the invention, the illumination device further comprises a battery which is used to supply the required electric energy to the lighting element. The illumination device preferably further comprises a solar cell which can convert light energy into electric energy in the illumination surroundings and save the electric energy for use in the dark, so that the illumination device can achieve a more significant conservation of energy.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features , purposes and advantages of the present invention will become apparent from the following detailed description of non-limiting embodiments, given by way of example and described with reference to the accompanying drawings, in which

Fig. 1 is a side view of the light guide plate according to an embodiment of the invention;

Fig. 2 is a side view of the light guide plate according to a further embodiment of the invention;

Fig. 3 is a partially enlarged diagram of a surface structure in the ellipse and dashed part of Fig. 1 and Fig. 2;

Fig. 4 is a partial stereoscopic diagram of the light guide plate according to an embodiment of the invention;

Fig.5 is a sectional side view and a vertical view of the illumination device according to an embodiment of the invention; and

Fig.6 is a side view and a vertical inside view of the illumination device according to another embodiment of the invention.

In the drawings, identical or similar reference numerals indicate identical or similar steps, features or devices (modules). DESCRIPTION OF EMBODIMENTS

Fig. 1 is a side view of the light guide plate 10 according to an embodiment of the invention. The light guide plate 10 substantially assumes the shape of a tabular plate having an upper surface 1 1 and a lower surface 12 which are substantially parallel to each other. In the embodiment shown, the lower surface 12 is fiat and smooth, while the upper surface 11 has a surface structure consisting of a plurality of successively arranged deflection means 21 , each deflection means having an abrupt slope 17 (denoted 17a and 17b in Fig. 1) and a gentle slope 18 (denoted 18a and 18b in Fig. 1). All gentle slopes 18 ramp downwards in the same direction. Although the upper surface 1 1 has a surface structure, it still assumes a plane as a whole when observed with the naked eye, because the deflection means have small sizes and the gentle slopes have small angles. The light guide plate 10 can be used for a reading light so as to illuminate a surface near the light guide plate 10, such as a newspaper or a book. The light is normally emitted by the lighting element 31 on one side of the light guide plate, while the surface structure consisting of the successively lined up deflection means 21 can change the total reflection status inside the light guide plate 10. For instance, light is emitted onto the gentle slope 18a from the inside of the light guide plate 10, with partial light being reflected by the gentle slope 18a towards the lower surface 12, and partial light penetrating the gentle slope 18a mainly by refraction and being emitted from the light guide plate 10. Partial light emitted from the light guide plate 10 by the gentle slope 18a reaches the abrupt slope 17b, wherein at least one part of the light penetrates the abrupt slope 17b and is sent back inside the light guide plate 10. As for the light sent to the lower surface 12 from the inside of the light guide plate 10, part of it is reflected to the upper surface, and part penetrates the lower surface 12 and is emitted from the light guide plate 10. Deflected by the successive deflection means, light is thus emitted from both the upper surface 11 and the lower surface 12 of the light guide plate 10. Outer light can also penetrate the light guide plate 10, so that a person can look through the light guide plate 10 and can see the contents of the page covered by the light guide plate 10. The angles of the gentle slopes, i.e. the angles enclosed between every gentle slope and the upper surface 11 or the lower surface 12 can be changed. For instance, the respective angles of the gentle slopes 18a and 18b may be the same or different; likewise, the angles of the abrupt slopes, i.e. the angles enclosed between every abrupt slope and the upper surface 11 or the lower surface 12 may be changed. For instance, the respective angles of the abrupt slopes 17a and 17b may be the same or different, so that the light emitted from the light guide plate 10 can achieve a better optical distribution.

Fig. 2 is a side view of the light guide plate 10' according to a further embodiment of the invention. The light guide plate 10' substantially assumes the shape of a tabular plate having an upper surface 1 1 and a lower surface 12 which are substantially parallel to each other. In the embodiment shown, the upper surface 11 has a surface structure which is constituted by a plurality of successively arranged deflection means 21 , each deflection means 21 having an abrupt slope 17 and a gentle slope 18. The lower surface 12 also has a surface structure which is constituted by a plurality of successively arranged deflection means 22, each deflection means 22 having an abrupt slope 17 and a gentle slope 18. All gentle slopes 18 ramp downwards in the same direction. The light is normally emitted by the lighting element 31 on one side of the light guide plate, while the surface structure formed by the deflection means 21 and 22 can change the total reflection status inside the light guide plate 10'. Through deflection of the successive deflection means, light is emitted from the upper surface 11 and the lower surface 12 of the light guide plate 10'. The angles of the gentle slopes can be changed. Likewise, the angles of the abrupt slopes can also be changed, so that the light emitted from the light guide plate 10' can achieve a better optical distribution. Fig. 3 is a partially enlarged diagram of the surface structure in the ellipse and dashed part of Fig. 1 and Fig. 2. As shown, the surface structure consists of successive deflection means 21 each having an abrupt slope 17 and a gentle slope 18. The directrixes of a deflection means can be approximately divided into four parts, as shown in Fig. 3, i.e. connection part A between the gentle slope 18a of the deflection means 21a and the abrupt slope 17b of deflection means 21b, peak part C of deflection means 21b, and respective parts B and D to which the abrupt slope 17b and the gentle slope 18b of the deflection means 21b correspond. Parts B and D are substantially straight lines, while parts A and C are substantially smooth curves. The peak part of each deflection means is easily subject to scratches, collisions or other external forces. In this embodiment, the peak part of each deflection means and the connection parts between different deflection means are streamlined. Therefore, when an external force is exerted thereon, the pressure can be partially distributed to decrease local pressure, so that the deflection means cannot be easily damaged, while the light guide plate 10 has characteristic anti-scratch and anti-abrasion features and still has good reading and viewing effects, even after repeated use.

At least a hard mask layer preferably covers the surface structure, which may further improve the characteristic anti-scratch and anti-abrasion features of the light guide plate 10. A few other films may preferably cover the hard mask, such as one or more antifouling films, antireflection films and other similar optical films with special effects giving the light guide plate an improved performance as regards antifouling and antireflection, etc. Normally, the antifouling film is applied as the uppermost layer, while the antireflection film can be applied on or under the hard mask layer.

As shown in Fig. 3, the angle of abrupt slope 17 of the deflection means is α, and the angle of gentle slope 18 of the deflection means is β. Normally, the angle β of gentle slope 18 ranges between 0.1° and 10°, preferably between 0.5° and 8°. Normally, the angle of abrupt slope 17 α ranges between 80° and 90°, preferably between 82° and 88°. Normally, the width of the deflection means, i.e. the distance between the bottom of the abrupt slope 17 and that of the gentle slope 18 is between 10 μm and 3 mm, preferably between 50 μm and 1 mm. Since the deflection means 21 has a small width, the upper and the lower surface of the light guide plate 10 look like two smooth surfaces to the naked eye. Since the gentle slope 18 has a small angle, the patterns near the light guide plate observed by a person looking through the light guide plate 10 are free from apparent visual distortion.

The material of which the light guide plate 10 is made may be the usual chemical raw materials, such as polyethylene, polyamide, polypropylene, polymethyl methacrylate (PMMA), polycarbonate (PC) or polystyrene (PS). As is known, these materials have a good light-admitting quality.

The light guide plate of the invention can be produced by means of two methods.

One method is direct injection molding, using materials such as PMMA and PC, etc. to produce the light guide plate of the invention. In accordance with different purposes and requirements, a few films preferably cover the surface of the light guide plate.

The other method comprises a first step of producing a light guide plate having a surface structure on at least one surface, the surface structure comprising a plurality of deflection means having a cross-section such as a sawtooth, a triangle, a trapezium or other similar shapes. Fig. 4(1) illustrates one type of such a surface structure of the deflection means having the cross-section of a sawtooth or a triangle. The method further comprises a second step of coating a mask on the surface structure produced in the first step, as shown in Fig. 4(2), wherein the mask can form the approximately cylindrical surface and has curvilinear directrixes on the corners so as to produce the light guide plate disclosed by the invention. The method of coating the mask may be dip-coating, spin-coating, spray-coating, flow-coating or any other method. The material rigidity of the mask should be preferably higher than that of the surface structure in the first step so as to give the light guide plate its characteristic anti-scratch and anti-abrasion features. More preferably, the hard mask can be covered with a few other films, such as one or more antifouling films, antirefiection films and other similar optical films with special effects giving the light guide plate an improved performance as regards antifouling and antirefiection, etc. Normally, the antifouling film is applied as the uppermost layer, while the antirefiection film can be applied on or under the hard mask layer.

Fig.5 is a sectional side view and a vertical view of the illumination device 9 according to an embodiment of the invention. The illumination device 9 comprises lighting element 31, illuminating body 20, and housing element 40. The lighting element 31 is mounted inside the housing element 40 which is also used to support the illuminating body 20. In the embodiment shown, the illumination device 9 is a reading light which is used to illuminate a surface under the illuminating body 20, such as a newspaper or a book. This illuminating body 20 can adopt the light guide plate 10 or 10'. A plurality of deflection means 21 on the upper surface of the illuminating body 20 are used to receive and deflect the light emitted from the lighting element 31 onto the surface to be illuminated.

The lighting element 31 comprises a few LEDs which are normally mounted on the side of the illuminating body 20. If these few LEDs do not have a sufficient light intensity, a plurality of LEDs can be mounted on the side of the illuminating body 20. The lighting element 31 connects to the housing element 40 which may comprise a Printed Circuit Board (PCB). The LEDs can directly connect to the electronic device on the Printed Circuit Board. A battery 61 and a driving device 62 are mounted in the housing element 40. The battery 61 , which is preferably rechargeable, is used to supply the required electric current to the lighting element 31. The driving device 62 may comprise a current amplifier and a waveform generation and control circuit, which circuit is used to generate the desired waveform to drive the lighting element 31 and is also used to adjust the amplitude, frequency and duty cycle of the waveform. The housing element 40 may also be provided with a switch which is used to control the operation of the lighting element 31.

In order to render the illumination device 9 optically more power efficient, the housing element 40 can be provided with a solar cell 60. In the surroundings of illumination, the solar cell 60 can convert light energy into electric energy and save it in the rechargeable battery 61 , so that the illumination device 9 can be used for illumination in the dark.

The lighting element 31 may be a LED, an OLED, an incandescent lamp or a fluorescent lamp. Since the LED can supply sufficient light intensity with a lower power consumption, it is better to use a LED. The lighting element 31 in the illustrated embodiment is a LED.

In the embodiment shown, the illuminating body 20 in the illumination device 9 has a size of 10 cmx l5 cm. If used as a hand-held reading light, the illuminating body 20 in the illumination device 9 should have a moderate size. Other typical sizes may include 5 cm* 10 cm, 12 cmx20 cm, etc. In the embodiment shown, the illuminating body 20 in the illumination device 9 has a thickness of about 1 mm. In order to ensure the degree of comfort of viewing and reading by means of the reading light, the illuminating body 20 is generally preferred to have a thickness of less than 5 mm. If used as an illumination device in a display window or for other purposes, the illuminating body 20 in the illumination device 9 may even have a size of more than 1 m .

Fig.6 is a side view and a vertical inside view of the illumination device 9' according to another embodiment of the invention. In this embodiment, lighting element 31 is a LED, and, as shown in Fig. 6, a plurality of LEDs are arranged along the side of the illuminating body 20 so as to provide a relatively uniform light source supplying sufficient light. In the illumination device 9', a solar cell 60 is mounted on the illuminating body 20. Generally, the solar cell 60 has a size which may be equal to or less than that of the illuminating body 20. In order to be used as a reading light, the solar cell 60 should also be transparent to the light emitted by the lighting element 31 or the light in its surroundings. As compared with the illumination device 9 shown in Fig. 5, the illumination device 9' in this embodiment has the advantage that the volume of the housing element 40 can be decreased considerably, because the solar cell is arranged on the illuminating body 20 rather than on the housing element 40.

The invention is neither limited to the embodiments of the invention described hereinbefore, nor to certain systems, devices and materials. Those skilled in the art will be able to make various changes or modifications without departing from the scope of the appending claims.

LIST OF REFERENCE NUMERALS

8 air;

10 light guide plate;

11 first surface;

12 second surface;

17 abrupt slope;

18 gentle slope;

20 illuminating body; 21 ,22 deflection means;

31 lighting element;

60 solar cell;

61 battery;

62 driving device.

Claims

1. A light guide plate (10) comprising: a first surface (11); and a second surface (12); wherein the first and the second surface are substantially parallel to each other, and at least one of the first and the second surface has a surface structure which comprises a plurality of deflection means (21), each deflection means having an abrupt slope (17) and a gentle slope (18); the directrixes of the peaks of the deflection means and the valleys between different deflection means being smooth curves.

2. A light guide plate according to claim 1, wherein all gentle slopes ramp downwards in the same direction.

3. A light guide plate according to claim 1 or 2, wherein the surface structure consists of successively lined up deflection means.

4. A light guide plate according to claim 1 or 2, wherein the gentle slopes have angles ranging between 0.1° and 10°.

5. A light guide plate according to claim 1 or 2, wherein the abrupt slopes have angles ranging between 80° and 90°.

6. A light guide plate according to claim 1 or 2, wherein each deflection means has a width of between 10 μm and 3 mm.

7. A light guide plate according to claim 1 or 2, comprising one of the following materials: polyethylene, polyamide, polypropylene, polymethyl methacrylate (PMMA), polycarbonate (PC), or polystyrene (PS).

8. A light guide plate according to claim 1 or 2, wherein the deflection means is constituted by a sawtooth-like means and at least one coating film.

9. A light guide plate according to claim 8, wherein the coating film comprises a stiffened coating film and/or at least one of an antifouling film, or an antireflection film.

10. An illumination device (9) for illuminating a surface, comprising: a lighting element (31), an illuminating body (20), and a housing element (40); wherein the lighting element emits light, the housing element accommodates the lighting element and supports the illuminating body; and the illuminating body comprises a light guide plate of any one of claims 1 to 9, wherein the deflection means are configured to receive and deflect the light emitted from the lighting element onto the surface to be illuminated.

11. An illumination device according to claim 10, wherein the lighting element comprises at least one of a Light Emitting Diode, an Organic Light Emitting Diode, an incandescent lamp, or a fluorescent lamp.

12. An illumination device according to claim 10 or 11, wherein the illuminating body has a size of less than 600 cm².

13. An illumination device according to claim 10 or 11, wherein the illumination device further comprises a solar cell (60) and/or a battery (61).