GB2281802A - Illumination apparatus - Google Patents

Illumination apparatus Download PDF

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Publication number
GB2281802A
GB2281802A GB9416666A GB9416666A GB2281802A GB 2281802 A GB2281802 A GB 2281802A GB 9416666 A GB9416666 A GB 9416666A GB 9416666 A GB9416666 A GB 9416666A GB 2281802 A GB2281802 A GB 2281802A
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Application
Patent type
Prior art keywords
surface
light
illumination apparatus
illumination
apparatus according
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB9416666A
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GB9416666D0 (en )
Inventor
Eddie Hattersley
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Simrad Stowe Ltd
Original Assignee
* SIMRAD STOWE LIMITED
SIMRAD STOWE LIMITED
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date

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Classifications

    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B6/00Light guides
    • G02B6/0001Light guides specially adapted for lighting devices or systems
    • G02B6/0011Light guides specially adapted for lighting devices or systems the light guides being planar or of plate-like form
    • G02B6/0033Means for improving the coupling-out of light from the light guide
    • G02B6/0035Means for improving the coupling-out of light from the light guide provided on the surface of the light guide or in the bulk of it
    • G02B6/0045Means for improving the coupling-out of light from the light guide provided on the surface of the light guide or in the bulk of it by shaping at least a portion of the light guide
    • G02B6/0046Tapered light guide, e.g. wedge-shaped light guide
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B6/00Light guides
    • G02B6/0001Light guides specially adapted for lighting devices or systems
    • G02B6/0011Light guides specially adapted for lighting devices or systems the light guides being planar or of plate-like form
    • G02B6/0033Means for improving the coupling-out of light from the light guide
    • G02B6/0035Means for improving the coupling-out of light from the light guide provided on the surface of the light guide or in the bulk of it
    • G02B6/00362-D arrangement of prisms, protrusions, indentations or roughened surfaces
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B6/00Light guides
    • G02B6/0001Light guides specially adapted for lighting devices or systems
    • G02B6/0011Light guides specially adapted for lighting devices or systems the light guides being planar or of plate-like form
    • G02B6/0066Light guides specially adapted for lighting devices or systems the light guides being planar or of plate-like form characterised by the light source being coupled to the light guide
    • G02B6/0068Arrangements of plural sources, e.g. multi-colour light sources

Abstract

Illumination apparatus for a liquid crystal display includes a reflector which is shaped or patterned so that the intensity of light reflected from different parts of the reflector is varied thereby obtaining uniform illumination. In one embodiment an edge illuminated device includes a wedge shaped plate 18 which is frosted at its lower surface, the frosting being greatest at the thick end of the plate. Light from the sources 52 is internally reflected within the plate 18 until it strikes a surface deformity on the frosted surface whereupon it is either reflected upwardly or downwards towards a reflector sheet 16. <IMAGE>

Description

ILLUMINATION APPARATUS The present invention relates to an illumination apparatus. It has particular utility in the backlighting of a flat screen liquid crystal display.

In recent years liquid crystal displays have become a popular device for providing an interface between an electronic device and its user. One reason for this popularity is the thinness of a liquid crystal display. Often, this means that a display can be provided on an electronic device without significantly increasing the volume of that device, or affecting the external design of that device. However, liquid crystal displays do have some disadvantages.

In particular, such displays are of a passive nature (i.e. they do not output any light) and rely for their operation on the presence of ambient light. It is therefore common practice to supply a liquid crystal display with an auxiliary light which can be activated by the user in low level lighting conditions. In order to preserve the advantage of the thinness of the display and provide an auxiliary light, it is known to place a planar illumination apparatus behind the liquid crystal display window. Typically, such an apparatus is placed in the narrow planar region between the circuitry of the instrument and the LCD glass.It is known for these planar illumination apparatuses to comprise a substantially flat, shaped piece of acrylic which is illuminated on one side by a discrete light source and which redistributes the light through its upper surface and on through a liquid crystal display. Examples of such systems can be seen in European Patent Application EP-A-495273 and United Kingdom Patent Application GB-2247536A.

As stated in the latter patent application a problem arises with the use of discrete light sources in that the illumination provided to the display is uneven, with areas of relatively high brightness ("hot spots") close to the discrete light sources. One solution that has been proposed to this problem is suggested in EP-A-495273. This solution is to provide a flat piece of acrylic with an prismatic surface which has surface deformities of varying depth to cause more light to be reflected from some regions than others. However, the manufacture of such pieces of acrylic is both complex and expensive. The present invention is intended to provide a simple and inexpensive illumination apparatus for providing a predetermined distribution and light to a liquid crystal display.In particular the invention may provide a simple and cost-effective apparatus for evenly illuminating a liquid crystal display.

According to the present invention there is provided an illumination apparatus comprising; at least a first light source; a light diffusing plate having an illumination surface; a reflector means for reflecting light towards the illumination surface, and adapted to provide a predetermined variation in the intensity of the light reflected towards different parts of said illumination surface; the arrangement being such that light from said first light source is incident on said light diffusing plate; at least a portion of the light from the first light source is reflected by said reflector means before being transmitted from said illumination surface, the intensity of light transmitted from different parts of the illumination surface being at least partly determined by the reflection from said reflector means.

It will be seen, therefore, how the present invention, by decreasing the amount of light reflected by the reflector in the region in the hot spots, may provide even illumination over a planar area.

Advantageously, the reflector means is provided by a sheet of material which has a surface with a predetermined variation in its reflectivity. The advantage of this is that such a sheet of material can be cheaply and easily manufactured. Advantageously, the sheet of material is provided by a printed sheet of card, the predetermined variation in reflectivity being provided by the printing on the card. It will be appreciated that printing is a simple and relatively inexpensive way of creating a predetermined variation in the reflectivity of the sheet.

In a preferred embodiment, the reflector means has a surface whose reflectivity is constant over its area. In this case, the predetermined variation in the intensity of the light reflected towards different parts of the illumination surface is provided by giving the reflector a predetermined shape. This has the advantage of avoiding even the expense of printing onto the reflector and hence further reduces the unit production cost of the apparatus.

The invention will now be described further with reference to and as illustrated in the accompanying drawings in which: Figure 1 is an exploded perspective view of a panel illumination apparatus of a first embodiment of the present invention, Figure 2 is a front elevational view of a liquid crystal display incorporating the panel illumination apparatus illustrated in Figure 1, and Figure 3 is a view similar to Figure 1, but showing a preferred embodiment of the present invention.

Referring now to Figure 1, a panel illumination apparatus comprises a central planar section, indicated generally at (10), and two light sources (12, 14) disposed alongside two parallel peripheral edges (28, 29) of the central planar section (10). The central planar section (10) comprises three parts, namely a diffusing sheet (20) which is situated on top of a grooved acrylic plate (18) which in turn is situated on top of a reflecting sheet (16). Each light source (12, 14) comprises an incandescent bulb (30, 32), which is bounded on its outside by a reflector (34, 36). Each reflector (34, 36) is formed from a sheet of metal which has been bent to form a channel of a substantially constant V-shaped cross-section.

The acrylic plate (18) is formed from a rectangular block of acrylic material which has an upper major surface (24), a lower major surface (25), and four peripheral surfaces (26, 27, 28, 29). The lower major surface (25) is provided with a series of elongate grooves of triangular cross-section (22) running parallel to the peripheral edges (28, 29).

The surfaces of the grooves (22) are finely roughened, whereas all the other surfaces of the acrylic block are polished to promote internal reflection of light inside the plate (18).

The reflecting sheet (16) has a series of lines (40) printed thereon. These lines are spaced relatively closely near the peripheral edges of the reflecting sheet, and further apart towards the centre of the sheet (16).

In operation, light from the light sources (12, 14) enters the acrylic block (18) via the peripheral edges (28, 29) and is internally reflected off the major surfaces of that block until it strikes a groove (22), whereupon it is either reflected upwards through the upper major surface (24) of the block or is refracted downwards towards the reflecting sheet (16) where it may be reflected back upwards through the major upper surface (24). Since a proportion of the light passing downwards to the reflecting surface will be absorbed by striking the lines (40) it is clear the regions in which the lines are most closely spaced will reflect less light through the upper surface (24).Hence, the effect of any "hot spots" in the panel illumination can be corrected by increasing the density of lines printed on the parts of the reflective sheet (16) lying beneath those parts of the block (18) where the "hot spots" occur. Thus, the printing of the lines in the manner described above tends to correct for the bright region that typically occurs close to the light sources (12, 14).

The light reflected from each groove (22) forms a narrow band of light extending upwards towards the diffuser (20). The spacing of the grooves (22) is selected so that each narrow band of light is diffused sufficiently to overlap with the light emanating from a neighbouring groove.

Referring now to Figure 2 which shows the panel illumination apparatus being used to illuminate an LCD display of an electronic instrument, the apparatus is fitted into the narrow planar gap between a printed circuit board (50) of the instrument and a liquid crystal display screen (60).

Although the purpose of the above described embodiment is to provide an even illumination over an extended area, it is envisaged that a predetermined light distribution might be provided. For example, if a decreased density of lines were provided underneath a particular region of the display, that part of the display would be brighter than the surrounding display, and hence any information displayed in that part of the display would be emphasized.

The markings on the card may be of any shape, shade or colour.

A preferred embodiment of the present invention is shown in Figure 3. It will be seen that the preferred embodiment includes the same principal features as those of the first embodiment in that it comprises a light diffusing plate (18) sandwiched between the diffusing sheet (20) and a reflecting sheet (16) with a light source (indicated generally at (51)) directing light to a peripheral edge of the light diffusing plate (18). Again, it will be seen that the apparatus is adapted to be placed in the narrow planar gap between the body of a device and a display to be illuminated. For the ease of the following description it will be assumed that the apparatus of the preferred embodiment is orientated horizontally, the illumination being provided by the apparatus on its upper side, and a light source being disposed alongside the left hand peripheral edge of the light diffusing plate.

The light diffusing plate (18) generally has the shape of a rectangular slab, having an upper surface (24), a lower surface (25), and four peripheral surfaces, namely a left hand peripheral surface (29), a front peripheral surface (27), a right hand peripheral surface (28) and a rear peripheral surface (not shown). The depth of the plate (18) decreases from the left hand edge (29) to the right hand edge (28) to give the plate (18) the shape of a wedge.

Frosting is applied to the lower surface of the wedge (25), the degree of this frosting decreasing from a relatively heavy frosting towards the left hand peripheral side (29) of the wedge to a relatively light frosting at the opposite end of the wedge adjacent to the right hand peripheral surface (28).

The light diffusing plate (18) is formed from a colourless transparent material such as acrylic and each of the surfaces is polished save for the frosted surface (25).

A diffusing sheet (20) of similar horizontal dimensions to the light diffusing plate (18) is provided directly above and parallel to the plate (18). This diffusing sheet is formed of transluscent matt paper.

A rectangular reflector sheet (16) is provided directly underneath the light diffusing plate (18) and is of a similar length to the light diffusing plate (18) but has a width which is a distance X shorter than the width of the light diffusing plate (18). The sheet (16) is provided with a surface of uniform reflectivity.

Finally, the light source, (shown generally at (51)) is provided by a number of LED's (52). The LED's (52) are arranged at equally spaced intervals in a straight line running parallel to the left hand peripheral edge (29) of the plate (18). Each LED is provided with its own reflector and is orientated to emit light towards the left hand peripheral edge (29).

In operation, light from the LED's (52) is directly incident on the left hand peripheral edge of the light diffusing plate (18), where it is internally reflected until its angle of incidence with the surface of the plate (18) falls below the critical angle to the acrylic material which makes up the plate (18).

The heavy frosting applied to the lower surface (25) in the region close to the light source (52) results in the light incident on the left-hand edge being scattered in various directions.

Experiments by the present inventors have shown that if no frosting is applied to the lower surface (25), then a "hot spot" is seen at the left hand edge of the wedge adjacent to each individual light source.

Furthermore, in a region close to the left-hand edge, light and dark bands running parallel to the left hand peripheral surface (29) of the wedge are seen. These effects are markedly reduced by the presence of the heavy frosting on the plate (18) of the present embodiment. However, in order to ensure that a reasonable amount of light is emitted from the right-hand side of the wedge, lighter frosting is applied to the wedge away from the region close to the left-hand peripheral surface (29) of the wedge.

In addition, the angle of incidence of the rays with the frosted surface (25) will be highly variable and a proportion of the light will consequently be refracted downwards from the plate (18) and another portion of the light will be reflected upwards towards the illumination surface (24) of the plate (18).

Those rays which are refracted from the lower surface (25) at a greater distance than X from the left hand edge of the plate (18) may be reflected by the reflecting plate (16) through the plate (18) to the illumination surface. However, those light rays which were refracted from the lower surface (25) at a distance less than a distance X from the left hand edge of the plate (18) may not be reflected and hence any "hot-spot" caused by the proximity of the left hand edge of the plate (18) to the light source and also by the heaviness of the frosting adjacent the left hand edge of the plate (18) will be at least partly corrected for by the absence of the reflector plate (16) from this region.

It will be seen how this embodiment removes the need for two light sources, one on either side of the light diffusing plate (18), by providing the wedge shape to the plate (18). It will also be seen that the tapering of the plate towards its right hand edge (28) causes light to be reflected towards the illumination surface (24) rather than escaping through the right hand side of the plate (18).

Furthermore, it will be seen that the provision of a reflecting plate of a particular shape obviates the need for providing a surface whose reflectivity varies over its area and therefore obviates the need for printing step in the manufacture of the device and hence reduces the unit production cost of the device.

The second embodiment described is to be preferred because a frosted surface can be more easily, repeatably, and cheaply provided than can the grooved surface in the first embodiment described.

In addition, the man skilled in the art will appreciate that many types of light sources could be used, for instance, fluorescent strip lights could be used for larger display areas. Fluorescent strip lights and the like will preferably be provided with a back reflector. In addition, it will be appreciated that if a reflector is provided then that may be of many different shapes so long as it reflects stray light from the light towards the acrylic plate.

It can be seen how the apparatus of the present invention provides a simple and inexpensive way of providing a predetermined light distribution pattern over a surface, without necessitating the use of intricately shaped light distribution means.

Claims (16)

1. An illumination apparatus comprising; at least a first light source; a light diffusing plate having an illumination surface; a reflector means for reflecting light towards the illumination surface, and adapted to provide a predetermined variation in the intensity of the light reflected towards different parts of said illumination surface; the arrangement being such that light from said first light source is incident on said light diffusing plate; at least a portion of the light from the first light source is reflected by said reflector means before being transmitted from said illumination surface, the intensity of light transmitted from different parts of the illumination surface being at least partly determined by the reflection provided by said reflector means.
2. An illumination apparatus according to claim 1 wherein: said reflecting means has a reflecting surface, the reflectivity of which varies in a predetermined manner over its area to provide said predetermined variation.
3. An illumination apparatus according to claim 1 wherein: said reflecting means is shaped to provide said predetermined variation.
4. An illumination apparatus according to claim 1 wherein: the light diffusing plate is provided with a second surface opposite said illumination surface; and said second surface is shaped to reflect light towards said illumination surface.
5. An illumination apparatus according to claim 4 wherein: said second surface is frosted.
6. An illumination apparatus according to claim 5 wherein: the degree of frosting applied to said second surface varies over said second surface.
7. An illumination apparatus according to claim 1 or claim 5 wherein: said light diffusing plate is wedge-shaped; and light from said light source is coupled to the thick end of said light diffusing plate.
8. An illumination apparatus according to claim 7 wherein: a greater degree of frosting is applied to said second surface adjacent the thick end of the wedge then is applied to said second surface adjacent to the thin end of the wedge.
9. An illumination apparatus according to claim 2 wherein: the reflector means is provided by a sheet of material.
10. An illumination apparatus according to claim 9 wherein: the sheet of material comprises a printed sheet of card, the predetermined variation in the reflectivity being provided by printing on the card.
11. An illumination apparatus according to claim 1 wherein: said light diffusing plate has at least a peripheral surface and a second surface of greater area than said peripheral surface; and said first light source is disposed alongside the peripheral surface.
12. An illumination apparatus according to any preceding claim wherein: a diffuser means is provided between the illumination surface of the plate and the area to be illuminated.
13. An illumination apparatus according to claim 12 wherein: said diffuser means is provided by a sheet of translucent matt paper.
14. A liquid crystal display comprising a diffuse illumination apparatus according to any preceding claim, a liquid crystal display window, the arrangement being such that the light transmitted from the diffuse light source passes through the liquid crystal display glass.
15. An illumination apparatus substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2.
16. An illumination apparatus substantially as hereinbefore described with reference to and as illustrated in Figure 3.
GB9416666A 1993-08-17 1994-08-17 Illumination apparatus Withdrawn GB9416666D0 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB9317086A GB9317086D0 (en) 1993-08-17 1993-08-17 Planar illumination apparatus

Publications (2)

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GB9416666D0 GB9416666D0 (en) 1994-10-12
GB2281802A true true GB2281802A (en) 1995-03-15

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GB9317086A Pending GB9317086D0 (en) 1993-08-17 1993-08-17 Planar illumination apparatus
GB9416666A Withdrawn GB9416666D0 (en) 1993-08-17 1994-08-17 Illumination apparatus

Family Applications Before (1)

Application Number Title Priority Date Filing Date
GB9317086A Pending GB9317086D0 (en) 1993-08-17 1993-08-17 Planar illumination apparatus

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1997022905A1 (en) * 1995-12-19 1997-06-26 Polaroid Corporation Efficient led light geometry for optical printers
WO1998036315A1 (en) * 1997-02-13 1998-08-20 Alliedsignal Inc. Illumination system with light recycling to enhance brightness
EP0879991A2 (en) * 1997-05-13 1998-11-25 Matsushita Electric Industrial Co., Ltd. Illuminating system
EP1522881A1 (en) * 2003-10-06 2005-04-13 Omron Corporation Surface light source device and display device
WO2009068285A1 (en) * 2007-11-27 2009-06-04 Johnson Controls Gmbh Optical arrangement
US9625633B2 (en) 2003-06-23 2017-04-18 Rambus Delaware Llc Light emitting panel assemblies

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4618216A (en) * 1980-03-24 1986-10-21 Seiko Epson Kabushiki Kaisha Backlighted liquid crystal display using light passage member for more nearly uniform illumination
US4673254A (en) * 1985-07-30 1987-06-16 Tokyo Keiki Co., Ltd. Back-reflection type light diffusing apparatus
GB2238377A (en) * 1989-09-30 1991-05-29 Meitaku Syst Kk Surface luminous source panel
US5130898A (en) * 1989-05-18 1992-07-14 Seiko Epson Corporation Background lighting apparatus for liquid crystal display
EP0501761A2 (en) * 1991-02-27 1992-09-02 Sharp Kabushiki Kaisha Apparatus for lighting of liquid crystal display
GB2267378A (en) * 1992-05-22 1993-12-01 Nokia Mobile Phones Uk Illuminated liquid crystal displays

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4618216A (en) * 1980-03-24 1986-10-21 Seiko Epson Kabushiki Kaisha Backlighted liquid crystal display using light passage member for more nearly uniform illumination
US4673254A (en) * 1985-07-30 1987-06-16 Tokyo Keiki Co., Ltd. Back-reflection type light diffusing apparatus
US5130898A (en) * 1989-05-18 1992-07-14 Seiko Epson Corporation Background lighting apparatus for liquid crystal display
GB2238377A (en) * 1989-09-30 1991-05-29 Meitaku Syst Kk Surface luminous source panel
EP0501761A2 (en) * 1991-02-27 1992-09-02 Sharp Kabushiki Kaisha Apparatus for lighting of liquid crystal display
GB2267378A (en) * 1992-05-22 1993-12-01 Nokia Mobile Phones Uk Illuminated liquid crystal displays

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1997022905A1 (en) * 1995-12-19 1997-06-26 Polaroid Corporation Efficient led light geometry for optical printers
US5969747A (en) * 1995-12-19 1999-10-19 Polaroid Corporation Efficient LED light geometry for optical printers
WO1998036315A1 (en) * 1997-02-13 1998-08-20 Alliedsignal Inc. Illumination system with light recycling to enhance brightness
US6144536A (en) * 1997-02-13 2000-11-07 Honeywell International Inc. Illumination system with light recycling to enhance brightness
EP0879991A2 (en) * 1997-05-13 1998-11-25 Matsushita Electric Industrial Co., Ltd. Illuminating system
EP0879991A3 (en) * 1997-05-13 1999-04-21 Matsushita Electric Industrial Co., Ltd. Illuminating system
US6379017B2 (en) 1997-05-13 2002-04-30 Matsushita Electric Industrial Co., Ltd. Illuminating system
US9625633B2 (en) 2003-06-23 2017-04-18 Rambus Delaware Llc Light emitting panel assemblies
US9983340B2 (en) 2003-06-23 2018-05-29 Rambus Delaware Llc Light emitting panel assemblies
EP1522881A1 (en) * 2003-10-06 2005-04-13 Omron Corporation Surface light source device and display device
US7162139B2 (en) 2003-10-06 2007-01-09 Omron Corporation Surface light source device and display device
WO2009068285A1 (en) * 2007-11-27 2009-06-04 Johnson Controls Gmbh Optical arrangement

Also Published As

Publication number Publication date Type
GB9317086D0 (en) 1993-09-29 grant
GB9416666D0 (en) 1994-10-12 grant

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