WO2007105149A1

WO2007105149A1 - Backlight reflector

Info

Publication number: WO2007105149A1
Application number: PCT/IB2007/050751
Authority: WO
Inventors: Paulus G. H. Kosters
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2006-03-15
Filing date: 2007-03-07
Publication date: 2007-09-20

Abstract

The invention relates to a backlight illumination system (10) which comprises a plurality of linear light sources (20) arranged substantially parallel to each other sandwiched between a reflector (40) and a light-exit window (30). The reflector (40) is arranged for reflecting light emitted by the light sources (20) away from the light-exit window (30) back towards the light-exit window (30). The reflector (40) comprises a reflective region for each of the light sources (20). Each reflective region comprises a first reflective surface (70) which has a concave shape with respect to the light source (20). The shape of the first reflective surface (70) is defined by a curve (61) where a reflector tangent (62) arranged tangentially to the curve (61) at a particular point on the curve (61) is arranged perpendicular to a source tangent (64) arranged tangential to a light-exit wall (24) of the linear light source (20) and intersecting the particular point. The effect of the shape of the first reflective surface (70) is that substantially all light emitted by the linear light source (20) away from the light-exit window (30) is reflected back to the light-exit window (30) while the reflected light is prevented from impinging on the linear light source (20). This increases the efficiency of the backlight illumination system (10).

Description

Backlight reflector

FIELD OF THE INVENTION:

The invention relates to a backlight illumination system comprising a reflector for reflecting light emitted by a linear light source towards the light-exit window of the backlight illumination system. The invention also relates to a display device comprising the backlight illumination system.

BACKGROUND OF THE INVENTION:

Illumination systems which comprise a reflector for reflecting light emitted by a light source towards the light-exit window of the illumination system are known per se. They are used, inter alia, as backlighting of (image) display devices, for example for television receivers and monitors. Such illumination systems can particularly suitably be used as a backlight for non-emissive displays, such as liquid crystal display devices, also referred to as LCD panels, which are used in (portable) computers, (cordless) telephones or remote- control units. Another application area of the illumination system according to the invention is the use as illumination source in a digital projector or so-called beamer for projecting images or displaying a television program, a film, a video program or a DVD, or the like. In addition, such illumination systems are used for general lighting purposes, such as for large-area direct-view light emitting panels such as applied, for instance, in signage, contour lighting, and billboards.

The illumination system comprises a plurality of linear light sources and a plurality of reflectors. The plural linear light sources are arranged in parallel at predetermined intervals facing a light-exit window of the backlight illumination system. The plurality of linear light sources can also be embodied in a single light source comprising a collection of parallel straight parts, which straight parts are connected together by means of bent parts. An example of such an "integral" light source is a so-called compact cold-cathode fluorescent meander lamp.

The reflector in the illumination system is, generally, in the shape of a symmetrical continuous "wave" and is disposed at a side of the light sources facing away from the light-exit window. Part of the reflector can be arranged in between the light sources. Part of the light emitted by the light sources is directly incident on the light-exit window, other parts of the light emitted by the light sources is reflected by the reflector and reflected towards the light-exit window. In general, the reflector is made of a thin sheet of a specular reflective material. The sheet is shaped by means of bending or curving or otherwise. Each of the reflective surfaces reflects light back to the light-exit window.

US Patent Application Publication US-A 2003/0058635 discloses a backlight illuminator including a reflector for each of linear light sources arranged in parallel at predetermined intervals. The reflector includes a reflective region formed symmetrically about each light source. In one half part of symmetry, the reflective region comprises three reflective surfaces including a reflective surface close to the light source, an intermediate reflective surface, and a reflective surface distant from the light source. The reflective surface close to the light source is formed to have a flat horizontal reflective surface to reflect light back to a relatively wide range of surface to be illuminated. The intermediate reflective region is formed to have a curved reflective surface concavely curved thereto so as to have reflected light overlapped with reflective light illuminating in the wide range of the surface to be illuminated. The reflective region distant from the light source is formed to have a reflective surface slanted to the horizontal reflective surface so as to have reflected light overlapped with reflected light illuminating in the wide range of the surface to be illuminated.

A drawback of the known illumination system is that the known illumination system does not provide optimum efficiency.

SUMMARY OF THE INVENTION: It is an object of the invention to provide a backlight illumination system having improved efficiency.

According to a first aspect of the invention the object is achieved with a backlight illumination system comprising: a plurality of linear light sources arranged substantially parallel to each other, each light source having a longitudinal axis and a light-exit wall arranged around the longitudinal axis, a light-exit window arranged between the plurality of light sources and the display device and arranged substantially parallel to the plurality of light sources for emitting light towards the display device, and a reflector arranged at a side of the light sources facing away from the light- exit window for reflecting light emitted by the linear light source towards the light-exit window, the reflector comprising a reflective region for each of the light sources, the respective reflective regions being formed in symmetry with respect to a first imaginary plane through the longitudinal axis of each of the light sources, the first imaginary plane being arranged substantially perpendicular to the light-exit window, each reflective region extending substantially parallel to the light sources, each reflective region comprising: a first reflective surface being concavely shaped with respect to the light source defined by a curve in a second imaginary plane that is arranged perpendicular to the longitudinal axis, the curve starting at a starting point and extending from the starting point in a direction of a side of the light source facing away from the light-exit window, each point of the curve being defined by a reflector tangent that is arranged substantially perpendicular to a source tangent, the reflector tangent being arranged tangential to the curve at each respective point, the source tangent intersectingthe respective point and being arranged tangential to the light-exit wall, the starting point being located on a starting tangent intersectingan intersection between the first imaginary plane and the light-exit window and being arranged tangential to the light-exit wall, a second reflective surface, coupled to the first reflective surface at a side of the first reflective surface that faces away from the first imaginary plane, the second reflective surface being defined in the second imaginary plane from the starting point that extends away from the light source.

The effect of the reflector according to the invention is that substantially all light emitted from the linear light source away from the light-exit window and reflected back to the light-exit window is distributed across the light-exit window. The shape of the first reflective surface is such that the shape at a point of the reflective surface is determined by the reflector tangent at the point that is substantially perpendicular to the source tangent, which is arranged tangential to the linear light source and intersects the point. Due to the shape of the first reflective surface, substantially all light emitted by the linear light source away from the light-exit window is reflected from the first reflective surface in the direction of the light-exit window while the shape of the first reflective surface avoids that the reflected light impinges on the linear light source. In the known backlight illumination system part of the light reflected from the reflector back toward the light-exit window impinges on the light source and is either scattered throughout the illumination system or (re- )absorbed in the light source. In the reflector according to the invention, the shape of the first reflective surface prevents that light reflected from the reflector impinges on the linear light source and is scattered or absorbed. Due to this arrangement the efficiency of the reflector according to the invention is increased with respect to a known backlight illumination system, resulting in reduced energy consumption and reduced cost of the backlight illumination system as lewer linear light sources may be applied.

The inventor has realized that the intensity of light emitted by the linear light source, which directly impinges on the light-exit window, is reduced when the distance to the linear light source increases. The decreasing contribution of light intensity directly emitted from the source must be compensated. The shape of the first reflective surface enables a gradual increase of the contribution of the reflected light to the overall light intensity at the light-exit window when the distance to the linear light source increases. Due to this gradual increase of the contribution of the reflected light, the light intensity distribution across the light-exit window is very uniform. In addition, the shape of the first reflective surface also reflects light towards an area of the light-exit window, which is located immediately opposite the linear light source, substantially up to the first imaginary plane. Because the gradual increase of the contribution of the reflected light already starts substantially at the first imaginary plane opposite the linear light source, a very uniform light intensity distribution is created across the whole light-exit window. In known illumination systems a distance between the linear light source and the light-exit window is increased to reduce intensity variations at the light-exit window directly opposite the linear light source. Due to the shape of the first reflective surface, this distance can be reduced in the backlight illumination system according to the invention, reducing a thickness of the overall backlight illumination system. Another benefit of the specific shape of the reflector according to the invention is that the backlight illumination system is less sensitive to manufacturing tolerances. In the known illumination systems the reflector consists of several reflective surfaces, each creating a reflective image of the light source. Each one of these reflective images (together with the light of the light source) must be overlapped to create a uniform light intensity distribution across the light-exit window. However, small manufacturing tolerances, such as a misalignment of the light source with respect to the reflector, would almost immediately be visible in the light intensity distribution at the light-exit window, because such a misalignment would influence the contribution to the light intensity uniformity of the light source and each one of the reflected sources. In the backlight illumination system according to the invention the linear light source and the plurality of reflected images of the linear light source reflecting from the first reflective surface can substantially be considered to be one single light source. Substantially no transition is visible at the light-exit window between the linear light source and each of the plurality of reflected images of the linear light source reflecting from the first reflective surface. Due to this substantially single light source the backlight illumination system according to the invention is less sensitive to manufacturing tolerances. Misalignment, for example, between the linear light source and the reflector according to the invention would result in a gradual intensity variation in a substantially single source, rather than a misalignment of a contribution to the light intensity of the linear light source and of the reflected images of the linear light source, as seen in the known illumination systems.

In an embodiment of the backlight illumination system, the curve is extended from the starting point in the direction of the side of the linear light source facing away from the light-exit window to intersect the first imaginary plane. A benefit of this embodiment is that also light emitted by the linear light source substantially perpendicular to the light-exit window away from the light-exit window, is reflected by the first reflective surface while the reflected light is prevented from impinging on the linear light source. This embodiment provides the highest possible efficiency of the backlight illumination system according to the invention. In an embodiment of the backlight illumination system, the reflective region comprises a third reflective surface which is defined in the second imaginary plane as a substantially straight line intersecting and substantially perpendicular to the first imaginary plane at the side of the linear light source facing away from the light emitting surface. A thickness of the backlight illumination system is defined by a largest distance between the reflective surface of the reflector and the light-exit window. A benefit of this embodiment is that the thickness of the backlight illumination system can be reduced. In the previous embodiment, the first reflective surface intersects the first imaginary plane. To still comply with the defined shape of the first reflective surface, the first reflective surface from the intersection with the first imaginary plane extends away from the linear light source, increasing the thickness of the backlight illumination system. Because the third reflective surface is arranged between the first reflective surface and the first imaginary plane, and because the third reflective surface can be placed very close to the linear light source, the thickness of the backlight illumination system can be reduced. In an embodiment of the backlight illumination system, the third reflective surface is coupled to the first reflective surface via a stopping point of the curve intersecting a stopping tangent which is arranged tangential to the light-exit wall and is arranged substantially parallel to the first imaginary plane. A benefit of this embodiment is that the thickness of the backlight illumination system can be minimized while still a relatively good efficiency is maintained.

In an embodiment of the backlight illumination system, the second reflective surface extends away from the linear light source in a substantial straight line perpendicular to the starting tangent. A benefit of this embodiment is that the second reflective surface can be easily manufactured, which reduces the manufacturing costs of the backlight illumination system.

BRIEF DESCRIPTION OF THE DRAWINGS:

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.

In the drawings:

Figl shows a planar view of the backlight illumination system according to the invention,

Fig. 2 shows a cross-sectional view of the backlight illumination system according to the invention,

Fig. 3 shows a graph indicating the light intensity at the light-exit window from the first imaginary plane of a first linear light source to the first imaginary plane of a second linear light source,

Fig. 4 shows a cross-sectional view of an alternative embodiment of the backlight illumination system according to the invention, and

Fig. 5 shows a display device according to the invention.

The figures are purely diagrammatic and not drawn to scale. Particularly for clarity, some dimensions are exaggerated strongly. Similar components in the figures are denoted by the same reference numerals as much as possible.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:

Fig.l shows a planar view of the backlight illumination system 10 according to the invention. The backlight illumination system 10 comprises a plurality of linear light sources 20 arranged substantially in parallel with each other. In the planar view of Fig. 1 only a single linear light source 20 is shown for clarity reasons. The plurality of linear light sources are arranged substantially parallel to a light-exit window 30 of the backlight illumination system 10 and comprise a light-exit wall 24 arranged around a longitudinal axis 22. The backlight illumination system 10 further comprises the light-exit window 30 arranged between the plurality of light sources and the display device 150 (see Fig. 5) and a reflector 40 arranged at a side of the linear light source 20 facing away from the light-exit window 30.

The reflector 40 comprises a reflective region for each of the linear light sources 20. The respective reflective regions are formed in symmetry with respect to each first imaginary plane 50 of the linear light sources 20 and extend substantially parallel to the linear light sources 20. The first imaginary plane 50 of the linear light source 20 comprises the longitudinal axis 22 and is arranged substantially perpendicular to the light-exit window 30. Each reflective region comprises a first reflective surface 70 and a second reflective surface 80. The first reflective surface 70 is concavely shaped with respect to the linear light source 20 and is defined by a curve 61 in a second imaginary plane 60. The second imaginary plane 60 is arranged perpendicular to the longitudinal axis 22 of the linear light source 20. The curve 61 extends from the starting point 63 in a direction of a side of the linear light source 20 facing away from the light-exit window 30. Each particular point of the curve 61 is defined by a reflector tangent 62 at the particular point that is arranged substantially perpendicular to a source tangent 64 intersecting the particular point. The reflector tangent 62 is arranged tangential to the curve 61. The source tangent 64 is arranged tangential to the light-exit wall 24 of the linear light source 20. The starting point 63 of the curve 61 intersects a starting tangent 66 which is arranged tangential to the light-exit wall 24 of the linear light source 20 and which intersects an intersection 68 between the first imaginary plane 50 and the light-exit window 30. The curve 61 extends from the starting point 63 in the direction of the side of the linear light source 20 facing away from the light-exit window 30 to intersect the first imaginary plane 50.

Fig. 2 shows a cross-sectional view of the backlight illumination system 10 along the second imaginary plane 60 according to the invention. Again a single linear light source 20 of the plurality of linear light sources 20 is drawn that comprises the light-exit wall 24 arranged around the longitudinal axis 22. The backlight illumination system 10 comprises the light-exit window 30 and the reflector 40, which is constituted by the first reflective surface 70 and the second reflective surface 80. The shape of the first reflective surface 70 is defined by the curve 61 as indicated in Fig. 1. Fig. 2 also shows the reflector tangent 62, the source tangent 64, the starting tangent 66 with the starting point 63, and the intersection 68 between the first imaginary plane 50 and the light-exit window 30. Fig. 2 additionally shows a first reflective image 26 of the linear light source 20 and a second reflective image 28 of the linear light source 20. The first reflective image 26 represents a reflection of the linear light source

20 due to the point on the first reflective surface 70 which intersects the first imaginary plane 50. The second reflective image 28 represents a reflection of the linear light source 20 due to the starting point 63 of the first reflective surface 70 (and due to the second reflective surface 80). Due to the shape of the first reflective surface 70 a continuous range of reflective surfaces are present between the first reflective image 26 and the second reflective image 28. If the reflector 40 would not be present in the backlight illumination system 10, an intensity of light at the light-exit window 30 would gradually diminish when moving along the light- exit window 30 from the intersection 68 away from the first imaginary plane 50. Due to the defined concave shape of the first reflective surface 70, a contribution of reflected light from the first reflective surface 70 which is added to the intensity of light at the light-exit window gradually increases when moving along the light-exit window 30 from the intersection 68 away from the first imaginary plane 50 (see also Fig. 3). The combination of light emitted by the linear light source 20 towards the light-exit surface 30 together with the light emitted by the linear light source 20 away from the light-exit window 30 and reflecting from the first reflective surface 70 back to the light-exit window 30 results in a uniform distribution of the light intensity across the light-exit window 30.

A benefit of the first reflective surface 70 is that the defined concave shape prevents substantially all light reflected from the first reflective surface 70 to impinge on the linear light source 20. In the known backlight illumination systems, part of the light reflected from the reflector back towards the light-exit window impinges on the light source and is either scattered throughout the system or (re-)absorbed in the light source. In the reflector 40 according to the invention the shape of the first reflective surface 70 prevents that light reflected from the reflector 40 impinges on the linear light source 20 and is scattered or absorbed. Due to this arrangement the efficiency of the reflector 40 is increased compared to known backlight illumination system.

A further benefit is that the shape of the first reflective surface 70 enables a gradual increase of the contribution of the reflected light to the overall light intensity at the light-exit window 30 when moving from the intersection 68 away from the first imaginary plane 50. Due to this gradual increase of the contribution of the reflected light, the light intensity distribution across the light-exit window 30 is very uniform. In addition, the concave shape of the first reflective surface 70 also reflects light towards an area of the light- exit window 30 which is located immediately opposite the linear light source 70, substantially up to the intersection 68 between the first imaginary plane 50 and the light-exit window 30. Because the gradual increase of the contribution of the reflected light already starts substantially at the intersection 68 opposite the linear light source, a very uniform light intensity distribution is created across the whole light-exit window 30.

A further benefit of the first reflective surface 70 is that the linear light source 20 and the plurality of reflected images 26, 28 substantially can be considered as a single light source. No transition is visible from the light-exit window towards the reflector from one light source or reflected light source to another light source or reflected light source. This substantially single light source is less sensitive to manufacturing tolerances of the backlight illumination system 10 according to the invention, in which, for example, the linear light source 20 is misaligned to the reflector 40. Fig. 3 shows a graph 100 indicating the light intensity I at the light-exit window 30 from a first intersection 68a of the first imaginary plane 50a of a first linear light source 20a to a second intersection 68b of the first imaginary plane 50b of a second linear light source 20b. The vertical axis 101 of the graph 100 represents a light intensity I at the light-exit window 30 of the backlight illumination system 10 according to the invention. The horizontal axis 103 of the graph 100 represents a displacement from the first intersection 68a to the second intersection 68b. A distance between the first imaginary plane 50a and the second imaginary plane 50b is indicated by d. A first line 102 indicates the intensity I of light emitted by the first linear light source 20a and the second linear light source 20b towards the light-exit window 30. A second line 104 and a third line 106 indicate the intensity I of light reflected from the reflector 40 arranged at the first light source 20a towards the light-exit window 30 and at the second light source 20b towards the light-exit window 30, respectively. A fourth line 108 indicates an overall intensity of light at the light-exit window 30, substantially being a sum of the first line 102 and the second line 104 and the third line 106. At the first intersection 68a and at the second intersection 68b the intensity I of the light at the light-exit window 30 substantially only consists of light emitted by the first linear light source 20a, and emitted by the second linear light source 20b, respectively. When moving from the first intersection 68a to the second intersection 68b, a contribution to the light intensity at the light-exit window 30 of both the light reflected from the first reflective surface 70a and the second reflective surface 80a of the first linear light source 20a (indicated by the second line 104), and a contribution of the light reflected from the first reflective surface 70b and the second reflective surface 80b of the second linear light source 20b (indicated by the third line 106) are added together. Due to the added contribution of the reflector 40 the overall intensity across the light-exit window 30 (indicated by the fourth line 108) is substantially uniform.

Fig. 4 shows a cross-sectional view of an alternative embodiment of the backlight illumination system 110 according to the invention. The backlight illumination system 110 shown in Fig. 4 also comprises a plurality of linear light sources 20 having a light-exit wall 24 arranged around the longitudinal axis 22. The linear light sources 20 are arranged substantially parallel to each other between the reflector 42 and the light-exit window 30 of the backlight illumination system 110. The reflector 42 comprises the first reflective surface 70 and the second reflective surface 80. The first reflective surface 70 is shaped as defined in Fig. 1. Fig. 4 shows the reflector tangent 62, the source tangent 64, the starting tangent 66 and the starting point 63. The reflector 42 of Fig. 4 also comprises a third reflective surface 90. The third reflective surface 90 is arranged substantially parallel to the light-exit window 30 and intersects substantially parallel to the first imaginary plane 50. The first reflective surface 70 is coupled to the third reflective surface 90 via a stopping point 92. The stopping point 92 is defined by a stopping tangent 94 arranged tangential to the light-exit wall 24 of the linear light source 20 and arranged substantially parallel to the first imaginary plane 50. The reflector tangent at the stopping point 92 (not shown) substantially overlaps the third reflective surface 90. A benefit of the use of the third reflective surface 90 in the reflector 42 is that the thickness of the backlight illumination system 110 can be reduced while still a relatively good efficiency is maintained. In the embodiment of the backlight illumination system 10 as shown in Figs. 1, 2 and 3, the first reflective surface 70 intersects the first imaginary plane 50. To be able to comply with the definition of the curve 61, which defines the shape of the first reflective surface 70, the first reflective surface 70 from the intersection with the first imaginary plane 50 extends away from the linear light source 20, increasing the thickness t of the backlight illumination system 10. The third reflective surface 90 can be located very close to the linear light source 20 and as such reduce the thickness t of the backlight illumination system 110 according to the invention.

Fig. 5 shows a display device 150 which comprises a backlight illumination system 10 according to the invention. The display device 150, for example, can be a non- emissive display, such as a liquid crystal display device, also referred to as LCD panel, which, for example, is used in (portable) computers, (cordless) telephones or remote-control units. The display device 150 may also, for example, be used as a digital projector or so- called beamer for projecting images or displaying a television program, a film, a video program or a DVD, or the like. In addition, the display device 150 may, for example, be used for general lighting purposes, such as for large-area direct-view light emitting panels such as applied, for instance, in signage, contour lighting, and billboards.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. A backlight illumination system (10, 110) for illuminating a display device

(150), the backlight illumination system (10, 110) comprising: a plurality of linear light sources (20) arranged substantially parallel to each other, each light source (20) having a longitudinal axis (22) and a light-exit wall (24) arranged around the longitudinal axis (22), a light-exit window (30) arranged between the plurality of light sources (20) and the display device (150) and arranged substantially parallel to the plurality of light sources (20) for emitting light towards the display device (100), and a reflector (40, 42) arranged at a side of the light sources (20) facing away from the light-exit window (30) for reflecting light emitted by the linear light source (20) towards the light-exit window (30), the reflector (40, 42) comprising a reflective region for each of the light sources (20), the respective reflective regions being formed in symmetry with respect to a first imaginary plane (50) through the longitudinal axis (22) of each of the light sources (20), the first imaginary plane (50) being arranged substantially perpendicular to the light-exit window (30), each reflective region extending substantially parallel to the light sources (20), each reflective region comprising: a first reflective surface (70) being concavely shaped with respect to the light source (20) defined by a curve (61) in a second imaginary plane (60) that is arranged perpendicular to the longitudinal axis (22), the curve (61) starting at a starting point (63) and extending from the starting point (63) in a direction of a side of the light source (20) facing away from the light-exit window (30), each point of the curve (61) being defined by a reflector tangent (62) that is arranged substantially perpendicular to a source tangent (64), the reflector tangent (62) being arranged tangential to the curve (61) at each respective point, the source tangent (64) intersecting the respective point and being arranged tangential to the light-exit wall (24), the starting point (63) being located on a starting tangent (66) intersecting an intersection (68) between the first imaginary plane (50) and the light-exit window (30) and being arranged tangential to the light-exit wall (24), a second reflective surface (80), coupled to the first reflective surface (70) at a side of the first reflective surface (70) that faces away from the first imaginary plane (50), the second reflective surface (80) being defined in the second imaginary plane (60) from the starting point (63) that extends away from the light source (20).

2. A backlight illumination system (10) as claimed in claim 1, wherein the curve

(61) is extended from the starting point (63) in the direction of the side of the light source (20) that faces away from the light-exit window (30) to intersect the first imaginary plane (50).

3. A backlight illumination system (110) as claimed in claim 1, wherein the reflective region comprises a third reflective surface (90) being defined in the second imaginary plane (60) as a substantially straight line intersecting and substantially perpendicular to the first imaginary plane (50) at the side of the light source (20) that faces away from the light emitting surface (30).

4. A backlight illumination system (110) as claimed in claim 3, wherein the third reflective surface (90) is coupled to the first reflective surface (70) via a stopping point (92) of the curve (61) intersecting a stopping tangent (94) that is arranged tangential to the light- exit wall (24) and is arranged substantially parallel to the first imaginary plane (50).

5. A backlight illumination system (10, 110) as claimed in any one of the previous claims, wherein the second reflective surface (80) extends away from the light source (20) in a substantially straight line perpendicular to the starting tangent (66, 76).

6. A display device (150) comprising the backlight illumination system (10, 110) as claimed in claim 1.