FIELD OF THE INVENTION

The present invention relates to the field of lighting, and in particular to the field of lighting for a desk or table.

BACKGROUND OF THE INVENTION

Whilst the increasing use of light emitting diodes (LEDs) increases a flexibility in lighting design, it also brings pixilation. This is commonly seen as an undesired or disturbing side-effect, and brings discomfort to a user. Light guide plates are becoming increasingly used to help distribute light emitted by light emitting diodes, to effectively soften and/or de-pixelate emitted light.

One use-case scenario for a light is a desk lamp. A challenge of desk lamps is that they are necessarily compact, which provides only limited space for the light emitting elements. There is therefore a difficulty in providing optical designs that have a wide and uniform illumination of a desk.

There is therefore a desire to provide a solution for desk lamps that resolves at least some of these problems or difficulties.

SUMMARY OF THE INVENTION

The invention is defined by the claims.

According to examples in accordance with an aspect of the invention, there is provided a light guide plate arrangement for a desk lamp.

The light guide plate arrangement comprises: a light guide plate for transmitting light, the light guide plate comprising: a light transmission window, configured to couple light transmitted by a light source into the light guide plate; and a light exit window configured to couple light out of the light guide plate, the light exit window making an angle of between 80° and 100° with respect to the light transmission window.

The light guide plate arrangement also comprises a first reflective surface positioned on the light guide plate and opposite the light transmission window for reflecting light incident upon the first reflective surface, wherein the light exit window is positioned between the light transmission window and the first reflective surface; a plurality of asymmetric light extraction features for directing light in the light guide plate towards the light exit window, wherein, for each asymmetric light extraction feature: in a first plane, being a plane parallel to the light exit window, the curvature of a first side of the asymmetric light extraction feature is greater than the curvature of a second side of the symmetric light extraction feature, wherein a longitudinal axis of the asymmetric light extraction feature makes a non-zero and non-perpendicular angle with respect to the light transmission window; and in a first plane, being a plane parallel to the light exit window, the curvature of a first side of the asymmetric light extraction feature is less than the curvature of a second side of the symmetric light extraction feature, wherein: the first side lies on one side of a second plane, being a plane perpendicular to the light exit window and passing through the longitudinal axis of the asymmetric light extraction feature; the second side of the asymmetric light extraction feature lies on the other side of the second plane; and the first side is more proximate to the light transmission window than the second side.

The present disclosure thereby proposes an approach in which the asymmetric light extraction features extend towards the light transmission window (and therefore light source) and away from the first reflective surface. This increases the amount of light that is guided, by the light guide plate, in a forward direction with respect to a direction in which light is transmitted into the light guide plate from the light source. This aids to improve the uniformity and spread of light distributed by the light guide plate.

The present disclosure also proposes to angle each asymmetric light extraction feature with respect to the light transmission window the light guide, and therefore the light source. This approach increases a sideways spread of the desk lamp.

Each asymmetric light extraction feature may be configured such that, in a second plane, being a plane perpendicular to the light exit window and perpendicular to the light transmission window, the curvature of the first side of the asymmetric light extraction feature is less than the curvature of the second side of the asymmetric light extraction feature.

Thus, in the second plane, the average gradient of the first side may be less than the average gradient of the second side.

This approach further enhances the effect of increasing the amount of light that is guided, by the light guide plate, in a forward direction with respect to a direction in which light is transmitted into the light guide plate from the light source.

Preferably, for each asymmetric light extraction feature, the longitudinal axis makes an angle of between 10° and 50° with respect to the light transmission window. The angle would modify or affect the sideward light direction. In some embodiments, the plurality of asymmetric light extraction features comprises at least 20 asymmetric light extraction features. The greater the number of features, the greater the effect provided by the plurality of asymmetric light extraction features. The at least 20 asymmetric light extraction features preferably comprises at least 50 asymmetric light extraction features, e.g., at least 100 asymmetric light extraction features.

The plurality of asymmetric light extraction features may be arranged in a pattern of two or more interwoven or overlapping columns. This approach increases the density of the asymmetric light extraction features, and therefore the effect provided by the asymmetric light extraction features.

Each of the plurality of asymmetric light extraction features may be formed from a hole or indentation in the light guide plate. This provides a mechanism for providing asymmetric light extraction features that is simple to manufacture, e.g., by modifying or etching existing molds for light guide plates.

As an alternative example, each of the plurality of asymmetric light extraction features may be formed from a different material to the remainder of the light guide plate, i.e., a material having a different refractive index.

In some examples, each of the plurality of asymmetric light extraction features is formed at a surface of the light guide plate opposite to the light exit window.

Preferably, each of the plurality of asymmetric light extraction features has a surface roughness, Ra, of between 0.1pm and 20pm. This increases the amount of light scattered by the asymmetric light extraction features, and therefore the uniformity of light distributed by the light guide plate.

The light exit window may make an angle of between 85° and 95° with respect to the light transmission window. In particular, the light exit window may be perpendicular to the light transmission window.

There is also proposed a lighting arrangement comprising: any herein described light guide plate arrangement; and the light source configured to transmit light towards the light transmission window. The optical axis of the transmitted light, e.g., the central axis, may be perpendicular to the light transmission window, e.g. be normal to the light transmission window.

There is also proposed a desk lamp comprising: a first lighting arrangement, being a herein described lighting arrangement; and a support for mounting the first lighting arrangement. The desk lamp may further comprise a second lighting arrangement, being another lighting arrangement as herein described. The support may be accordingly further configured to mount the second lighting arrangement.

Preferably, the plurality of asymmetric light extraction features of the first lighting arrangement is a mirrored version of the plurality of asymmetric light extraction features of the second lighting arrangement. This means that the sideway spread of light by the angled asymmetric light extraction features of the first and second lighting arrangements will be in opposite directions, increases the spread of the light provided by the desk lamp and improving a uniformity of the light provided by the desk lamp (as the sideways spreads will not overlap one another or have a reduced amount of overlap).

The support may be configured, when positioned on a flat surface, to permit the first lighting arrangement and the second lighting arrangement (if present) to be positioned at a distance greater than 30cm from the flat surface.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment s) described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

Figure 1 provides an exploded view of a lighting arrangement using a 3D perspective;

Figure 2 provides an assembled view of the lighting arrangement;

Figure 3 provides a cross-sectional view of the lighting arrangement in an X-Y plane;

Figure 4 illustrates an asymmetric light extraction feature in an X’-Y’ plane;

Figure 5 provides a cross-sectional view of the lighting arrangement in a Y-Z plane;

Figure 6 illustrates an asymmetric light extraction feature in a Y’-Z plane;

Figure 7 illustrates the propagation of a first light ray through a lighting arrangement;

Figure 8 illustrates the propagation of a second light ray through a lighting arrangement; Figure 9 illustrates a pattern for a plurality of asymmetric light extraction features;

Figure 10 illustrates a desk lamp;

Figure 11 illustrates a mirror symmetry for asymmetric light extraction features of two different lighting arrangements; and

Figure 12 provides an exploded view of a lighting arrangement.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention will be described with reference to the Figures.

It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

The invention provides a lighting arrangement with a light guide plate having asymmetric light extraction features. The asymmetric light extraction features bulge or extend towards a light transmission/entrance window/surface of the light guide plate, and are angled with respect to the light transmission window.

Embodiments are based on the realization that asymmetric light extraction features, i.e., light extraction features having an off-center optical axis, can aid in the control light emitted from a light guide plate of a desk lamp. In particular, the uniformity and spread of the light emitted by the light guide plate can be increased.

Proposed approaches can be used in any environment in which a desk lamp is to be used, for instance, offices, schools and/or home desk set-ups. Other suitable use-case scenarios will be readily apparent to the skilled person.

Figures 1 and 2 provide a 3D projection illustrating a lighting arrangement 50. Figure 1 provides an exploded view and Figure 2 provides an assembled view.

The lighting arrangement 50 comprises a light guide plate arrangement 100, itself an embodiment of the invention, and a light source 190. Figure 1 identifies three axes for the lighting arrangement 50 and/or the light guide plate arrangement 100. These axes include an X-axis that spans a width of the light guide plate arrangement, a Y-axis that spans a length of the light guide plate arrangement, and a Z-axis that spans a height or depth of the light guide plate arrangement.

The light guide plate arrangement 100 comprises a light guide plate 105, a first reflective surface 120, a plurality of asymmetric light extraction features 150, an (optional) second reflective surface 170 and (optional) side reflective surfaces 181, 182.

For illustrative clarity, the illustration of the second reflective surface 170 and one of the side reflective surfaces 181 has been omitted in Figure 2.

The light guide plate 105 is configured for transmitting light, e.g., is formed from a transparent and/or translucent material. The light guide plate comprises a transmission window 110 and a light exit window 130. The light transmission window 110 is configured to couple light transmitted by the light source (e.g., positioned to emit light towards the light transmission window 110) into the light guide plate. The light exit window 130 is configured to couple light out of the light exit window 130. Light is generally transmitted into the light guide plate 105 along the y-axis.

The light exit window 130 makes an angle of between 80° and 100° with respect to the light transmission window 110. In this way, the light exit window may be substantially perpendicular or perpendicular to the light transmission window. For instance, the light exit window may make an angle of between 85° and 95° with respect to the light transmission window.

In Figures 1 and 2, the light exit window 130 is located on an underside of the illustrated lighting arrangement.

Thus, the light exit window lies in the X-Y plane. The light transmission window 110 is located in the X-Z plane, and is therefore perpendicular to the light exit window 130. The directions of the axes X, Y, Z may be defined by the planes in which the light transmission window and light exit window lies. In particular, the light transmission window lies in an X-Z plane and the light exit window lies in an X-Y plane.

In this way, the lighting arrangement 50 has a side-lit design, as the light is redirected from the light transmission window 110 by the light guide plate to exit at a nonzero angle to the light transmission window 110 (via the light exit window 130).

Approaches for forming a light transmission window, also known as a light entrance window, and/or a light exit window are well known in the art, and may comprise appropriately texturing or shaping the window(s) to facilitate the coupling of light into/out of the light guide plate.

The first reflective surface 120 is positioned on the light guide plate 105 opposite the light transmission window 110. The first reflective surface is configured to reflect light incident thereupon. Approaches for forming a first reflective surface 120 include depositing a reflective material upon a surface of the light guide plate 105 and/or coupling a reflective layer/slice of material to a surface of the light guide plate 105.

The light exit window 130 is located between the light transmission window 110 and the first reflective surface 120. In this way, the light exit window also makes a nonzero angle with respect to the first reflective surface 120. For instance, the light exit window 130 may make an angle of between 80° and 100° with respect to the first reflective surface 120, e.g., be substantially perpendicular to the first reflective surface 120.

The plurality of asymmetric light extraction features are configured to aid in the directing of light towards the light exit window.

Each asymmetric light extraction feature may be formed as a feature of/in the light guide plate 105.

As illustrated, each of the plurality of asymmetric light extraction features may be formed from a hole or indentation in the light guide plate. This approach provides a light guide plate arrangement that is easy to manufacture, e.g., as the light extraction features can be integrated into the light guide plate through simple modification of a mold or form(er) for the light guide plate.

As another example, each asymmetric light extraction feature may be formed from a protrusion or bulge out of the light guide plate. This approach is similarly easy to manufacture, but reduces the compactness of the light guide plate.

In this way, each asymmetric light extraction feature may be formed at a surface 160 of the light guide plate 105 opposite to the light exit window. Similarly, the light guide plate may comprise a plurality of 3D textures (being holes and/or protrusions) that are located on a surface opposite to the light exit window.

As yet another example, each asymmetric light extraction feature may be formed of a separate material to the remainder of the light guide plate. This can be performed, for instance, by forming holes/indentations in the light guide plate and filling said holes with material or by depositing protrusions of a different material on the light guide plate. As an example of asymmetric light extraction features not formed as a feature of/in the light guide plate, each of the plurality of asymmetric light extraction features may be formed in a separate layer which is coupled to the light guide plate, e.g., on a surface opposite to the light exit window.

If present, the second reflective surface 170 and the side reflective surface(s) 181, 182 are configured to reflect light back into the light guide plate, i.e., contain light within the light guide plate. These reflective surfaces may be formed in the same way or a similar way to the first reflective surface 120. The second reflective surface 170 is positioned opposite the light exit window, e.g., on an upper side 135 of the light guide plate. The side reflective surfaces 181, 182 are located on respective side surfaces 136, 137 of the light guide plate.

The light source 190 is configured to transmit light towards the light transmission window 110. The light source 190 may comprise one or more light emitting diodes for generating the light that is transmitted towards the light transmission window 110. Although not illustrated, the light source 190 may be held in place by a printed circuit board.

One or both of the side reflective surfaces 181, 182 may be replaced with an additional light source, e.g., an additional set of one or more light emitting diodes. These light sources may be configured to emit light into a second light transmission window of the light guide plate. The second light transmission window may be perpendicular to the light transmission window. This approach would enhance the amount of light in the light guide plate.

Preferably, the plurality of asymmetric light extraction features comprises at least 20 asymmetric light extraction features, e.g., no less than 100 asymmetric light extraction features, e.g., no less than 500 asymmetric light extraction features.

Figure 3 provides a view of the light guide plate arrangement 100 in the X-Y plane, which can be labelled a “first plane”. The size of the asymmetric light extraction features has been exaggerated, for the purposes of illustrative clarity and explanation.

Each asymmetric light extraction feature is configured such that, in the first plane X-Y, the curvature of a first side 151 of the asymmetric light extraction feature is less than the curvature of a second side 152 of the symmetric light extraction feature. The first side is more proximate to the light transmission window 110 than the second side.

Thus, each asymmetric light extraction feature bulges towards the light transmission window. The average distance between the edge of the first side and the center of the asymmetric light extraction feature is therefore greater than the average distance between the edge of the second side and the center of the asymmetric light extraction feature.

This approach means that the optical axis of the asymmetric light extraction feature is off-center, at least with respect to the first plane X-Y. The shape of each asymmetric light extraction feature causes more light to be distributed towards the opposite side of the light guide plate to the light transmission window, i.e. increases the distribution of light to locations more distant from the light source.

Figure 4 provides an enlarged view of the asymmetric light extraction feature, with respect to a plane X’-Y’, which lies in a same overall plane as the plane X-Y, but with an axial rotation (e.g., about the Z-axis, which leads into/out of the sheet).

Figure 4 illustrates how the asymmetric light extraction feature may be shaped like a skewed oval, in which one side 151 of the feature bulges outwardly (in the X-Y plane) to a greater extent than the other side 152 of the feature.

Turning back to Figure 3, each asymmetric light extraction feature is also configured such that the longitudinal axis 159 of the asymmetric light extraction feature makes a non-zero and non-perpendicular angle with respect to the light transmission window.

The longitudinal axis 159 is the axis that passes through the widest or longest part of the asymmetric light extraction feature in the first plane, i.e., along the length of the asymmetric light extraction feature. The term longitudinal axis is well used and established in the art to refer to such an axis for objects or elements.

This approach increases the distribution of light sidewards or sideways with respect to the transmission of light by the light source, e.g., towards a direction in the third quadrant of X-Y plane.

Preferably, for each asymmetric light extraction feature, the longitudinal axis makes an angle of between 10° and 50° with respect to the light transmission window.

The first side 151 of the asymmetric light extraction feature lies on one side of the longitudinal axis. The second side 152 of the asymmetric light extraction feature lies on the other side of the longitudinal axis.

Put another way, the first side 151 of the asymmetric light extraction feature 150 lies on one side of a second plane, being a plane perpendicular to the light exit window and passing through the longitudinal axis 159 of the asymmetric light extraction feature 150. The second side 152 of the asymmetric light extraction feature 150 lies on the other side of the second plane. The average distance between the edge of the first side 151 and the longitudinal axis 159 is greater than the average distance between the edge of the second side 152 and the longitudinal axis 159.

Figure 5 provides a view of the light guide plate arrangement 100 in the Y-Z plane, which can be labelled a “second plane”. Only one asymmetric light extraction feature 150 is illustrated, the size of which has been exaggerated, for the purposes of illustrative clarity and explanation.

The asymmetric light extraction feature 150 is configured such that, in a second plane, being a plane perpendicular to the light exit window 130 and parallel to the light transmission window, the curvature of the first side 151 of the asymmetric light extraction feature 150 is less than the curvature of the second side 152 of the asymmetric light extraction feature 150.

Put another way, the (average) steepness of the first side 151 is less than the (average) steepness of the second side 152 in the Y-Z plane. This is illustrated by tangents Gl, G2, which represent the average steepness of both sides of the asymmetric light extraction feature.

In other words, the first side 151 may be (on average) less steep/inclined/sloped with respect to the light exit window than the second side 152.

Figure 6 provides an enlarged view of the asymmetric light extraction feature, with respect to a Y’-Z plane which lies in a same overall plane as the plane Y-Z, but with an axial rotation about the Z-axis.

Figure 6 illustrates how the asymmetric light extraction feature 150 may be shaped like a skewed hemi-circle, in which one side 151 of the feature has a lesser curvature than the other side 152 of the feature.

As previously explained, the first side 151 of the asymmetric light extraction feature 150 lies on one side of a second plane 510, being a plane perpendicular to the light exit window and passing through the longitudinal axis 159 of the asymmetric light extraction feature 150. The second side 152 of the asymmetric light extraction feature 150 lies on the other side of the second plane.

This approach means that the optical axis of the asymmetric light extraction feature 150 is off-center, at least with respect to the first plane Y’-Z’. The shape of the asymmetric light extraction feature 150 causes more light to be distributed towards the opposite side of the light guide plate to the light transmission window, i.e. increased the distribution of light to locations more distant from the light source. Figures 7 and 8 illustrate the effect of the shape of the asymmetric light extraction feature 150, particularly one in which the (average) steepness of the first side 151 is less than the (average) steepness of the second side 152 (in the Y-Z plane).

Figure 7 illustrates a scenario in which a first light ray 710 is emitted from the light source 190 through the light transmission window 110 at an angle of 0i with respect to the normal Ni to the light transmission window.

The angle 0i is such that when the first light ray 710 reaches the interface between the asymmetric light extraction feature and the remainder of the light guide plate, the angle of incidence is greater than the critical angle for the interface. Thus, the first light ray 710 is reflected towards the light exit window in a forward direction (i.e., in a direction having a positive component in the direction of a normal to the light transmission window reaching into the light guide plate).

Figure 8 illustrates a scenario in which a second light ray 810 is emitted from the light source 190 through the light transmission window 110 at an angle of 02 with respect to the normal to the light transmission window. The angle 02 has an equal absolute value to the angle 0i, but opposite direction.

The angle 02 is such that when the second light ray 810 the light exit window, it undergoes total internal reflection. The second light ray 810 is then reflected by the first reflective surface 120. The angle 02 between the normal N2 to first reflective surface and the second light ray (when it has been reflected by the first reflective surface) remains at the angle 02, due to the laws of reflection.

In principle, if the first 151 and second 152 sides of the asymmetric light extraction feature 150 had identical curvatures, the second light ray 810 would also undergo total internal reflection at the interface to the asymmetric light extraction feature and be reflected towards the light exit window 130. Thus, the second light ray 810 would be directed in a rearward direction with respect to the direction of light transmitted into the light guide plate 105.

However, because the curvature of the second side 152 is greater than the first side 151, the second light ray 810 is instead refracted into the asymmetric light extraction feature.

This approach thereby reduces the number of light rays that exit the light exit window in a rearward direction, i.e., in a direction having a negative component in the direction of a normal Ni to the light transmission window reaching into the light guide plate. Figure 9 illustrates a pattern 900 for a plurality of asymmetric light extraction features 150. The pattern is formed of two or more interwoven or overlapping columns 911, 912, 913 of asymmetric light extraction features 150. This approach increases the number of asymmetric light extraction features 150 that can be provided per unit area, thereby increasing the effectiveness of the light redirecting of the plurality of asymmetric light extraction features 150.

In any above described embodiment, each of the plurality of asymmetric light extraction features 150 may have a surface roughness, Ra, of between 0.1pm and 20pm, e.g., between 2pm and 20pm, e.g., between 5pm and 20pm. Ra is a well-known parameter of surface roughness, and indicates the average, or arithmetic average of profile height deviations from the mean line.

Increased surface roughness will increase the amount of light scattering or diffusion performed within the light guide plate arrangement 100, such that light emitted from the light guide plate arrangement 100 will have a more uniform light distribution.

One suitable method of preparing a surface having such a surface roughness is to etch or engrave the inner surface of an (injection) mold for the light guide plate and/or asymmetric light extraction features. The surface roughness will then be transferred to the asymmetric light extraction features during the molding process.

An alternative approach is to directly engrave or etch the asymmetric light extraction features themselves. This is less preferred due to the more resource-intensive manufacturing process.

Figure 10 illustrates a desk lamp 10 according to an embodiment.

The desk lamp 10 comprises a first lighting arrangement 50A, as previously described, and a support 1010 for mounting the first lighting arrangement. The desk lamp 10 further comprises a (optional) second lighting arrangement 50B, which the support 1010 is also configured to mount.

The desk lamp 10 therefore comprises a light system 1050 comprises the first lighting arrangement 50A and the second lighting arrangement 50B.

The support 1010 may be configured, when positioned on a flat surface 1090, to permit the first lighting arrangement and second lighting arrangement (if present) to be positioned at a distance d greater than 30cm from the flat surface 1090. Of course, the size of the distance may be adjustable, e.g., the support 1010 may be height adjustable.

Preferably, the support 1010 is configured to, when positioned on a flat surface 1090, prevent the distance d from being greater than Im In this way, the desk lamp can be specifically configured for use with desks.

Preferably, the plurality of asymmetric light extraction features of the second lighting arrangement 50B is a mirrored version of the plurality of asymmetric light extraction features of the first lighting arrangement 50A. This approach provides a more even distribution of light over the surface on which the desk lamp sits.

The line of reflective symmetry may, for instance, be a line parallel to the normal to the light transmitting window of the light guide plate of the first or second lighting arrangement.

Figure 11 illustrates this concept.

In particular, Figure 11 illustrates a first pattem/plurality 1101 of asymmetric light extraction features for a first lighting arrangement, and a second pattern/plurality 1102 of asymmetric light extraction features for a second lighting arrangement. For illustrative clarity, a respective light source 190 and light transmission window 110 for each pattern/plurality of asymmetric light extraction features is also illustrated.

Figure 11 demonstrates how the first pattern/plurality 1101 of asymmetric light extraction features of the first lighting arrangement may be a mirrored version of the second pattern/plurality 1102 of asymmetric light extraction features 150 of the second lighting arrangement. The line/plane of reflective symmetry (i.e., the virtual mirror) 1150 is a line/plane perpendicular to the light transmitted window 110, i.e., lies in the y-axis.

The first and second lighting arrangements are thereby effectively mirrors of one another, to distribute the light forward to both sides.

Figure 12 provide an exploded view of a lighting arrangement 50, illustrating further optional features of the lighting arrangement.

The lighting arrangement 50 comprises a light guide plate 105, a light source 190, an (optional) second reflective surface 170 and a lower 1110 and upper 1120 mounting element. The lower 1110 and upper 1120 mounting elements connect or co-operate with one another to mount and/or support the other elements of the lighting arrangement.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

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. If the term "adapted to" is used in the claims or description, it is noted the term "adapted to" is intended to be equivalent to the term "configured to". If the term "arrangement" is used in the claims or description, it is noted the term "arrangement" is intended to be equivalent to the term "system", and vice versa. Any reference signs in the claims should not be construed as limiting the scope.