GB2568864A - A waveguide and lighting device comprising the waveguide - Google Patents

A waveguide and lighting device comprising the waveguide Download PDF

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Publication number
GB2568864A
GB2568864A GB1716389.0A GB201716389A GB2568864A GB 2568864 A GB2568864 A GB 2568864A GB 201716389 A GB201716389 A GB 201716389A GB 2568864 A GB2568864 A GB 2568864A
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United Kingdom
Prior art keywords
waveguide
width
patterned reflector
reflector strip
strip
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GB1716389.0A
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GB201716389D0 (en
Inventor
Wilfred James Halton Luke
Kit Buchanan William
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Waveguide Lighting Ltd
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Waveguide Lighting Ltd
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Priority to GB1716389.0A priority Critical patent/GB2568864A/en
Publication of GB201716389D0 publication Critical patent/GB201716389D0/en
Publication of GB2568864A publication Critical patent/GB2568864A/en
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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
    • G02B6/0005—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being of the fibre type
    • G02B6/001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being of the fibre type the light being emitted along at least a portion of the lateral surface of the fibre
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V7/00—Reflectors for light sources
    • F21V7/0091—Reflectors for light sources using total internal reflection
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
    • G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
    • G02B6/0013—Means for improving the coupling-in of light from the light source into the light guide
    • G02B6/0015—Means for improving the coupling-in of light from the light source into the light guide provided on the surface of the light guide or in the bulk of it
    • G02B6/0018—Redirecting means on the surface of the light guide
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
    • G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
    • G02B6/0033—Means for improving the coupling-out of light from the light guide
    • G02B6/005—Means for improving the coupling-out of light from the light guide provided by one optical element, or plurality thereof, placed on the light output side of the light guide
    • G02B6/0055—Reflecting element, sheet or layer
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
    • G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
    • G02B6/0033—Means for improving the coupling-out of light from the light guide
    • G02B6/0058—Means for improving the coupling-out of light from the light guide varying in density, size, shape or depth along the light guide

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Planar Illumination Modules (AREA)

Abstract

A waveguide for lighting that comprises a transparent material 20a, preferably acrylic, which carries light, preferably from an LED, along its length by total internal reflection, and a patterned reflector strip 30a on the transparent material for reflecting light out of the waveguide. The patterned reflector strip has two areas, a first area of reflective material 61a, and a second area devoid of reflective material 62a, and where an average density (Ds) of the first areas 61a compared to the second areas 62a taken along the length of the patterned reflector strip, varies across a width (Ws) of the patterned reflector strip. The areas can form a repeating, alternating pattern, and the areas can be similar sizes. The first areas 61a may take up the full width of the reflector strip 30a, and can be symmetrical. The density at mid-way width (W0.5) can be the maximum or minimum.

Description

A WAVEGUIDE AND LIGHTING DEVICE COMPRISING THE WAVEGUIDE
DESCRIPTION
The present invention relates to a waveguide, in particular to a waveguide that can be used to emit light in a lighting device.
BACKGROUND OF THE INVENTION
In recent years, Light Emitting Diode (LED) technology has developed to the point where it can start to replace conventional incandescent and strip lighting. One of the problems in adapting LEDs to emulate known strip lighting is that LED’s are typically point light sources which do not emit light over large areas, like the phosphors in conventional strip lights can.
It is known to solve this problem by providing a length of transparent material that defines a waveguide. Then, light from an LED can be emitted into an end of the waveguide, and the light will travel along the waveguide by total internal reflection, in a similar manner to light inside of an optical cable. A reflective material can be formed on a surface of the waveguide to disrupt the total internal reflection and cause the light to be emitted from the waveguide. For example, a known waveguide of that type is described in GB 2,398,372, where a reflective strip is formed with a length extending along the length of the waveguide.
The wider the reflective strip, the more light is reflected from the strip, but the more quickly the light intensity reduces along the length of the waveguide. This is because the light has a higher likelihood of reflecting off the reflective strip and out the waveguide, and a lower likelihood of being totally internally reflected and carried further along the waveguide, compared to if a narrower reflective strip were used.
In many lighting applications, it is desirable to provide a wide angle of light emission from the waveguide. The wider the reflective strip, the wider the angle of light emission. However, making the strip wide suffers from the problem of reducing the distance that the light totally internally reflects along the waveguide, as outlined in the paragraph above.
The intensity of light emission is greatest in an angular direction that is perpendicular to the strip, and the intensity steadily drops off in angular directions away from perpendicular to the strip. An illustration of this is shown in Fig. 1, which shows a cross-sectional view through a waveguide 1. Light travels along the waveguide 1 by total internal reflection, and the waveguide 1 has a reflective strip 2 on its exterior surface. The reflective strip disrupts the total internal reflection, and causes light generally designated at 3 to be emitted from the waveguide. The intensity of the light 3 along the plane 4 is shown in the graph 5. The trace 6 shows that the light intensity is highest in a direction 7 perpendicular to the reflective strip 2, and steady reduces for directions away from direction 7.
It would also be desirable to provide control over how the intensity of light varies in different angular directions away from the waveguide, for example so that the intensity could be more uniform over the angles at which light is emitted, more concentred towards the angular direction that is perpendicular to the strip, or offset to give greatest intensity over one side of the direction that is perpendicular to the strip.
It is therefore an object of the invention to provide an improved waveguide.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, there is provided a waveguide comprising a transparent material which carries light along a length of the transparent material by total internal reflection, and a patterned reflector strip on the transparent material for reflecting light out of the waveguide. The patterned reflector strip has a length aligned with the length of the transparent material, and comprises first areas of reflective material and second areas which are devoid of reflective material. An average density of the first areas compared to the second areas taken along the length of the patterned reflector strip, varies across a width of the patterned reflector strip.
The transparent material carries light along the waveguide by total internal reflection, and may consist of a single block of transparent material. The light is transmitted through the transparent material, and internally reflects at the exterior surfaces of the transparent material. The light that reflects off the patterned reflector strip does not internally reflect when it reaches the exterior surface of the transparent material, but instead passes through the exterior surface and out of the waveguide.
Since the average density of the first areas varies across the width of the patterned reflector strip, the patterned reflector strip reflects different amounts of light at different locations along the width of the strip. Higher light intensities are emitted from the waveguide in directions where light is reflected from width portions of the patterned reflector strip that have a higher average density, and lower light intensities are emitted from the waveguide in directions where light is reflected from width portions of the patterned reflector strip that have a lower average density.
The average density along the width of the strip can be varied to produce almost endless variations in the angular distribution of intensities of light emitted from the waveguide. For the avoidance of any doubt, the angular distribution of intensities of light is measured over a plane transverse to the length of the waveguide.
The first areas and the second areas may alternate with one another along the length of the patterned reflector strip, for example to form a repetitive pattern along the length of the patterned reflector strip. In such a case, the average density for a point along the width of the strip may be calculated by defining a line extending through the point in the length direction of the strip, the line having a length corresponding to one period of the repetitive pattern, and dividing the total length(s) of the line in the first areas by the total length of the line. Clearly, all areas of the strip that are not first areas, must be second areas, and so the average density could equivalently be calculated by dividing the total length(s) of the line in the first areas by the total lengths of the line in the second areas, rather than by the total length of the line as a whole. Alternatively, the average density may be calculated along a line extending the whole length of the strip, rather than along one period of a repetitive pattern.
The width of the patterned reflector strip may be defined as the maximum extent of the first areas in a direction perpendicular to the length of the transparent material, and the length of the patterned reflector strip may be defined as the maximum extent of the first areas in a direction parallel to the length of the transparent material. Optionally, each first area may extend fully across the full width of the patterned reflector strip.
Each first area may extend further across the width of the patterned reflector strip than it extends along the length of the patterned reflector strip. This allows the first areas to vary the angular distribution of light intensities emitted from the waveguide, whilst minimising changes in the light intensity emitted in directions along the waveguide. Then the angular distribution of light intensity emitted from the waveguide can be fairly consistent along the length of the waveguide. The first areas may all be a same size as one another, and the second areas may all be same size as one another.
Each first area may comprise a perimeter having an arc shaped segment, to help provide smooth changes in the light intensities emitted from the waveguide. For example, each first area may comprise two of the arc shaped segments arranged symmetrically with one another. Each first area may be symmetrical about the width of the first area, so that any variation in emitted light intensity along the length of the waveguide is smooth. Each first area may be symmetrical about the length of the first area, so that the angular distribution of light intensities emitted from the waveguide is symmetrical about the central axis of the patterned reflector strip.
The average density may be at a maximum mid-way along the width of the patterned reflector strip, to provide a maximum intensity of light emission from the waveguide mid-way through the angular distribution of light intensities emitted from the waveguide, and concentrate the emitted light more towards mid-way through the angular distribution of light intensities compared to known waveguides having reflector strips that lack any patterning of reflective material. This is useful for applications requiring a concentrated beam (line) of light to be emitted from the waveguide. The average density may gradually and smoothly reduce away from mid-way along the width of the patterned reflector strip, to provide a smooth reduction in the angular distribution of light intensity away from mid-way through the angular distribution of light intensities.
Alternatively, the average density may be at a minimum mid-way along the width of the patterned reflector strip, to reduce the intensity of light emission from the waveguide mid-way through the angular distribution of light intensities emitted from the waveguide, and more uniformly spread the emitted light across the range of angles at which light is emitted from the waveguide, in comparison to waveguides having reflector strips that lack any patterning of reflective material. The average density may gradually and smoothly increase away from mid-way along the width of the patterned reflector strip, to provide a smooth (or zero) variation in the angular distribution of light intensity away from mid-way through the angular distribution of light intensities.
In another alternative, the average density may gradually and smoothly increase along a portion of the width of the patterned reflector strip, the portion having a middle region including mid-way along the width of the patterned reflector strip width. Then, the maximum average density is offset from mid-way along the width of the patterned reflector, and the angular distribution of light intensities emitted from the waveguide has a light intensity which steadily increases across the range of angles at which light is emitted. This is useful for applications where the light emitted at higher intensity is to light areas that are further away from the waveguide than areas which are lit by the light emitted at a lower intensity, so that the amount of light than actually reaches each of the areas is broadly the same. For example, this finds applications in signage where the waveguide may be mounted along the bottom of the sign.
The average density may gradually and smoothly reduce to zero over opposing end portions of the width of the patterned reflector strip, to provide a smooth reduction to substantially zero light emission at the maximum angular extents of light emission from the waveguide. Preferably, each end portion comprises no more than 20% of the width of the patterned reflector strip, more preferably no more than 15%, or no more than 10%.
The patterned reflector strip may be on or adjacent an exterior surface of the length of transparent material, and may for example be formed as a coating on the exterior surface. The coating may for example be a reflective white paint. The patterned reflector strip may extend along substantially a full length of the length of transparent material, so the waveguide emits light along substantially its full length.
The transparent material may for example be in the shape of a cylinder, although may alternatively have other cross-sectional shapes besides circular shapes, for example oval shapes. There are several types of materials that could be used as the transparent material, as will be apparent to those skilled in the art. For example, the transparent material could be an acrylic material. Preferably, the transparent material has a uniform cross section along its length, for example it may be formed as an extrusion of a plastics material.
The patterned reflective strip may be curved across its width, for example to follow the exterior surface of the transparent material. The curvature helps to spread the emitted light out over a range of angles.
In some embodiments, there may be a plurality of the patterned reflector strips arranged parallel to one another along the length of the transparent material, so that each patterned reflector strip causes reflection of light out of the waveguide at a different angles to the other patterned reflective strip(s). For example, the plurality of patterned reflector strips may be spaced apart from one another at regular intervals to emit light at regular angular intervals around the waveguide.
According to a second aspect of the invention, there is provided a lighting device comprising the waveguide of the first aspect, and a lamp mounted adjacent an end of the waveguide, the lamp for emitting light into the end of the waveguide. Preferably, the lamp is an LED lamp.
DETAILED DESCRIPTION
Embodiments of the invention will now be described by way of non-limiting example only and with reference to the accompanying drawings, in which:
Fig. 1 shows a schematic diagram of the angular distribution of light intensities from a known waveguide;
Fig. 2 shows a schematic cross-sectional diagram of a lighting device according to an embodiment of the invention;
Fig. 3 shows another schematic cross-sectional diagram of the lighting device of Fig. 2, taken along XS1 marked on Fig 1; and
Figs. 4a and 4b show schematic diagrams of two possible patterned reflective strips for use in the lighting device of Figs. 2 and 3;
Fig. 5 shows an angular distribution of light intensities from the lighting device of Figs. 2 and 3 when implementing the patterned reflective strip of Fig. 4b;
Figs. 6a to 6c show schematic diagrams of three further possible patterned reflective strips for use in the lighting device of Figs. 2 and 3;
Fig. 7 shows an angular distribution of light intensities from the lighting device of Figs. 2 and 3 when implementing the patterned reflective strip of Fig. 6a;
Figs. 8a and 8b show schematic diagrams of two further possible patterned reflective strips for use in the lighting device of Figs. 2 and 3;
Fig. 9 shows an angular distribution of light intensities from the lighting device of Figs. 2 and 3 when implementing the patterned reflective strip of Fig. 8b; and
Fig. 10 shows a schematic cross-sectional diagram of an alternate waveguide for use in the lighting device of Fig. 2.
The figures are not to scale, and same or similar reference signs denote same or similar features.
The schematic diagram of Fig. 2 shows a cross-section taken along the length of a lighting device. The lighting device comprises a waveguide 15, formed by a cylindrical body of transparent material 20. Two end caps 5 are mounted at opposite ends 22 and 24 of the cylindrical body of transparent material 20. Each end cap 5 has sides 12 extending outwardly from a main body 10, the sides forming a circular cup into which an end of the transparent material 20 can be inserted.
Each main body 10 comprises an LED light source, which emits light into the corresponding end of the cylindrical body of transparent material 20. Each LED light source comprises one or more LEDs, and a heatsink for dissipating excess heat. The main body 10 also comprises LED drivers for driving the LED(s), although the LED drivers could be located remotely from the main body 10 in alternate embodiments. A small gap 14 exists between the main body 10 and the cylindrical body of transparent material 20 to help prevent overheating of the cylindrical body of transparent material 20.
The main body 10 has a reflective surface 11 facing towards the corresponding end of the cylindrical body of transparent material 20, and apertures (not shown in Figs) are provided through the reflective surface to allow light to exit from the LED(s) in the main body and into the transparent material 20.
The cylindrical body of transparent material 20 has a patterned reflective strip 30 on the exterior surface of the cylindrical body of transparent material, parallel to a central axis along the length of the cylindrical body of transparent material. This can be seen in Fig. 3, which shows a cross-section through the cylindrical body of transparent material 20, taken along line XS1 marked on Fig. 2.
The cylindrical body of transparent material 20 has an exterior surface 26 which has a circular cross section, and reflective material is coated on the exterior surface to define the patterned reflective strip 30. In this particular embodiment, the coating is applied as a white reflective paint which is painted onto the exterior surface 26. The cylindrical body of transparent material 20 has the same cross section along its whole length, and may for example be formed as an extrusion or by moulding.
In use, the end caps 5 each emit LED light into a respective end of the cylindrical body of transparent material 20, and the cylindrical body of transparent material 20 transmits the light towards the middle 50 of the waveguide by total internal reflection. Light that travels all the way along the waveguide from one end cap 5 to the other end cap 5, is reflected back into the waveguide by the reflective surface 11.
As the light is internally reflected along the waveguide, some of the light reflects off the patterned reflective strip 30. This changes the direction of the light, and causes it to exit the waveguide through the exterior surface 26, rather than being totally internally reflected again.
The schematic diagrams of Figs. 4a and 4b show two alternative plan views of the waveguide 15 when looking from direction 40 marked on Figs 2 and 3. Specifically, Fig. 4a shows a first possible option with the transparent material 20 designated as 20a and the reflective strip 30 designated as 30a, and Fig. 4b shows a second possible option with the transparent material 20 designated as 20b and the reflective strip 30 designated as 30b.
The patterned reflective strip 30a on the transparent material 20a comprises first areas 61a which are areas filled with reflective material, and second areas 62a which are areas devoid of any reflective material. Similarly, the patterned reflective strip 30b on the transparent material 20b comprises first areas 61b which are areas filled with reflective material, and second areas 62b which are areas devoid of any reflective material. The first and second areas are arranged in a repetitive pattern that extends the full length of each patterned reflective strip 30a and 30b.
The first areas of each patterned reflective strip 30a and 30b are all the same size as one another, and are wider than they are long. They are also symmetrical about a central axis of the patterned reflective strip, the central axis aligned along the length of the patterned reflective strip, mid-way along the width of the patterned reflective strip. Each first area 61a, 61b is also symmetrical about its own length, which is aligned with the length of the patterned reflective strip, and about its own width, which is aligned with the width of the patterned reflective strip.
Beneath each of the transparent materials 20a and 20b are shown graphs with traces 100a and 100b illustrating the average density Ds of the first areas compared to the second areas along the widths Ws of the patterned reflective strips 30a and 30b. The trace 100a shows that the average density of first areas to second areas taken along the length of the strip begins at zero at width Wo, corresponding to the far left of the strip 30a as viewed in Fig. 4a, linearly ramps up to a maximum mid-way along the width of the strip at W0.5, and linearly ramps back down to zero at width Wi, corresponding to the far right of the strip 30a as viewed in Fig. 4a.
The trace 100b shows that the average density of first areas to second areas taken along the length of the strip begins at zero at width Wo, corresponding to the far left of the strip 30b as viewed in Fig. 4b, curves up in an S-curve to a maximum mid-way along the width of the strip at W0.5, and curves back down in an S-curve to zero at width W1, corresponding to the far right of the strip 30b as viewed in Fig. 4b.
Both the patterned reflector strips 30a and 30b have average densities of first areas that are highest mid-way along the width of the strip, and so this has the effect of concentrating the light emitted from the waveguide towards a direction extending perpendicular from the strips. The schematic diagram of Fig. 5 shows the angular distribution of light intensities when using the patterned reflective strip 30b of Fig. 4b. Specifically, the intensity of the light 3b along the plane 4b is shown in the graph 5b. The trace 6b shows that the light intensity has a large peak at 35b, corresponding to directions close to direction 7b perpendicular to the reflective strip 30b.
By comparing the trace 6b to the trace 6 of Fig. 1, it can be seen that the patterned reflective strip 30b more closely concentrates the light around the direction 7b, than the homogenous reflective strip 2 of Fig. 1 which is entirely reflective and without any patterning. The light distribution reflected from the patterned reflective strip 30a is similar to the light distribution shown in the trace 6b, however the peak in light intensity is not quite as broad as the peak 35b.
The schematic diagrams of Figs. 6a to 6c show three further alternative plan views of the waveguide 15 when looking from direction 40 marked on Figs. 2 and 3. Specifically, Fig. 6a shows a third possible option with the transparent material 20 designated as 20c and the reflective strip 30 designated as 30c, Fig. 6b shows a fourth possible option with the transparent material 20 designated as 20d and the reflective strip 30 designated as 30d, and Fig. 6c shows a fifth possible option with the transparent material 20 designated as 20e and the reflective strip 30 designated as 30e.
The patterned reflective strips 30c, 30d, and 30e the transparent material 20c, 20d, and 20e comprises first areas 61c, 61 d, and 61 e which are areas filled with reflective material, and second areas 62c, 62d, and 62e which are areas devoid of any reflective material. The first and second areas are arranged in a repetitive pattern that extends the full length of each patterned reflective strips 30c, 30d, and 30e.
The first areas of each patterned reflective strip 30c, 30d, and 30e are all the same size as one another, and are wider than they are long. They are also symmetrical about a central axis of the patterned reflective strip, the central axis aligned along the length of the patterned reflective strip, mid-way along the width of the patterned reflective strip. Each first area 61c, 61 d, and 61 e is also symmetrical about its own length, which is aligned with the length of the patterned reflective strip, and about its own width, which is aligned with the width of the patterned reflective strip.
Beneath each of the transparent materials 20c, 20d, and 20e are shown graphs with traces 100c, 100d, and 100e illustrating the average density Ds of the first areas compared to the second areas along the widths Ws of the patterned reflective strips 30c, 30d, and 30e. The trace 100c shows that the average density of first areas to second areas taken along the length of the strip immediately ramps up to a maximum at width Wo, corresponding to the far left of the strip 30c as viewed in Fig. 6a, curves down to a minimum mid-way along the width of the strip at W0.5, and curves back up to another maximum at width W1 corresponding to the far right of the strip 30c as viewed in Fig. 6a, where it immediately ramps down to zero again.
The trace 10Od shows that the average density of first areas to second areas taken along the length of the strip immediately ramps up to a maximum at width Wo, corresponding to the far left of the strip 30d as viewed in Fig. 6b, linearly ramps down to a minimum mid-way along the width of the strip at W0.5, and linearly ramps back up to another maximum at width W1 corresponding to the far right of the strip 30d as viewed in Fig. 6b, where it immediately ramps down to zero again.
The trace 10Oe shows that the average density of first areas to second areas taken along the length of the strip gradually curves up from zero at width Wo to a maximum at width W0.15, over an end portion at the far left of the strip 30e as viewed in Fig. 6c, gradually curves down to a minimum mid-way along the width of the strip at W0.5, and gradually curves back up to another maximum at width Wo.ssFrom Wo 85 to W1 the average density gradually curves back down to zero over an end portion at the far right of the strip 30e as viewed in Fig. 6c.
All the patterned reflector strips 30c, 30d, and 30e have average densities of first areas that have a minimum mid-way along the width of the strip, and so this has the effect of spreading the light emitted from the waveguide further away from the directions extending perpendicular from the strips, making the intensity of emitted light more uniform over the angles of light emission. The schematic diagram of Fig. 7 shows the angular distribution of light intensities when using the patterned reflective strip 30c of Fig. 6a. Specifically, the intensity of the light 3c along the plane 4c is shown in the graph 5c. The trace 6c shows that the light intensity is uniform along the plane 4c, and there is no peak in the light intensity in the direction 7c perpendicular to the reflective strip 30c.
The light distribution reflected from the patterned reflective strips 30d and 30e is similar to the light distribution shown in the trace 6b, however there is a more gradual drop in the level of light intensity reflected from the patterned strip 30e at the extremes of the angular range of light emission, due to the gradual increase and decrease in average density over the end portions covering Wo to Woland Wo.ssto Wi, as shown in the trace 100e.
The schematic diagrams of Figs. 8a and 8b show two further alternative plan views of the waveguide 15 when looking from direction 40 marked on Figs. 2 and 3. Specifically, Fig. 8a shows a sixth possible option with the transparent material 20 designated as 20f and the reflective strip 30 designated as 30f, and Fig. 8b shows a seventh possible option with the transparent material 20 designated as 20g and the reflective strip 30 designated as 30g.
The patterned reflective strip 30f on the transparent material 20f comprises first areas 61 f which are areas filled with reflective material, and second areas 62f which are areas devoid of any reflective material. Similarly, the patterned reflective strip 30g on the transparent material 20g comprises first areas 61 g which are areas filled with reflective material, and second areas 62g which are areas devoid of any reflective material. The first and second areas are arranged in a repetitive pattern that extends the full length of each patterned reflective strip 30f and 30g.
The first areas of each patterned reflective strip 30f and 30g are all the same size as one another, and are wider than they are long. Each first area 61 f, 61 g is symmetrical about its own width, which is aligned with the width of the patterned reflective strip.
Beneath each of the transparent materials 20f and 20g are shown graphs with traces 10Of and 100g illustrating the average density Ds of the first areas compared to the second areas along the widths Ws of the patterned reflective strips 30f and 30g. The trace 10Of shows that the average density of first areas to second areas taken along the length of the strip 30f begins at a maximum at width Wo, corresponding to the far left of the strip 30f as viewed in Fig. 8a, and linearly ramps down to zero at width Wi, corresponding to the far right of the strip 30f as viewed in Fig. 8a.
The trace 10Og shows that the average density of first areas to second areas taken along the length of the strip 30g begins at zero at width Wo, corresponding to the far left of the strip 30g as viewed in Fig. 8b, gradually curves up to a maximum at W0.15 over an end portion of the width, and gradually curves back down to zero at width W1, corresponding to the far right of the strip 30g as viewed in Fig. 8b.
Both the patterned reflector strips 30f and 30g have average densities of first areas that are highest towards an end of the width of the strip, and so this has the effect of offsetting the light emitted from the waveguide away from a direction extending perpendicular from the strips. The schematic diagram of Fig. 9 shows the angular distribution of light intensities when using the patterned reflective strip 30f of Fig. 8a. Specifically, the intensity of the light 3f along the plane 4f is shown in the graph 5f. The direction 7f is perpendicular to the patterned reflective strip 30f.
The trace 6f shows that the light intensity is substantially uniform along the plane 4f, and is maintained at a consistent level at the right side of the plane 4f as viewed in Fig. 9, even though that side of the plane is further away from the waveguide. This is because more light is emitted to the right side of direction 7f, corresponding to reflection from the left side of the patterned reflective strip 30f where the trace 10Of shows the average density is high, than is emitted to the left side of the direction 7f, corresponding to reflection from the right side of the patterned reflective strip 30f where the trace 10Of shows the average density is low. This has uses in signage applications, where the waveguide needs to be positioned along an edge of the sign as so not to obscure it.
The light distribution reflected from the patterned reflective strip 30g is similar to the light distribution shown in the trace 6f, however the light intensity at the most extreme angles of light emission towards the right side of the plane 4f will drop off more gradually for the patterned reflective strip 30g than for the patterned reflective strip 30f, due to the gradual reduction in average density at the end portion between Wo and W0.15 of trace 100g.
Fig. 10 shows a schematic cross-sectional diagram of an alternate waveguide for use in the lighting device of Fig. 2. In this alternate waveguide, the length of transparent material 20, designated as 20h, has three patterned reflector strips aligned along the length of the transparent material. In this embodiment, each one of the patterned reflective strips are the same as the patterned reflector strip 30b, so that light is concentrated to emit from the waveguide in three different directions.
In further alternatives, each one of the three patterned reflector strips may be the same as any one of the patterned reflector strips 30a, 30c, 30d, 30e, 30f, or 30g, and/or different numbers of patterned reflector strips may be aligned along the length of the transparent material. As shown, the three patterned reflector strips are arranged at regular angular intervals around the transparent material, however that does not have to be the case in alternate embodiments.
Many other variations of the described embodiments falling within the scope of the invention will be also apparent to those skilled in the art.

Claims (32)

1. A waveguide comprising a transparent material which carries light along a length of the transparent material by total internal reflection, and a patterned reflector strip on the transparent material for reflecting light out of the waveguide, wherein the patterned reflector strip has a length aligned with the length of the transparent material, wherein the patterned reflector strip comprises first areas of reflective material and second areas which are devoid of reflective material, and wherein an average density of the first areas compared to the second areas taken along the length of the patterned reflector strip, varies across a width of the patterned reflector strip.
2. The waveguide of claim 1, wherein the first areas and the second areas alternate with one another along the length of the patterned reflector strip.
3. The waveguide of claim 2, wherein the first areas and the second areas form a repetitive pattern along the length of the patterned reflector strip.
4. The waveguide of any preceding claim, wherein the first areas are all a same size as one another.
5. The waveguide of any preceding claim, wherein the second areas are all a same size as one another.
6. The waveguide of any preceding claim, wherein each first area extends fully across a full width of the patterned reflector strip.
7. The waveguide of any preceding claim, wherein each first area extends further across the width of the patterned reflector strip than it extends along the length of the patterned reflector strip.
8. The waveguide of any preceding claim, wherein each first area comprises a perimeter having an arc shaped segment.
9. The waveguide of claim 8, wherein each first area comprises two of the arc shaped segments arranged symmetrically with one another.
10. The waveguide of any preceding claim, wherein each first area has a width parallel the width of the patterned reflector strip, and a length parallel the length of the patterned reflector strip.
11. The waveguide of claim 10, wherein each first area is symmetrical about the width of the first area.
12. The waveguide of claim 10 or 11, wherein each first area is symmetrical about the length of the first area.
13. The waveguide of any preceding claim, wherein the patterned reflector strip comprises a central axis extending along the length of the patterned reflector strip, mid-way along the width of the patterned reflector strip.
14. The waveguide of claim 13, wherein the patterned reflector strip is symmetrical about the central axis.
15. The waveguide of any preceding claim, wherein the average density is at a maximum mid-way along the width of the patterned reflector strip.
16. The waveguide of claim 15, wherein the average density gradually and smoothly reduces away from mid-way along the width of the patterned reflector strip.
17. The waveguide of any preceding claim, wherein the average density is at a minimum mid-way along the width of the patterned reflector strip.
18. The waveguide of claim 17, wherein the average density gradually and smoothly increases away from mid-way along the width of the patterned reflector strip.
19. The waveguide of claim 18, wherein the average density gradually and smoothly reduces to zero over opposing end portions of the width of the patterned reflector strip, subsequent to the gradual and smooth increase away from mid-way along the width of the patterned reflector strip.
20. The waveguide of any one of claims 1 to 11, wherein the average density gradually and smoothly increases along a portion of the width of the patterned reflector strip, the portion having a middle region including mid-way along the width of the patterned reflector strip width.
21. The waveguide of claim 20, wherein the average density has a maximum at a first end portion of the width of the patterned reflector strip, and wherein the average density continuously reduces from the maximum to a minimum at a second end portion of the width of the patterned reflector strip, the second end portion opposite from the first end portion.
22. The waveguide of claim 21, wherein the first end portion has an end where the average density reduces to zero, and wherein the average density gradually and smoothly increases to the maximum along the first end portion.
23. The waveguide of any one of claims 19, 21, or 22, wherein each end portion comprises no more than 20% of the width of the patterned reflector strip.
24. The waveguide of any preceding claim, wherein the patterned reflector strip is on or adjacent an exterior surface of the length of transparent material.
25. The waveguide of claim 24, wherein the patterned reflector strip is formed as a coating on the exterior surface of the length of transparent material.
26. The waveguide of any preceding claim, wherein the patterned reflector strip extends along substantially a full length of the length of transparent material.
27. The waveguide of any preceding claim, wherein the transparent material is in the shape of a cylinder.
28. The waveguide of any preceding claim, wherein the transparent material is an acrylic material.
29. The waveguide of any preceding claim, wherein there are a plurality of the patterned reflector strips arranged parallel to one another along the length of the transparent material.
30. The waveguide of claim 29, wherein the plurality of patterned reflector strips are spaced apart from one another at regular intervals to emit light at regular angular intervals around the transparent material.
31. A lighting device comprising the waveguide of any preceding claim and a lamp mounted adjacent an end of the waveguide, the lamp for emitting light into the end of the waveguide.
32. The lighting device of claim 31, wherein the lamp comprises one or more Light Emitting Diodes.
GB1716389.0A 2017-10-06 2017-10-06 A waveguide and lighting device comprising the waveguide Withdrawn GB2568864A (en)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20110249214A1 (en) * 2010-04-13 2011-10-13 Samsung Electronics Co., Ltd Backlight assembly and display apparatus having the same
US20130135853A1 (en) * 2011-11-29 2013-05-30 Chi-Feng Lin Light-guiding element, light-emitting diode lamp tube and illumination lamp

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20110249214A1 (en) * 2010-04-13 2011-10-13 Samsung Electronics Co., Ltd Backlight assembly and display apparatus having the same
US20130135853A1 (en) * 2011-11-29 2013-05-30 Chi-Feng Lin Light-guiding element, light-emitting diode lamp tube and illumination lamp

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