The present invention relates to the field of lighting panels. In particular, a lighting panel device for illumination, lighting and display purposes is described that exhibits a light output having a definable narrow beam profile and definable beam angle.
Light Emitting Diodes (LEDs) are high efficacy and highly reliable examples of solid state light sources. As the cost benefits of solid state lighting improve, this technology is gradually replacing older lighting technologies, such as fluorescent lamps, in a wide variety of professional and consumer applications. LEDs are comparatively small sources of light and therefore generally employ external optics to provide a useful lighting system. It is important that the external optics, in conjunction with the performance specification of the LED, provides the desired function with a high optical efficiency. A high optical efficiency is needed so as to minimise cost (both unit and running), to minimise heat dissipation and to maximise energy efficiency credentials.
It is known to employ LEDs within a spot light type system so as to provide an output that exhibits a narrow profile and which has a definable beam angle. An example of such a system is presented schematically in
Another more recent approach to LED lighting is to couple the LEDs to light-guide plates. This is used to give a thin luminaire panel with a large area of diffuse lighting. Examples of such devices are provided by the inventor within PCT Publication No. WO 2005/101070 and presented schematically in
Commercially available examples of such systems may typically comprise 600 mm×600 mm sized panels that have LEDs located around the four edges of a sheet of a polymer light-guide plate. In practice it is found that as a result of the design of these systems the light output generated exhibits a very wide beam angle typically lambertian (120° Full Width Half Maximum). These systems are well suited for many applications however their designs do exhibit a number of limitations which makes them unsuitable for other types of applications.
In the first instance the optical coupling losses between the LEDs 8 and the light-guide edge, in combination with the large average optical path lengths of the light 10 within the absorbing transparent polymer of the panel 9, results in a system that exhibits significant optical loss. This optical loss impacts on the overall optical efficiency of the systems which is known to be as low as 50%.
The most common polymer material employed as the transparent light-guide plate 9 is acrylic (PMMA) due to this material having the highest optical transparency. However, compared with many other transparent materials (e.g. silicone), acrylic is not stable at high temperatures and high light power levels. Over time, the acrylic material is known to discolour and so light transmission is reduced. This is particularly evident in the areas closest to where the LEDs 8 are positioned, as they have the highest temperature and highest light power levels. These effects limit the working life-time of such products based on an acrylic light-guide. For lighting applications, where LEDs are promoted to have long life-times, this is a major disadvantage.
For applications where a particular beam angle distribution is required the wide, and usually lambertian, angular distribution of the output light provides further disadvantages. In such applications additional external films must be deployed, thus reducing further the optical efficiency, increasing production costs and providing general integration difficulties.
It is therefore an object of an aspect of the present invention to obviate or at least mitigate the foregoing disadvantages of the LED based light source systems known in the art.
It is a further object of an embodiment of the present invention to provide an LED based lighting panel that exhibits an output having a narrow output beam profile.
A yet further aspect of an embodiment of the present invention is to provide an LED based lighting panel that exhibits a predetermined output beam angle.
In the following description the terms transparent refers to the optical properties of a component of the lighting panel at the wavelengths of the light generated by the LED light sources employed within the apparatus.
According to a first aspect of the present invention there is provided a lighting panel the lighting panel comprising a transparent substrate upon a first surface of which are mounted a plurality of transparent prism structures and upon a second surface of which is mounted a light emitting diode (LED), and a transparent guide layer, the guide layer being arranged so as to encapsulate the LED upon the second surface such that the transparent base substrate and the transparent guide light form a composite structure for guiding light emitted from the LED, wherein the plurality of transparent prism structures are configured to extract a first and a second light output from the lighting panel, the first and second light outputs having output angles and beam widths determined by the plurality of transparent prism structures.
The lighting panels effectively provide an alternative means for producing a “spot light” like illumination from an LED. Having the LED embedded within the devices also provides the added advantage of significantly improving the optical coupling of the light into the guide layer while allowing the overall thickness of the device to be reduced. Embedding the LED source also provides them with physical protection while allowing for improved thermal dissipation. The lighting panels therefore exhibit high optical efficiencies and long operating lifetimes.
The plurality of transparent prism structures extract the first and second light output from the lighting panel by disrupting internal reflection effects within the composite structure.
Preferably the first and second light outputs are extracted from opposite sides of the lighting panel.
Most preferably the plurality of transparent prism structures are configured to compress the light emitted from the LED. In this context compression means that the width of the first and second light outputs is narrower than the width of the light emitted from the LED.
Most preferably the lighting panel further comprise a transparent coating layer applied to the plurality of transparent prism structures wherein the transparent coating layer provides a further means for determining the output angles of the first and second light outputs.
Preferably the transparent coating is applied to the plurality of transparent prism structures so as to form a substantially planar surface. Having a substantially planar surface reduces the tendency for dirt or dust to settle on the exposed surface.
Optionally, the transparent coating comprises a spatial pattern e.g. lined or chequered patterns. The spatial pattern acts to providing two components to both the first and second output beams. The resulting light intensity distribution is therefore a superposition of these two components of the first and second output beams.
Optionally the lighting panel further comprises a reflector arranged so as to reflect the first light output back through the composite structure. In this embodiment the first light output is effectively combined with the second light output.
The reflector may comprise an array of apertures. The array of apertures may be a regular array of apertures. The apertures may comprise a regular geometrical shape e.g. they may be circular.
The reflector may comprise a transparent film and a plurality of patterned reflective or optical features. In this embodiment the reflector provides a means for controlling the proportion of light emitted within the first and second light outputs. It may also provide a means to further control the light beam profile and output angle of the first and second outputs.
Optionally the lighting panel further comprises a second LED mounted upon the second surface of the transparent substrate such that light emitted from second LED is guiding through the composite structure in a separate direction to that of the light emitted by the first LED. In this embodiment the configuration of the plurality of transparent prism structures acts to extract a third and a fourth light output from the lighting panel.
Preferably the light emitted from second LED is guiding through the composite structure in an opposite direction to that of the light emitted by the first LED.
The transparent substrate preferably has a refractive index ns between 1.50 and 1.66.
The transparent prism structures preferably have a refractive index np between 1.46 and 1.58.
The transparent guide layer preferably has a refractive index ng between 1.46 and 1.56.
The transparent coating layer preferably has a refractive index nc between 1.37 and 1.58.
Most preferably the refractive indices of the transparent substrate and the transparent prism structures are selected such that they satisfy the inequality ns≧np.
Most preferably the refractive indices of the transparent substrate and the transparent guide layer are selected such that they satisfy the inequality ns≧ng.
Most preferably the refractive indices of the transparent prism structures and the transparent coating layer are selected such they satisfy the inequality np≧nc.
According to a second aspect of the present invention there is provided a method of producing a lighting panel the method comprising:
Optionally the method of producing a lighting panel further comprises applying a transparent coating layer to the plurality of transparent prism structures wherein the transparent coating layer provides a further means for determining the output angles of the first and second light outputs.
Preferably the transparent coating is applied to the plurality of transparent prism structures so as to form a substantially planar surface.
Optionally the method of producing a lighting panel further comprises arranging a reflector so as to reflect the first light output back through the composite structure.
Optionally the method of producing a lighting panel further comprises mounting a second LED mounted upon the second surface of the transparent substrate such that light emitted from second LED is guiding through the composite structure in a separate direction to that of the light emitted by the first LED.
Preferably the second LED is mounted upon the second surface of the transparent substrate such that light emitted from the second LED is guiding through the composite structure in an opposite direction to that of the light emitted by the first LED.
Embodiments of the second aspect of the invention may comprise features to implement the preferred or optional features of the first aspect of the invention or vice versa.
Aspects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the following drawings in which:
In the description which follows, like parts are marked throughout the specification and drawings with the same reference numerals. The drawings are not necessarily to scale and the proportions of certain parts have been exaggerated to better illustrate details and features of embodiments of the invention.
Referring initially to
Located on a first surface 16 of the transparent substrate 15, is an array of 90° prism structures 17, also formed from a transparent plastic polymer and having a refractive index np between 1.46 and 1.58. The refractive indices of the transparent substrate 15 and the transparent prism structures 17 are selected such that they satisfy the inequality ns≧np.
The substrate 15 and the prism structures 17 can be provided as a single commercial product, a Vikuiti™ brightness enhancement film (BEF III) being an example of such a product employed within the presently described embodiment. In this product the substrate has a thickness of approximately 127 microns while the prism structures 17 have a thickness of approximately 28 microns. The refractive index n, of the substrate 15 is selected to be 1.61 while the refractive index np of the prism structures 17 is chosen to be 1.58.
Located on a second surface 18 of the substrate 15, the second surface 18 being opposite the first surface 16, is a side emitting LED 19 whose output has a lambertian distribution (120° full width half maximum), a Nichia® 206 LED being an example of a suitable LED device. Electrical tracking (not shown in
Covering the LED 19 and the remaining area of the second surface 18 of the substrate 15 is a guide layer 20, also formed from a transparent plastic polymer, and having a refractive index ng between 1.46 and 1.56. The refractive indices of the transparent substrate 15 and the transparent guide layer 20 are selected such that they satisfy the inequality ns≧ng. In order to satisfy this inequality the presently described embodiment employs a transparent guide layer 20 having a refractive index ng of 1.51.
As a result of the above arrangement and choice of the refractive indices ng, ns and np light 21 generated by the LED 19 is initially coupled into the transparent guide layer 20, so as to propagate in a direction substantially parallel to a plane defined by the transparent substrate 15, as shown on
When the light 21 interacts with the transparent prism structures 17, this acts to disrupt or overcome the effects of total internal reflection within the combined structure formed from between the transparent guide layer 20 and the transparent substrate 15. As a result, the light 21 is redirected so as to exit the lighting panel 14 via the transparent prism structures 17, as a first light output as depicted by reference numeral 22, or via the transparent guide layer 20, after propagating back through the transparent substrate 15 and the transparent guide layer 20, as a second light output as depicted by reference numeral 23.
It is the form of the prism structures that determines the output angles and beam widths of the first 22 and second 23 light outputs. Indeed the presence of the prism structures 17 act to increase the on-axis brightness of the first 22 and second 23 light output beams by compressing the light into a narrower viewing angle. This compression of the light output beams 22 and 23 can clearly be seen within the transverse beam profile measurement (solid line) for the lighting panel 14 presented in
a) presents a side view of the lighting panel 14 of
It will be appreciated by those skilled in the art that the reflector 24 could be orientated on the opposite side of the lighting panel 14, to its position shown in
A top view of an alternative reflector 24b is presented in
In a further alternative embodiment the reflector 24 or 24b may comprise a transparent film with patterned reflective or optical features to control the proportion of light or further control the light beam profile and angle. In particular, locating the features on or around the LED positions can provide a means for reducing the glare or so-called “sparkle” as viewed by an observer.
A further alternative embodiment of the lighting panel 14b is presented in
Further detail of the light output from the lighting panel 14b of
The ability to further control the output beam angle of the light outputs 22, 23 and 27 from the lighting panels 10 and 14b will now be described with reference to
As a result of the introduction of the coating layer 29, the beam angle of the first light output 22 from the lighting panel 14c is increased from 60° to 70° while that of the second light output 23 is increased from 25° to 50°. This effect is further illustrated by the beam profile measurement profile presented in
It is preferable that the coating layer 29 is added to the prism structures 17, so as to form a substantially planar surface. As a result, the second light output 23 is refracted by the combination of the prism structures 17 and the coating layer 29, and not just the coating layer 29 as may be expected to the non-informed observer. A further advantage of employing the coating layer 29 to form a substantially planar surface, is that such a surface is less likely to collect dirt or dust when compared to that of the prism structures 17 in isolation.
As will be appreciated by the skilled reader, the refractive index of the coating layer 29 can be selected so as to achieve the desired output angles for the beams 22 and 23, and may of course be employed in conjunction with the reflective layer 24, as previously discussed with reference to
In order to demonstrate the scalability of this device
The above described embodiments provide lighting panels 14, 14b, 14c and 14d that produce narrowed beam angular distributions from wide angle (lambertian) LED sources. This is achieved by the employment of the transparent layer of prism structures 17.
Furthermore, by embedding the LEDs 19 and 26 within the devices 14, 14b, 14c and 14d also provides the added advantage of significantly improving the optical coupling of the light 21 into the guide layer 20. This configuration also allows for the LEDs 19 and 26 to be located anywhere across the first surface 16 of the transparent substrate 15 thus providing a means for significantly reducing the average optical path length of the light 21. The combination of both of these features results in systems that exhibit high optical efficiencies when compared to the lighting panel systems known in the art.
The described structures also have the further advantage in that they enable the use of more stable transparent optical polymers in the vicinity of the LEDs 19 and 26. They also act to distribute the thermal dissipation evenly over the entire area of lighting panels 14, 14b, 14c and 14d, rather than just at the edges as found within the edge coupled prior art systems, see
The above embodiments have all been described with reference to the employment of 90° prism 1-dimensional structures 17. It will however be appreciated by the skilled reader that other angled prism structures could equally well be employed. Different output beam profiles and angle widths can also be obtained by employing different shaped prism structures, for example, lenses, micro-lenses, 2-dimensional prism pyramid structures or saw-tooth (asymmetric prisms), holographic and other diffractive or refractive structures. These can have a regular distribution or random distribution.
A further advantage of the above described lighting panels 14, 14b, 14c and 14d, is that narrow beam widths can be achieved from a wide beam angle light source 19 and 26 in a very thin device in a direction generally perpendicular or off-axis compared to the direction of the light emitted from the LED sources 19 and 26. The described lighting panels 14, 14b, 14c and 14d, have typical thicknesses of around 2 mm. This allows for thin lighting panels to have directed and focused light delivery without any additional external components, such as beam control films being required. This acts to significantly improve the optical efficiency, reduce system costs and ease of manufacture, integration and installation. By way of example, in room lighting, a panel deployed as a thin layer on the floor can produce a focused beam efficiency delivered up onto an adjacent wall. Previously, thick and bulky spotlight types of devices, as presented in
In addition, the described devices 14, 14b, 14c and 14d can be given added functionality by adding a coating layer 29 onto the light extraction surface features 17, which then function to modify the output beam angle of the output light 22, 23 and 27. This layer 29 is selected to have a lower refractive index than the surface extraction features 17, but higher than that of air and so acts to increase the angle of distribution from the normal direction. The benefit of this approach is that it gives an easy manufacturing control of the output beam angles for a fixed substrate surface feature in the light panel structure. This avoids the costly requirement of producing a new light extracting feature design (prisms with different angles) for each required product beam angle.
A lighting panel that provide an alternative means for producing a “spot light” like illumination from an LED is described. The lighting panel comprising a transparent substrate upon a first surface of which are mounted a plurality of transparent prism structures and upon a second surface of which is mounted a light emitting diode (LED). A transparent guide layer is arranged so as to encapsulate the light emitting diode upon the second surface such that the transparent base substrate and the transparent guide light form a composite structure for guiding light emitted from the LED. The transparent prism structures are configured to extract a first and a second light output from the lighting panel, the first and second light outputs having output angles and beam widths determined by the structure of the plurality of transparent prism structures. The lighting panels exhibit high optical efficiencies and long operating lifetimes.
The foregoing description of the invention has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The described embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilise the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, further modifications or improvements may be incorporated without departing from the scope of the invention as defined by the appended claims.
Number | Date | Country | Kind |
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1204167.9 | Mar 2012 | GB | national |
Filing Document | Filing Date | Country | Kind |
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PCT/GB2013/050584 | 3/8/2013 | WO | 00 |