Patent Application
20150176810
This invention relates to a directional luminaire (for example a spot or accent light) capable of providing light in an indoor or outdoor environment. It further refers to spotlights that can have a thin profile and to those that require reduced glare. This luminaire has the further capability of providing angle and direction-controlled illumination.
This application claims priority of U.S. Provisional Application No. 61/673,902 filed on Jul. 20, 2012 and U.S. application Ser. No. 13/563,117 filed on Jul. 31, 2012, which are incorporated herein by reference in its entirety.
Directional luminaires such as spotlights, accent lights, downlighters, etc. are used in a wide variety of applications in residential, commercial and industrial premises. They are used particularly where a high surface brightness is required such as task lighting in kitchens and in retail accent lighting. These luminaires, at the basic level, consist of two components: a light engine, which generates light and an optic that collimates light emitted by the light engine. Most light engines, and all common ones like tungsten Halogen, HID, LED, CFL, OLED etc. emit with a very broad angular distribution (isotropic or Lambertian). The optic then collimates this light into the required directionality. This in turn increases the luminous intensity of the luminaire allowing higher brightness in smaller areas.
The most common and simplest form of optic is a reflector cup and can take many forms, such as a TIR optic or metal reflector, and these are commonly known.
To make an effective spotlight the etendue of the system must be conserved, hence the light engine emitting area must be much smaller than the reflector output front area. Hence a small point-like light source is ideal. This is often not the case with CFL or OLED, but is possible with LED. The optic also needs to capture and redirect as much light as possible from the source, which means that the reflector also must have a significant thickness relative to the aperture area, a greater thickness if the collimation is greater.
Modern designs of lighting systems often now require thin or flat lighting structures and necessarily it has been very difficult to make a directional light source that is very thin. Bright low thickness spotlights have typically used many small light sources with small reflectors. For bright applications there are limitations on LED size, hence front aperture and thickness and for typical spotlights, a minimum optic thickness has tended to be around 12-14 mm before significant losses in efficiency occur.
In addition, small or point-like light sources, although often convenient in terms of size, weight, and ability to integrate into a luminaire, often have a disadvantage from a users' point of view in that the light is emitted from a small area; even if not dangerously bright, if viewed directly or in peripheral vision a small source can be uncomfortable to look at, and this is known as glare. Large area luminaires are desirable in some circumstances because they allow a small source of a given brightness to emit over a larger surface area, thus reducing the perceived surface brightness, and increasing the visual comfort of the light source. Lightguide luminaires are commonly known in both lighting and display backlight applications as a way to create a large area light source from one or more small or point-like light sources. In their most common form, light is in-coupled from a source to a material such as a transparent plastic (PMMA, acrylic, or similar) or glass, and is then transported through the material by total internal reflection (TIR), and only out-coupled when it encounters an out-coupling feature designed to frustrate TIR. These lightguides are inexpensive and easy to manufacture, but particularly for larger examples, the material used makes them heavy. In addition, the angular distribution of light emitted from the lightguide is normally non-optimal for the intended purpose and requires multiple extra optical films to turn the light into the desired emission directions.
An alternative approach is to fabricate a reflecting cavity. This approach is adopted in U.S. Pat. No. 7,726,828 (Sato, Jun. 1, 2010). With reference to
In EP2163807 (Sato, Mar. 17, 2010), as U.S. Pat. No. 7,726,828, the large area light source is formed of a reflecting cavity, as seen in
In U.S. Pat. No. 7,494,246 (Harbors, Feb. 24, 2009) multiple LEDs are distributed in a reflective cavity as shown in
In EP 2312199 (Sato, Aug. 6, 2008) a directional light source is used to obtain a large flat surface source using a pattern of holes that allow more transmission further from the light source.
In general out-coupling light from lightguides and reflection from diffuse reflectors is not a good way of providing precise control over the angular properties of emitted light from a lightguide or luminaire; approximate beam shaping in extraction from lightguides is possible by the careful design of extraction features, but in general for more precise beam-shaping additional optical films (such as brightness enhancement films) are needed. Diffuse reflectors cause diffuse reflection of light, and thus emission from a luminaire employing diffuse reflection as the primary means of light propagation will be approximately Lambertian in distribution. This is necessarily a requirement of the rule of etendue, whereby for all “normal” geometrical optics, the product of area and mean solid angle of emission is a constant.
One solution is to use lenses or mirrored reflectors, however, these components must be bigger than the source for strong collimation and by their nature, must be physically separated from the source along the beam path, hence a thick optical component.
A device and method in accordance with the present invention involves a different type of optic that provides four key features, where all do not exist together in the prior art. These are:
The optic includes a cavity with one or more light sources (e.g. LED) placed in it. The cavity is lined with high reflectivity material (e.g. interference film or a metallised layer). Around each light source the surface slopes upwards at a small angle around the source. The top surface of the cavity consists of a series of patterned holes or apertures that are designed to maximize luminous intensity, efficiency or other characteristic.
Light form the light sources reflects a number of times from the sides and exits the cavity through the holes. The angle to the lower surface changes the angle of the light such that the light becomes more collimated before exiting the cavity. This results, with an appropriate pattern of apertures, in a luminaire with a controlled angular distribution.
The low angle of the surface and the fact that the light reflects a number of times means that the thickness of the optic can be substantially thinner than a simple reflector using the same number of light sources.
The light also exits the cavity through the array of holes hence achieving a wide area narrow beam source.
The light source is then not seen directly and the light is spread enabling a lower retinal brightness from the luminaire and hence a reduced glare capacity.
An alternative embodiment is in the use of a light source that is already directed and without a slope to the lower surface of the cavity. In this case a directed light source is a light source that is already of a collimated character, either intrinsically (e.g. a laser) or an LED that has a optic already present (e.g. a smaller reflector cup) separate from the invention optic. This also refers to the case where the light receiving surface of the inventive optic applies a collimated character to the light (e.g. a curved lens-like surface).
In using a specular reflector, the light emitted from the source will travel in straight lines radially outwards. This introduces an extra, important, constraint in determining the position of holes in the surface of the luminaire; not only is the hole density defined as a function of radius, but also holes are carefully placed as a function of radius and angle to ensure that emission from holes at larger radii is not obstructed or shadowed by holes at smaller radii.
Thus, a device and method in accordance with the present invention can use a specular reflector in combination with a light source of specified angular emission characteristics. The reflector is formed into a cavity surrounding the light source, and holes are formed through which the light is extracted from the cavity. Through the use of a specular reflector, the angular properties of the source are preserved on extraction from the cavity. Holes are placed in order that the light is extracted uniformly over the surface of the reflecting cavity, and further, hole position is determined such that holes at larger radii are able to extract sufficient light and are not shadowed by extraction from holes at smaller radii.
Further aspects of the invention concern additional optical features which may be used to steer light inside the cavity, either by modifying the cavity walls such that the angle of light rays inside the cavity is altered on reflection with the cavity walls, or by introducing new optical features within the cavity.
The use of multiple directed light sources (or light sources with different surrounding slopes) can then be used to create a luminaire with modifiable angular emission characteristics either in angular spread or in direction from the luminaire, or both together.
The embodiments of this invention are summarized as applying to luminaires for general lighting but similarly the same technology can be used for uniform backlighting for display panels such as liquid crystal displays. The methods described here can produce collimated or controllable backlighting for phone, monitor, TV or signage applications. In the case of the luminaire application, the brightness and distribution is important. In the case of a display illumination application uniformity is also important.
According to one aspect of the invention, a lighting device includes: a transparent optical cavity including an exit surface including a specularly reflective material arranged to reflect light into the cavity, the exit surface having a plurality of apertures formed therein, a base surface including a specularly reflective material arranged to reflect light into the cavity, and at least one light receiving surface arranged relative to the base surface and configured to receive light from a light source, wherein the plurality of apertures are arranged to maximize at least one of uniformity, angular distribution, efficiency or luminous intensity of light exiting the exit surface, and wherein a distribution of light received at the light receiving surface is altered by at least one of a combination of the exit surface and the base surface, or the light receiving surface.
According to one aspect of the invention, a method of providing glare-free light in a predefined area having at least one pre-existing light source arranged therein includes arranging the light receiving surface of the lighting device described herein relative to the pre-existing light source so as to receive light emitted by the preexisting light source at the light receiving surface.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
In the annexed drawings, like references indicate like parts or features:
a shows possible structural realizations of the first embodiment.
b shows possible structural realizations of the first embodiment.
a illustrates an exemplary a light source with emission distribution which is not symmetric about the luminaire normal axis in accordance with a fourth embodiment of the invention.
b illustrates an exemplary a light source having multiple LEDs with differing angular distributions in accordance with an embodiment of the invention.
a illustrates an exemplary luminaire where a reflective cavity is retrofit over an external light source in accordance with a seventh embodiment of the invention.
b illustrates an exemplary luminaire where a reflective cavity is retrofit over an external light source in accordance with a seventh embodiment of the invention.
c illustrates an exemplary luminaire where a reflective cavity is retrofit over an external light source in accordance with a seventh embodiment of the invention.
a illustrates exemplary optical features used for light steering.
b illustrates exemplary optical features used for light steering.
a illustrates use of optical features for light steering in directions out of the plane of the reflective cavity in accordance with a tenth embodiment of the invention.
b illustrates use of optical features for light steering in directions out of the plane of the reflective cavity in accordance with a tenth embodiment of the invention.
a illustrates an embodiment using a diffuser or scattering medium beneath the exit surface.
b illustrates an embodiment using a diffuser or scattering medium on top of the exit surface.
c illustrates an embodiment using a perforated diffuser or scattering medium on to of exit surface.
A lighting device in accordance with the present invention includes a transparent optical cavity having an exit surface, a base surface and a light receiving surface formed in or relative to the base surface. The exit surface and the base surface include a specularly reflective material, and a plurality of apertures are formed in the exit surface, wherein the apertures are arranged to maximize at least one of uniformity, angular distribution, efficiency or luminous intensity of light exiting the exit surface. Further, at least one of a combination of the exit surface and base surface, or the light receiving surface alters a distribution of light received at the light receiving surface.
The optic consists of a cavity, 40, which can be air filled or can be a transparent optical material such as PMMA (Poly(methyl methacrylate)). The cavity includes a base surface 40a shaped with a slope, 120, extending away from the light source (e.g., sloping toward the exit surface). If the light source is point-like, then the slope is circularly symmetric about the source. If the source is linear, then the slope is also linear away from the source.
The slope, 120, may be straight or may be curved. The curve may be a conic section, in particular a section or arc from a circle, ellipse or parabola in cross section.
The cavity has end pieces, 48 (also referred to as light receiving surface 48), that can be straight or lens shaped and are specularly or diffusely reflecting (e.g., the end pieces may have a lens shape thereby providing a curved reflector). The top surface, 121, consists of a specularly reflecting area with apertures 43 cut into the surface. The apertures consist of a pattern of holes whose size and distribution vary with distance and angle away from the light source. The top surface of the top reflector (away from the light source) need not be reflecting and may be any colour as it will not affect the performance of the device.
The specular reflecting surface may include interference film (such as the commonly available ESR film) or a metallised reflecting layer such as silver or aluminium.
The optic works by reflecting and recycling light between the top reflector 121 and the slope reflector 120 such that the light is collimated. The light is out-coupled from the cavity by the holes 43 in the top reflector and proper positioning of these holes can be done to optimize both overall efficiency, surface emitted light uniformity (both apparent and actual), angular distribution and the peak luminous intensity as a function of slope angle, thickness and light source size. A simulated example of the emitted angular distribution is shown in
Overall efficiency is defined as the ratio of emitted energy over all angles to the optical or electrical energy being input.
Luminous intensity is the brightness per unit solid angle of the light in candelas or watts per steradian from the luminaire.
Angular distribution is the variation of luminous intensity with angle away from the surface normal. For cylindrically symmetric luminaires this will be a function only of the polar angle.
Surface uniformity is defined as the ratio of maximum to minimum luminance per unit area of the emitting surface of the luminaire. It can be actual, where all light is taken into account, or apparent, which is from the point of view of a distant observer of the surface. A large area of emission with high apparent uniformity will result in low retinal illumination and hence low glare, even if the luminous intensity is high. Current spotlights using reflectors typically have very non-uniform distributions.
There may be a small area around the LED where the bottom surface is parallel to the top surface (not illustrated).
It is possible also for the top (exit) surface to be curved or sloping rather than the bottom surface as this would have the same effect on the collimation of the reflected light. For example, the exit surface can be configured to slope toward the base surface and the light receiving surface.
Two methods for the construction of the luminaire are shown in
Another method of construction is shown in
The screw mounting 124 can also be used to “tune” the angular distribution to a desired level by allowing the user to move the top reflector closer to or further from the light source.
The LED may be glued onto the cavity material so as to form a continuous optical medium or there can be an air gap between the LED and cavity material.
Heatsinking for this luminaire can be done by known methods and can be integrated with the supporting structure of the luminaire.
Subsequent embodiments will be described relative to the preferred embodiment and will be described in reference to this embodiment.
An illustration of the problem of hole shadowing is shown in
d=2*h*tan(Ø) [Math.1]
where h is the height (vertical spacing) of the cavity. If the hole diameter is greater than d, all rays along the radial path through the centre of the hole will be out-coupled, and because reflections are specular that path will not be replenished; any further holes along the same path will not produce any rays. One way to prevent hole shadowing is illustrated in
A further embodiment is illustrated in
A further embodiment is illustrated in
Control of the LEDs 41a,b,c is done with a control unit 112 that can be manually controlled or automatic, for example as a tracking mechanism with a separate camera. Activation of the independent LEDs would create a directional control to the luminaire as a whole.
A further embodiment uses the principle of a specularly reflecting cavity outlined in the embodiments above to create a collimated backlight for display devices. To achieve this, collimated light sources are used to provide the light emitted into the cavity. These light sources could be single reflection LEDs (SRLEDs), 130, with reflectors, 131, to provide the desired angular properties, as illustrated in
A further embodiment concerns the determination of hole size and spacing in the previous embodiments, to further ensure visual comfort. Optionally, hole size and spacing may be designed with an additional constraint specifically to prevent the holes being individually resolvable at a given distance.
D=tan(1.7×10−3)×V
For example, at 1 meter viewing distance a spatial resolution of D=1.7 mm between holes would correspond to an angular separation of 1.7 milliradians. Accordingly, the spacing D between holes is preferably selected such that D<tan(1.7×10−3)×V. A further embodiment uses the concept of a reflective cavity with holes for out-coupling light, as described in earlier embodiments, but retrofits this over an existing light, 170. In this regard, greater uniformity and hence reduced glare lighting may be provided in a predefined area that has one or more pre-existing light sources. For example, a reflective cavity can be formed as described herein, and the cavity can be placed in optical communication with the at least one pre-existing light source. The result is a larger area luminaire, but with the same angular emission properties as the original light source. This is illustrated in
This would be useful to reduce harsh glare from downlights and to soften lighting within a room. This can be especially useful for elderly people whose glare response is reduced even though they need high brightnesses of light to maintain visual acuity. This is especially true of some visual disorders such as glaucoma or AMD.
Attachment methods of these optics, 171, can be by screw ring, clamp or other attachment method and can be designed to attach to MR16, PAR or other spotlight or downlight structures.
A further embodiment, shown in
A further embodiment concerns additional deflecting optical features, 190, that may be located between the top and bottom reflective planes within the reflective cavity described in the previous embodiments. This is especially applicable to the embodiment with parallel top and bottom surfaces. The purpose of these features is to interrupt the straight line paths taken by rays in the plane of the luminaire (the plane perpendicular to the luminaire normal axis x-x′). The principle is illustrated in
A further embodiment relates to deflecting optical features, 210, within the reflecting cavity described in previous embodiments. In this embodiment, the surface normals of the optical faces of the deflecting optical features are not necessarily perpendicular to the luminaire normal axis. If this is the case, the angle of the light rays, 211, relative to the luminaire normal axis will be altered after passing through a deflecting optical feature. This is illustrated in
A further embodiment is illustrated in
In a further embodiment, additional optical elements can be attached to the bottom or top of the exist surface.
Due to the presence of holes at the exit surface some light rays from the LED can travel through the holes at high angles without interacting with the reflector surfaces in the cavity. Such light rays do not contribute to the brightness of the central light spot and my cause extra glare for the viewer.
According to one aspect of the invention, the base surface slopes away from the light source or the exit surface slopes toward the base surface.
According to one aspect of the invention, the base surface is parallel to the exit surface.
According to one aspect of the invention, the light receiving surface comprises at least one of a lens or a curved reflector.
According to one aspect of the invention, a size and distribution of the apertures vary with distance and angle away from the light receiving surface.
According to one aspect of the invention, adjacent apertures are angularly offset from one another.
According to one aspect of the invention, the plurality of apertures are arranged on the exit surface such that at least part of each aperture lies on a radial path from the light receiving surface with no apertures present at smaller radii on the path.
According to one aspect of the invention, the device includes the light source arranged relative to the light receiving surface.
According to one aspect of the invention, light emitted by the light source travels in straight radial paths away from the light source in a plane perpendicular to an axis normal to the exit surface.
According to one aspect of the invention, the device includes a variable emission angle source configured to vary an angle of light emitted from the lighting device.
According to one aspect of the invention, the light source is configured to have an emission distribution that is non-symmetric about an axis that is normal to the exit surface.
According to one aspect of the invention, the device includes a plurality of light sources each having differing angular distributions of light, each of the plurality of light sources being individually controllable.
According to one aspect of the invention, the light source comprises a collimated light source.
According to one aspect of the invention, the light source comprises a plurality of light sources each arranged along an edge of the cavity, each of the light sources configured to emit light along an optical axis that is non-parallel to an axis normal to the exit surface.
According to one aspect of the invention, at least some of the light sources are configured to emit light along an axis parallel to the exit surface.
According to one aspect of the invention, the device includes an optical film arranged over the cavity and configured to alter a direction of light emitted from the cavity.
According to one aspect of the invention, for a predetermined viewing distance V a spacing D between adjacent holes is defined by D<tan(1.7×10−3)×V.
According to one aspect of the invention, the device includes a plurality of light sources.
According to one aspect of the invention, the device includes a plurality of deflecting optical features arranged within the reflective cavity, the deflecting optical features configured to interrupt a path of light rays that are in a plane perpendicular to a plane normal to the exit surface.
According to one aspect of the invention, a surface normal of optical faces of the deflecting features is non-perpendicular to an axis that is normal to the exit surface.
According to one aspect of the invention, the deflecting optical features comprise a continuous geometry.
According to one aspect of the invention, the light source comprises a light emitting diode (LED).
According to one aspect of the invention, the lighting device includes a scattering or diffuser medium, wherein the scattering or diffuser medium is between the base surface and the exit surface, or the exit surface is between the base surface and the scattering or diffuser medium.
According to one aspect of the invention, the scattering or diffuser medium comprises apertures corresponding to apertures in the exit surface, the apertures including sloped sidewalls to minimize light interaction at the exiting the optical cavity.
According to one aspect of the invention, a backlight comprises the lighting device described herein.
According to one aspect of the invention, a spotlight comprises the lighting device described herein.
Although the invention has been shown and described with respect to a certain embodiment or embodiments, equivalent alterations and modifications may occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.
This invention could be utilized in both residential and commercial environments. Spotlights are an increasing use in retail in particular and this invention could allow increased design freedom. Because of the use of the hole pattern, a unique brand image to the luminaire can be created. It is also possible to update existing luminaires with this structure in order to “retrofit” such adaptors onto existing structures. The relative simplicity of the design requires minimal rewiring, and in some cases may be compatible with existing light fixtures. In the case of reduced glare through better uniformity while maintaining brightness when compared to smaller spotlights or downlights this should be particularly suited for lighting for the elderly. Thus, a key market may be lighting located in hospitals, care homes, and similar environments.
The invention can also be used for collimated backlighting for displays encompassing a spatial light modulator, such as a liquid crystal panel. The layer can be used with an array of collimated light sources (that may have the same or different collimation properties and can be individually controllable) in such a manner as to create a uniform plane of collimated light that is closer to the light sources than would otherwise be the case with just air. This would allow a thinner display that can be designed to have electrically switchable angular distribution and/or angular directionality.
The light sources may also be coherent, such as an array of lasers, and the spatial modulator can operate as a controllable holographic image quality of known type. In this case a directed hologram can be created that can be directed according to input data such as the tracking of one or more people viewing the display.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/004451 | 7/22/2013 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61673902 | Jul 2012 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13563117 | Jul 2012 | US |
| Child | 14414829 | US |
