Abstract:
An LED lamp for illuminating a surface under a flat angle in linear lighting applications such as cove lighting and wall washing is provided. It produces a uniform intensity distribution and a uniform color output throughout the beam pattern of the light beam produced by a multi-color LED light source. The lamp comprises a body of an extruded profile. The body comprises at least one section with a mirrored surface and at least a lens section which allows exiting of light from the body. At least one LED preferably having a LED lens is provided at the inner side of the body. This combination of optical systems results in an asymmetric beam pattern from the source.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a LED lamp and color mixing optics for illuminating a surface under a flat angle. The LED lamp produces a uniform intensity distribution and a uniform color output throughout the beam pattern of the light beam produced by a multi-color LED light source. 
     2. Description of Relevant Art 
     In linear lighting applications such as cove lighting and wall washing, it is desired to shape the beam of a lamp to achieve a uniform color and illuminance distribution on a target architecture surface, which may be a wall or a ceiling. As the illuminance incident on the target decreases as a function of the inverse of the light travelling distance (inverse-square law), the light intensity distribution from the lamp should be highly asymmetric. For example, a fluorescent pendant light which has a symmetric beam shape would illuminate the upper wall much brighter than the lower wall. 
     Color LED lamps should have an even intensity and color distribution over a broad range of radiation angles. As there is no single point LED source available, the radiation of multiple LED sources must be combined to form a multi-color light source. These multiple LED sources are placed offset to each other, so there is no common focal point. To obtain an even color distribution, color mixing is required. 
     Another important factor impacting the illumination uniformity is the setback distance, which is defined as the perpendicular distance between the luminaire aperture and the target surface. A small setback distance is usually preferred by lighting and architecture designers, but too short distance may reduce the uniformity, resulting in bright spots on the target plane. 
     U.S. Pat. No. 8,529,102 discloses a reflector system for a multi-color LED lamp providing color mixing. The system uses two reflective surfaces to redirect the light before it is emitted. 
     US Publication No. 2007/0171631 discloses LED cove lighting comprising a large and complex aluminum mirror system to obtain a uniform light distribution at a wall. 
     SUMMARY OF THE INVENTION 
     The embodiments are based on the object of making a LED lamp and a color mixing optic for color LED lamps which produces uniform intensity and color throughout the entire light beam when illuminating a surface under a flat angle. Furthermore, the optic should be simple, robust as well as easy and cost-effective to manufacture. The setback distance should be small compared to the length of the surface. Another embodiment is based on the object of making a color LED lamp comprising the color mixing optic. 
     In an embodiment, a lamp comprises a body which may further comprise a profile, preferably a hollow profile or an extruded profile. The body preferably comprises at least one section with a mirrored surface and at least a lens section which allows exiting of light from the body. At least one LED preferably having a LED lens is provided at the inner side of the body. This combination of optical systems results in an asymmetric beam pattern from the source. 
     At least one LED, preferably a plurality of LEDs are mounted on a LED mounting plane. It is mounted on a preferably planar mounting surface which preferably extends in a plane defined by the direction of extrusion. Preferably, a plurality of LEDs is aligned on a common center line, which preferably extends into the direction of extrusion. This mounting surface may comprise a printed circuit board or any other means for holding the at least one LED and preferably further electronic components. This embodiment relates to a color LED lamp and therefore requires multicolor LED emitters. These are preferably different LED chips combined to generate a plurality of visible colors. Herein, reference is made to a LED which means a plurality of LED chips for generating the different colors. Preferably, each LED is covered by a LED lens which preforms the beam pattern emitted by the LED and which further may protect the LED. 
     Close to the LED lens, the mirrored surface of the body has at least one paraboloidal section, preferably two paraboloidal sections. Preferably, at least one of the paraboloidal section has its focus line which is coincident with the LED center line. If a plurality of paraboloidal sections is provided, preferably at least two of these sections have the same focal length, and most preferably have the same focal line which is further preferably coincident with the LED center line. The paraboloidal sections deflect most of the light emitted by the at least one LED into a direction which is roughly parallel to the LED mounting plane and which exits the lamp through a first lens forming a first exit surface of the body. It is further preferred that the paraboloidal sections are slightly rotated around the focal line in a plane perpendicular to the direction of extrusion against each other. This results in a slightly different main beam direction of the lamp. 
     It is further preferred to have at least one arc-shaped reflector. Most preferably, there are three arc-shaped reflectors. These arc-shaped reflectors preferably are next to the at least one paraboloidal section. Preferably, they deflect a further part of the light through a second lens, under an angle which may be any flat angle up to a 90 degree angle to the mounting plane of the LED by means of the arc-shaped reflectors. Another part of the light is reflected towards the first lens. 
     For capturing residual light, a backside reflector may be provided at one side of the LED oriented towards the prime lens and set back from the mounting plane of the LED. 
     The embodiments described herein provide a better light distribution on a surface or wall with a reduced setback distance and provide an improved color mixing. The body is made of a robust profile and may be easily manufactured. It provides a fully enclosed housing which protects the LEDs and the inner optics from environmental influences. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, the invention will be described by way of example, without limitation of the general inventive concept, on examples of embodiment and with reference to the drawings. 
         FIG. 1  shows a sectional view of a first embodiment. 
         FIG. 2  shows a first embodiment of an LED with a lens. 
         FIG. 3  shows a further LED lens. 
         FIG. 4  shows ray traces of different rays. 
         FIG. 5  shows an extruded profile of the LED lamp. 
         FIG. 6  shows an LED lamp illuminating a wall. 
     
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIG. 1 , a sectional view of a first embodiment is shown. The LED lamp  10  has a body  11  which may be based on an extruded profile, preferably an extruded metal or plastic profile. Preferably, the extrusion direction is the y direction as indicated. An LED  41  is held at an LED mounting plane  81  which is parallel to a y-z-plane with the coordinates shown. Preferably, a plurality of LEDs is aligned on a common center line, which preferably extends into the y direction. This embodiment relates to a color LED lamp and therefore requires multicolor LED emitters, which when combined provide a multi-color LED light source. The multicolor LED emitters are preferably different LED chips configured to generate a plurality of visible colors, which combine to produce blended light. Herein, reference is made to an LED which means a plurality of LED chips for generating the different colors. The LED is covered by an LED lens  42  which will be shown later in full detail. Approximately opposite to the LED lens  42 , there is a first paraboloidal section  51  and a second paraboloidal section  52 . In this embodiment, both paraboloidal sections preferably have the same focal line which is at or at least close to the LED  41  center line. It is further preferred, if the paraboloidal sections are rotated slightly against each other, as will be shown later in detail. It may be possible to include further paraboloidal sections. There are further three arc-shaped reflectors  53 ,  54 , and  55  which are used to deflect the light from the LED through a second exit surface to the outside of the lamp. 
     Most of the light emitted by the LED is deflected by the paraboloidal sections. This light is radiated through a prime lens  56  defining a first exit surface. The prime lens has a lens body  61  and may have a Fresnel-lens like surface structure. The surface may have a plurality of slopes which define the light distribution at the output of the lamp. The light deflected by the arc-shaped reflectors  53 ,  54 , and  55  is guided through an outside lens  62  forming a second exit surface of the lamp. Finally, there is a backside reflector  63  which is reflecting light rays back to the interior of the lamp. 
     The LED base plane, the paraboloidal sections, the arc-shaped reflectors, the lens body, the outside lens, and the backside reflector enclose the inner volume of the lamp. They form an elongated body which may be closed at its end by others, which may only be protective covers which may also have a reflective inner surface. At least one or all of the reflective surfaces in the lamp may be total reflecting surfaces or may be mirrored surfaces (or other reflecting coated surface) or a combination thereof. 
     In  FIG. 2 , a first embodiment of an LED  91  together with a lens  92  is shown. Here, the lens  92  is a semi-sphere with the LED  91  located at the center. As the light rays propagate under a right angle from the lens to the outside, there is no refraction generating a Lambertian output. 
     In  FIG. 3 , a further LED lens is shown. In this embodiment, the lens  42  is a spherical dome or spherical cap, where the center  83  of the sphere is below the LED  41 . Therefore, the diameter  84  of the base of the cap is smaller than twice the radius  85  of the sphere. In this embodiment, the light is refracted when leaving the lens and is spread to the sides improving intermixing between multiple LED emitters reducing the bright spots created by discrete sources, which may be part of the LED  41 . In a preferred embodiment, the diameter of the bottom aperture may be 7.5 mm, while the radius of the sphere is 4.8 mm. 
     In  FIG. 4 , ray traces of different rays are shown. First rays  71  which are deflected by the first paraboloidal section  51  are deflected through the lens body  61  at a first light exit surface. Second rays  72  are reflected by a second paraboloidal section  52  under an angle to the first rays  71 , therefore spreading the light to a slightly different area of a surface to be illuminated. Preferably, both paraboloidal sections have their focus lines at the location of the LED center line. Most preferably, they are slightly rotated against each other. There may be further paraboloidal sections to further control the distribution of light. Third beams  73  are reflected by a first arc-shaped reflector  53 , mainly towards a backside reflector  63  which further reflects the light through the lens body  61 . Fourth rays  74  are reflected by a second arc-shaped reflector  54  mainly through an outside lens  62 . Similarly, there may be rays reflected by the first arc-shaped reflector  53  which also may propagate through the outside lens  62 . Generally, the arc-shaped reflectors  53 ,  54 , and  55  are reflecting parts of the light through the outside lens  62 , by means of the backside reflector  63  or directly through the lens body  61 , as shown by rays  75  and  76 . 
     In  FIG. 5 , an extruded profile of the LED lamp is shown. The lamp forms a hollow structure with reflecting side walls  51 ,  52 ,  53 ,  54 ,  55 , and  63 , and lenses  61 ,  62 . Along the length of the profile, there may be a plurality of LEDs and LED lenses  42  distant from each other. 
     In  FIG. 6 , an LED lamp  10  is shown illuminating a plane or wall  30 . The lamp is mounted distant from the wall under a setback distance  82 . There is a plurality of light rays  20  as described before, which are exiting the lamp  10  through the lens body  61 . There are further rays, like light rays  74  exiting the lamp body through outside lens  62 . 
     The embodiment shown herein provides a good color mixing of the light generated by a plurality of LED emitters, herein referred to as LED  41 , which are mounted under a lens  42 , and provides a uniform light distribution over a surface, like a wall. 
     It will be appreciated to those skilled in the art having the benefit of this disclosure that this invention is believed to provide optics for LED lighting with color mixing properties. Specifically, color mixing optics are disclosed herein for producing a uniform intensity distribution and a uniform color distribution throughout the entire beam pattern produced by a multi-color LED light source. Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims.