Abstract:
A lighting fixture includes a directional light source that produces a plurality of light rays. An optical module is coupled to the directional light source to focus the plurality of light rays into a beam of light rays to be output by the lighting fixture. The angular distribution of a majority of the beam relative to a vector normal to a ceiling on or near which the fixture is to be installed is in a range of 70 to 95 degrees. A blocking structure is used to block a direct view of the beam of light when the fixture is installed such that only indirect light is primarily visible from a viewer at least in or around a working plane substantially parallel to the ceiling.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. provisional patent application No. 61/393,801 filed Oct. 15, 2010. 
     
    
     FIELD OF THE INVENTION 
       [0002]    Embodiments of the invention relate to methods and apparatuses utilizing LED light sources however it is recognized that other directional sources could be used instead. Directional light sources are sources characterized by the ability of an optical system to groom the emitted light into a beam. For example a laser is a directional source. Another example is a waveguide that is coupled to a remote source. Yet another example of a LED light source that is used to make a beam is the arc lamp used in projectors. 
       BACKGROUND OF THE INVENTION 
       [0003]    Definitions 
         [0004]    CILF: Conventional Indirect Lighting Fixture as used in the prior art. 
         [0005]    Coefficient of Utilization: The ratio of the integrated light power at the working plane to the total light power emitted by the fixtures. 
         [0006]    IES: Illuminating Engineering Society. 
         [0007]    LED: Light Emitting Diode. 
         [0008]    Lumen: A photometric measure of light intensity. 
         [0009]    Luminous Intensity: Lumen density in a particular direction. 
         [0010]    OPDS: Optical Power Distribution System. 
         [0011]    PCB: Printed Circuit Board. 
         [0012]    Working plane: an imaginary plane at a specified distance from the floor (usually 28 inches) used as a reference to measure light intensity in a room. 
         [0013]    Lighting fixtures are composed of lighting source(s) and an “optical power distribution system” or OPDS. Until recently the majority of the light sources used for indoor lighting has been either incandescent or fluorescent light sources. Over the years a number of OPDS have been created that work well with those sources. Over the past 5 years the performance of LEDs has dramatically improved while simultaneously reducing the cost per lumen. It is therefore generally recognized that LED sources will eventually replace the older incumbent lighting sources. Most of the current LED product development is focused on providing light fixtures that use the same OPDS but use LED based lighting sources of essentially the same form factors as the incandescent and fluorescent light sources. This allows the customer to take advantage of the lower operating costs and increased lifetime of LED based light sources. 
         [0014]    What is needed is an improvement in indirect lighting performance using the special characteristics of LEDs or other small directional sources of low etendue, that allow the light fixture designer to more precisely direct a light beam to its target. For the most part indirect lighting is defined as lighting that comes from reflections from surfaces outside of the lighting fixture. The most common type of indirect lighting is from a hanging light fixture that has its optical power directed upwards towards the ceiling. Indirect lighting provides a superior quality of illumination because it is more uniform (less glare and hot spots) and is more isotropic (reduced shadows). It is generally acknowledged in the lighting industry that the reduction of hot spots and glare allows the user to achieve the same level of visual acuity at lower illumination levels. The key limitations of conventional indirect lighting are:
       1. It requires significant space between the indirect lighting fixture and the ceiling and therefore only works well with rooms with higher ceilings and/or vaulted ceilings.   2. The lighting efficiency (coefficient of utilization) is reduced by the blockage of the lighting fixture since the fixture is often times in plain view between the ceiling and the working plane.   3. It interrupts the continuity of the architecture of the room because it is very visible to the room occupant. Direct lighting has the advantage in this aspect because there are many recessed fixtures that are flush with the ceiling.       
 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0018]    Embodiments of the invention will be understood more fully from the detailed description given below and from the accompanying drawings of various embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments, but are for explanation and understanding only. 
           [0019]      FIG. 1  is a perspective view defining the normal vector to a planar surface. 
           [0020]      FIG. 2  is a perspective view of a room with a ceiling defining the normal vector to the ceiling of the room 
           [0021]      FIG. 3  (PRIOR ART) is a cross sectional view of a room showing the angular distribution of a PRIOR ART indirect light fixture 
           [0022]      FIG. 4  is a cross sectional view of a room showing the angular distribution of light from an indirect light fixture in accordance with an embodiment of the invention. 
           [0023]      FIG. 5  is a cross sectional view of a room showing the resultant reflected light from an indirect light fixture where the ceiling has specular reflective characteristics in accordance with an embodiment of the invention. 
           [0024]      FIG. 6  is a cross sectional view of a room showing the resultant reflected light from an indirect light fixture where the ceiling has diffuse reflective characteristics in accordance with an embodiment of the invention. 
           [0025]      FIG. 7  is a cross sectional side view  700  and a front view  705  of LED secondary optics subassembly and defines the angles of the optical power vectors emitted by that subassembly. 
           [0026]      FIG. 8  is a plot of the relative luminous intensity versus angle for a LED secondary optics subassembly with circularly symmetric emission. 
           [0027]      FIG. 9  shows plots of the relative luminous intensity versus angle for a LED secondary optics subassembly with elliptically symmetric emission. 
           [0028]      FIG. 10  is a cross sectional side view  1000  and a cross sectional front view  1050  or a LED secondary optics subassembly in a room illustrating the reference orientation of the LED secondary optics subassembly. 
           [0029]      FIG. 11  is a top view of a linear array of LED secondary optic subassemblies illustrating the resultant superposition of beams from individual secondary optic subassemblies in two cases: Case A  1100  where the individual beams are narrow and Case B  1150  where the individual beams are wide. 
           [0030]      FIG. 12  is a cross sectional side view of a room occupied by an observer illustrating the direct observation of stray emissions from a LED secondary optics subassembly. 
           [0031]      FIG. 13  is a cross sectional side view of a room occupied by an observer illustrating an embodiment that includes a blocking structure that prevents the direct observation of stray emissions from a LED secondary optics subassembly. 
           [0032]      FIG. 14  is a cross sectional view of an embodiment of the invention which has independent adjustments for orienting various elements of that embodiment. 
           [0033]      FIG. 15  is a cross sectional view of an embodiment of the invention which has a fixed horizontal blocking shelf and a LED secondary optics subassembly that rotates. 
           [0034]      FIG. 16  is a cross sectional view of an embodiment of the invention which has a blocking shelf and a LED secondary optics subassembly that rotate together. 
           [0035]      FIG. 17  is a cross sectional view of an embodiment of the invention which has a blocking shelf and a LED secondary optics subassembly that rotate together. 
           [0036]      FIG. 18  is a cross sectional view of an embodiment of the invention which has a blocking shelf and a LED secondary optics subassembly that rotate together. 
           [0037]      FIG. 19  is a cross sectional view of an embodiment of the invention which has a blocking shelf and a LED secondary optics subassembly that rotate together. The blocking shelf is further characterized by the addition of an internal reflective plate to assist in projecting light into the room. 
           [0038]      FIG. 20  is a cross sectional view of an embodiment of the invention which has a blocking shelf that includes an interior reflecting plate. 
           [0039]      FIG. 21  is a cross sectional view of an embodiment of the invention that shows additional features on the upper and lower blocking structures to reduce self-illumination. 
           [0040]      FIG. 22  is a top view of a room with a criss-cross arrangement of bi-directional linear array fixture in accordance with an embodiment of the invention. 
           [0041]      FIG. 23  is a perspective view of a uni-directional linear array fixture in accordance with an embodiment of the invention. 
           [0042]      FIG. 24  is a top view of a uni-directional linear array fixture in accordance with an embodiment of the invention. 
           [0043]      FIG. 25  is a cross sectional side view of a unidirectional linear array fixture in accordance with an embodiment of the invention. 
           [0044]      FIG. 26  is a top view of a bidirectional linear array fixture in accordance with an embodiment of the invention. 
           [0045]      FIG. 27  is a top view of a reduced width bidirectional linear array fixture in accordance with an embodiment of the invention. 
           [0046]      FIG. 28  is a top view of a curve linear array fixture in a circular configuration with no interior surface illumination in accordance with an embodiment of the invention. 
           [0047]      FIG. 29  is a top view of a curve linear array fixture in a semi-circular configuration in accordance with an embodiment of the invention. 
           [0048]      FIG. 30  is top view of a curve linear array in a circular configuration defining a cross section for  FIGS. 31 and 32  in accordance with an embodiment of the invention. 
           [0049]      FIG. 31  is the cross section side view defined in  FIG. 30  for the case of annular blocking shelf areas per LED secondary optics subassemblies in accordance with an embodiment of the invention. 
           [0050]      FIG. 32  is the cross section side view defined in  FIG. 30  for cross firing LED secondary optics subassemblies with blocking walls of annular blocking shelf areas per LED secondary optics subassemblies in accordance with an embodiment of the invention. 
           [0051]      FIG. 33  is a perspective view of a curve-linear array fixture with independent control of sub-arrays in accordance with an embodiment of the invention. 
           [0052]      FIG. 34  is a top view of a 8 foot by 16 foot rectangular lighting fixture utilizing bidirectional linear array fixtures and an integral interior reflecting surface in accordance with an embodiment of the invention. 
           [0053]      FIG. 35  is a perspective view of a multi-tier curve-linear array fixture in a circular configuration in accordance with an embodiment of the invention. 
           [0054]      FIG. 36  is a top view of a room with wall mounted unidirectional linear array fixtures in accordance with an embodiment of the invention. 
           [0055]      FIG. 37  is top view of a room utilizing a combination of types linear and curve-linear array fixtures in accordance with an embodiment of the invention. 
         SUMMARY OF THE INVENTION 
         [0056]    Embodiments of the invention relate to distributing light on a flat ceiling parallel to the floor, however it is recognized that other shaped ceilings may be used. A ceiling is not always a simple plane parallel to the floor. It may be at an off angle or it may be made of several segmented planes. Furthermore it may be a curved surface. The apparatuses and methods taught here are also applicable to these situations. 
           [0057]    Embodiments of the invention relate to “Optical Power Distribution Systems” (OPDS) which scatter light off the ceiling. It is possible to combine an embodiment of the invention with a conventional light fixture to yield a hybrid light fixture. 
           [0058]    There are three sets of objectives for an embodiment of the invention. The first set of objectives address standard indirect lighting fixtures. The second set of objectives address the known problems with conventional indirect lighting. A third set of objectives expand the capabilities and features of indirect lighting. 
           [0059]    The first set of objectives is:
       1. Prevent the room occupant from seeing the light sources (LEDs and associated optics) directly.   2. Produce a more uniform distribution of light on the working plane. Mathematically this objective translates into minimizing Max/Min ratio (the ratio of maximum footcandles to minimum footcandles in the working plane). In the ideal case the Max/Min ratio is 1.0, however in reality a Max/Min ratio of less than 2.0 is considered excellent. This is important since a proper lighting design must provide adequate lighting for all of the room occupants. Therefore the minimum light level (in an area that is of significant size) must be above a specified design threshold. The Illuminating Engineering Society, IES, sets those standards for various applications. From a strictly energy conscious point of view, any illumination levels that are significantly above the minimum level are wasteful. Therefore the uniform distribution of light is not only important from an aesthetic perspective, it is also important from an energy conservation perspective.   3. Extend the field of illumination from the fixture such that the spacing between fixtures is large (and still maintaining uniformity in terms of distribution of light). Reducing the amount of fixtures in a given space reduces capital equipment costs, installation costs and maintenance costs. Traditional lighting practices for large office spaces assume that the linear fixtures are hanging from ceiling as pendants and are arranged in parallel linear arrays. Typically there is a tradeoff between meeting objective #2 and meeting objective #3. For example imagine a room designed with linear arrays of florescent lighting at 10 foot spacing with a Max/Min ratio of 2.5. If the spacing between the fixtures is increased to 16 feet then the Max/Min ratio may increase to 3 or more. If the field illumination is large enough compared to the dimensions of the room then it is possible to light the room by using only wall mounted fixtures, i.e. without using any pendant lighting. This is particularly useful in situations where there is no ready access to a source of electricity above the ceiling; for example most modern hotels do not have a crawl space between the ceiling and the floor directly above it.       
 
           [0063]    The second set of objectives is:
       1. Reduce the space requirements. As mentioned earlier the conventional means of implementing indirect lighting requires a significant space between the fixture and the ceiling.   2. Improve the efficiency. As mentioned earlier in the conventional means of implementing indirect lighting the lighting fixture partially blocks the reflected light from the ceiling.       
 
           [0066]    The third set of objectives is:
       1. Provide a means for reducing or eliminating the self-illumination of the fixture such that the light fixture appears to be dark even when it is on.   2. Provide a means of altering the distribution of light to accommodate the changing requirements of the user and to accommodate physical changes of the lighting fixture due to aging, vibration, temperature that may result in unwanted changes in the lighting distribution pattern.   3. Provide a means for changing the intensity of light either uniformly or by zone to accommodate the changing requirements of the user.   4. Provide a means for changing the color of light either uniformly or by zone to accommodate the changing requirements of the user.   5. Provide a means for hiding and or camouflaging the light fixture entirely.       
 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0072]    For the purposes of differentiating between conventional, or prior art, indirect lighting OPDS s and the indirect OPDSs contemplated in embodiments of the invention, the following features of OPDS s are highlighted: (1) the angular distribution of light from the light fixtures relative to the ceiling, and (2) the means for obscuring or blocking the direct view of those light sources or any interior fixture surfaces with high brightness. 
         [0073]    Optical Angular Distribution 
         [0074]    The ceiling&#39;s normal vector is defined as the vector that is perpendicular to all lines tangent to the plane.  FIG. 1  illustrates the simplest case in which the ceiling surface is a plane  100  with a vector  105  normal to the surface of the plane. A planar surface is particularly important because most rooms  200  have a ceiling  205  which is a plane and an associated normal vector  210 , as shown in  FIG. 2 . Now consider  FIG. 3  showing the prior art where a conventional indirect light fixture  305  is hanging from the ceiling  315  in room  300  with a floor  320  and sidewalls  310 A and  310 B. Define θ as the angle between a given light ray from the light fixture and the normal vector  350 , where θ=0° when the normal vector and the light ray are parallel and in the same direction. The light rays from that fixture  305  intersect the plane of the ceiling  315  at various angles (e.g. θ 1   325 , θ 2   330 , θ 3   335 , θ 4   340 ) relative to the normal vector  350  of the ceiling. Conservatively speaking for conventional indirect lighting fixtures over 50% of the power incident on the ceiling has a value for θ such that θ&lt;60°.  FIG. 3  shows angles that are exemplary of this range where θ 1   325  is shown as 35°; θ 2   330  is shown as 20°; θ 3   335  is shown as 30°; and θ 4   340  is shown as 40°. 
         [0075]    Now consider a light fixture  420  in accordance with an embodiment of the invention, as shown in  FIG. 4 . It uses of a set of directional light sources, such as LED array  460 , whose optical output power is groomed into beams by OPDS&#39;s  455 A and  455 B directed towards the ceiling  405 . One of the salient features of a beam is the angular distribution of the light rays in those beams relative to the vector normal  450  to the ceiling, i.e. the distribution of the angles θ 1   425 , θ 2   430 , θ 3   435 , θ 4   440 , and θ 5   445  In one embodiment of the invention, the angular distribution of a beam is such that over 50% of the optical power emitted makes an angle θ with the normal vector  450  of the ceiling  405  such that 70°&lt;θ&lt;95°.  FIG. 4  shows angles that are exemplary of this range where θ 1   425  is shown as 90°; θ 2   430  is shown as 80°; θ 3   435  is shown as 75°; θ 4   440  is shown as 75°; and θ 5   445  is shown as 90°. It should be noted that while  FIG. 4  refers to an LED array as a directional light source, other types of light sources may also be used. 
         [0076]    For example, a laser is a directional light source. Another example is a waveguide that is coupled to a remote light source. Yet another example of a LED light source that is used to make a beam is the arc lamp used in projectors. An arc lamp, or arc light, is the general term for a class of lamps that produce light by an electric arc (also called a voltaic arc). The lamp consists of two electrodes, typically made of tungsten, which are separated by a gas. The type of lamp is often named by the gas contained in the bulb, including neon, argon, xenon, krypton, sodium, metal halide, and mercury. The common fluorescent lamp is actually a low-pressure mercury arc lamp. 
         [0077]    Most of the light will reflect from the ceiling, i.e. for θ such that 70°&lt;θ&lt;9 0 °. Optionally, in one embodiment, some portion of light may reflect off the top of the side walls. Consider the two embodiments for the light reflecting from the ceiling, as shown in  FIG. 5  and  FIG. 6 .  FIG. 5  shows the specular reflection embodiment where a room  500  has a ceiling  505  that is minor-like. In this embodiment an incident light ray  540  from the light fixture  520  will reflect off the ceiling  505  in a reflected light ray  545 , such that angle γ 1   550  is equal to angle γ 2   555 . In this embodiment the vertical component of the light is small. If the ceiling  605  acts as a perfect light scatterer then the reflected light is represented by the embodiment shown in  FIG. 6 . In this embodiment an incident light ray  635  from the light fixture  620  is reflected off the ceiling  605  into a diffuse set of reflected lights rays  640 ,  645 ,  650 ,  655  and  660 . This is diffuse reflection; a special case of which is lambertian reflection. In this embodiment, a significant portion of the resultant reflected rays have a significant vertical component. If the light incident upon the ceiling is uniformly distributed then the effect is to make the ceiling appear to be a uniform light source to the occupant of the room. Most ceilings in homes and offices today have considerable texture and therefore are more closely approximated by the embodiment illustrated in  FIG. 6 . 
         [0078]    Blocking Structures 
         [0079]    The LEDs and the LED secondary optics used to create the desired optical distribution pattern have significant secondary emissions, i.e. emissions outside the primary beam of light. The secondary optics is defined by an additional optics external to the LED assembly. It is termed secondary because the LED assembly may have its own embedded primary optics. The secondary optics input is generally coupled directly to the LED assembly output. Generally speaking at any interface where there is a change of direction of a light beam (either by reflection or by the refractive effect of changing of index of refraction in the transmission media) there is an opportunity to produce secondary emissions. Even in the exit of the primary beam from the secondary optics there is a portion of that optical power that is reflected back into the optics and subsequently re-emitted at angles outside of the primary beam. As a result the observer that is outside of the range of the primary beam can still see significant light being emitted by the LED secondary optics, often referred to and termed herein as stray emissions of light rays. It is therefore important that a blocking structure be used to block the direct view of the LEDs and its associated secondary optics. For CILFs the blocking is much less critical because the angle of the light distributions from the CILF is not close to the angle of view. However for embodiments of the invention the angular distribution of the primary beam, for example, from an LED assembly, can be within a few degrees of the viewing angle. 
         [0080]    A blocking structure may take many forms, according to an embodiment of the invention. The functions of a blocking structure are: (a) block direct view of the LEDs and/or secondary optics, (b) not significantly obstruct the primary beam from its target, and (c) in the case that the primary beam is obstructed then redirect that portion of the primary beam that was obstructed back to the ceiling in an angular direction within the angle of the unimpeded primary beam. One aspect of a blocking structure is a blocking shelf. 
         [0081]    Several aspects of the blocking structure in accordance with an embodiment of the invention are discussed below, including:
       1) The size of the minimum blocking shelf necessary to prevent direct view of the LEDs and their associated optics is proportional to the size of the secondary optics.   2) The size of the blocking shelf is a contributing factor to the size of the light fixture using a blocking shelf, in one embodiment of the invention.   3) The size of the blocking shelf is related to distance that light can be projected from the fixture. Fixtures with larger blocking structures can project light further into the room.   4) As rooms become larger the depth of the blocking shelf in some embodiments becomes larger until it reaches an asymptote, where the vertical displacement of the blocking structure equals the size of the secondary optics.       
 
       Embodiments of the Invention 
       [0086]    Embodiments of the invention implement a fully functional lighting system for a room or a set of rooms in a building. The entire system incorporates embodiments that are integrated into a light fixture design, and finally a room level solution integrates the light fixture functionality. Therefore the embodiments disclosed are vertically integrated into the final room lighting solution. 
         [0087]    Achieving the Desired Angular Distribution 
         [0088]    The optical output of an embodiment of the invention is ultimately the superposition of the individual beams from the LED+Optics combinations. For each LED there are beam shaping optics and beam directing mechanisms. In some embodiments the beam shaping optics and beam directing mechanisms are integrated. In some embodiments the beam shaping optics and beam directing mechanisms are shared by more than one LED. 
         [0089]    As a starting point first consider that the LEDs are generally mounted on a PCB (printed circuit board). The beam shaping optics for the LED are composed of three parts: the primary optics, the secondary optics, and fixture optical constraints. The fixture optical constraints are for the most part the interior surface of the blocking structure, discussed further below. Most of the popular high brightness (HB) LEDS sold today are actually sub-assemblies that include miniature optics to precondition the emissions from the LED and to physically protect the LED. These optics are sometimes referred to as the primary optics. For example, the Luxeon Rebel and Cree Xlamp products include a small lens. It should be noted that some LEDs do not include primary optics, for example Nichia&#39;s 157A series does not include primary optics. At the other extreme are companies that integrate all the required optics into the LED, e.g. Illumitex, and don&#39;t require a secondary optics. 
         [0090]    The choice of the secondary optics is a function of many factors including the LED array geometry, e.g. the number and the configuration of all the contributing LEDs and the room geometry. The secondary optics may be discrete, i.e. one secondary optic per LED, or multiple, i.e. one secondary optic structure serving multiple LEDs (for example a bar optics for a linear array of LEDs). Furthermore the secondary optics may be a custom solution or an off the shelf solution. Discrete secondary optics modules are readily available off the shelf from a number of vendors, e.g. Carclo, Ledil, Polymer Optics, and Dialight to name a few. Because off the shelf secondary optics are generally made to service several LED types, e.g. a Carclo secondary optics may be used with a Cree LED or Philips Lumiled LED, the performance will be inferior to a custom secondary optics solution. There are many parameters characterizing the performance of the secondary optics, e.g. angular distribution, throughput loss, and aperture size. As will be discussed below the aperture size is a consideration for embodiments of the invention because it is directly proportional to the size of the structure necessary to block the room occupant&#39;s view of the LEDs. The throughput loss is a consideration because it is part of the overall efficacy equation. A further consideration in connection with the beam shaping of the light emitted from the LED is the angular distribution. Some embodiments use secondary optics that have a circular symmetry or elliptical symmetry.  FIG. 7  illustrates a general secondary optics  725 . The direction of the optical power vector  730  is determined by two angles: (1) the angle, φ  735 , with the central axis  715  of the secondary optics  725 , and (2) the angle, α  740 , of the projection  745  of the optical power vector on the plane transverse  750  to the central axis  715  of the secondary optics  725  with the reference line  755  (typically a line of symmetry passing through the central axis). The secondary optics is considered circularly symmetric if the power level incident on a plane perpendicular to the central axis of the beam is independent of α. The lines in this plane perpendicular to the central axis of the beam representing a constant power are circular in shape. 
         [0091]    A typical angular distribution is shown in  FIG. 8 , having its peak power at φ=0 and its half power at φ=φ 3 dB    810 B and φ=−φ 3 dB    810 A. For a secondary optics that has an elliptical symmetry, the lines tracing out constant power levels on any plane intercepting the beam perpendicular to its central axis are elliptical in shape. The angular distribution is shown in  FIG. 9  which plots the Relative Luminous Intensity  905  as a function of φ  900 . There are two curves shown, i.e one curve  925  for power distribution as a function of φ  900  at α minor =angle of the minor axis of the ellipse, and one curve  920  for the power distribution as a function of φ  900  at α major =angle of the major axis of the ellipse. For convenience let&#39;s assume that α major =0 degrees and α minor =90 degrees. The elliptical shape is characterized by two 3 dB angles: (1) a 3 dB angle for the minor axis of the ellipse, φ 3 dB,minor    910 B and (2) a 3 dB angle for the major axis of the ellipse, φ 3 dB,major    915 B. 
         [0092]      FIG. 10  shows the reference orientation of the secondary optics relative to the room features, i.e. ceiling  1010  and floors, from two views: a) the side view  1000  of the near wall and b) the front view  1050  of the far wall. Furthermore the reference orientation, i.e. orientation without any tilt, is defined as follows: (1) the central axis  1015  of the LED secondary optics subassembly  1025  is parallel to the plane of the ceiling  1010 , (2) the minor axis  1065  of the elliptical beam  1055  is perpendicular to the ceiling  1010 , and (3) the major axis  1060  of the elliptical beam  1055  is parallel to the floor. 
         [0093]    The beams created by the LED secondary optics subassembly are then directed towards the ceiling by the fixture by tilting the LED secondary optics subassembly from its reference position to the ceiling of the room (the ceiling is assumed to be flat and parallel to the floor). 
         [0094]    The specifics regarding the mechanism used to orient the LED secondary optics subassembly and any additional beam shaping accomplished by the fixture optical constraints are a function of the particular fixture design (see the discussion below regarding Embodiments of Fixtures). The orientation mechanism is generally field adjustable to some extent to account for variances in room geometries and construction variances, according to an embodiment of the invention. 
         [0095]    Some embodiments of the invention use secondary optics that have an elliptical angular distribution where φ 3 dB,minor &lt;&lt;φ 3 dB,major . The reason becomes apparent if one considers a typical situation as illustrated in  FIG. 4 , in conjunction with  FIGS. 7 and 9 . Consider  FIG. 7  which shows the definition of angles that are used to describe the angular distribution. Furthermore assume that the LED/secondary optics assembly is directed such that most of the light being emitted by the assembly is incident on the ceiling. More specifically, with reference to the right hand side of the fixture in  FIG. 4 , let us assume that θ 4   440  is the angle for the closest intercept of the primary beam with the ceiling and that θ 5   445  is the angle of the farthest intercept of the primary beam with the ceiling. Furthermore let us assume that values for θ 4  and θ 5  respectively are 79° and 88° in one embodiment of the invention. If one further orients the angle of the central axis of the secondary optics such that it equally bisects the angle between θ 4  and θ 5  then the optical distribution of the LED/secondary optics assembly is constrained between −4.5° and +4.5°. If one assumes a reasonable power distribution where 80% or more of the power is captured in the range of −φ 3 dBm,minor &lt;φ&lt;φ 3 dB,minor , then one can use a LED secondary optics subassembly that has a φ 3 dB,minor  approximately equal to 4.5°. This is representative of some embodiments in that φ 3 dB,minor  is less than 5 degrees. On the other hand φ 3 dB,major  is typically chosen to be greater than 20 degrees. The primary reason for this is illustrated in  FIG. 11 . In case A the angular distribution of the beam from the LED/secondary optics array  1110  in the plane parallel to the ceiling is much smaller than in case B. As a result the optical power at point A  1105 , a distance x from the linear array, is only sourced by a single LED. However for case B  1150  consider point B  1155  at the same distance x from the linear array  1120 . In this case the optical power incident on the area around point B  1155  is contributed to by 5 LED/secondary optics beams. Choosing large angular distribution therefore will average out the variances in intensity and color of individual LEDs in the LED array. 
         [0096]    Managing Stray Emissions 
         [0097]    As shown in  FIG. 12  nearly all of the optical power from the LED-Lens assembly  1215  within the primary beam  1220 , where the primary beam is defined as light that exits the light source  1215 , passes through the fixture exit port and is incident on the ceiling  1200  and the upper portion of the far wall  1205 . However a much smaller amount of power is emitted outside of the primary beam  1220 , defined as stray emissions  1230 . This results, in part, from the scattering that occurs at the various optical interfaces within the LED-Lens assembly  1215 . These stray emissions can reach the eye of the observer  1210  either directly or by reflection off the light fixture. Because the LEDs have high luminous intensity, then the stray emissions are of significant magnitude. Therefore direct observation of the stray emissions creates significant glare and degrades the effectiveness of the indirect lighting. It is therefore desirable that direct observation of stray emissions be significantly reduced or entirely eliminated, in one embodiment of the invention. Additionally the illumination of the light fixture by the stray emissions should be greatly reduced in order to achieve the effect of producing indirect lighting in a room without revealing the source, in one embodiment. 
       Preventing Direct Observation of Stray Emissions 
       [0098]      FIG. 13  shows the blocking of the line of sight  1300  of the room occupant  1310  by a blocking structure  1340 . The aperture of the LED secondary optics assembly  1335  is blocked from the view of the observer  1310  by a shelf  1340 . The minimum depth  1360  of the shelf to completely block the view of the LED secondary optics  1335  is dependent on the relative orientation of the shelf  1340  with respect to the LED secondary optics  1335 . For the purposes of establishing equations relating the minimum shelf depth with room and fixture characteristics the following terms are defined in  FIG. 13 :
       h 1   1315  is the height of the room.   h 2   1320  is the height of the observer&#39;s eyes  1310 .   y 1   1325  is the drop from ceiling  1330  of the center of the LED secondary optics  1335 .   B 1   1305  is the angle of the line of sight  1300  with respect to horizontal  1370 .   D 2   1365  is the distance between the LED secondary optics  1335  and the far wall  1375 .   θcenter  1350  is the angle of the central axis  1345  of the LED secondary optics  1335  with the normal vector of the ceiling  1355 .       
 
         [0105]      FIG. 14  shows a fixture with the capability of independently adjusting the orientation of the LED  1465 —Secondary optics  1470 —shield  1445 —heat sink  1455 —printed circuit board  1450  sub-assembly, the orientation of the lower blocking structure  1415  and the orientation of the upper blocking structure  1405 . The orientation of the LED  1465 —Secondary optics  1470 —shield  1445 —heat sink  1455 —printed circuit board  1450  sub-assembly is accomplished by a pivot point A  1460  and a vertical adjustor  1440 . The orientation of the lower blocking structure  1415  is accomplished by pivot point C  1435  and vertical adjustor  1425 . The orientation of the upper blocking structure  1405  is accomplished by pivot point B  1430  and vertical adjustor  1420 . 
         [0106]    Consider further several different configurations of blocking structure and LED secondary optics orientations. 
         [0107]    One embodiment of the invention, referred to as Configuration  1 , is shown in  FIG. 15 . It has the following features, according to one embodiment of the invention: (a) the blocking shelf  1510  is fixed in a horizontal orientation, i.e. parallel to the ceiling  1530 , and (b) the LED secondary optics subassembly  1500  is oriented at an angle, θ center    1540 , with respect to the normal of the ceiling  1535 . The rotation angle of the LED secondary optics subassembly can be fixed at manufacturing or could be in part or in whole adjustable in the field by a rotating mechanism  1545 . In one embodiment of the invention, the minimum depth of the blocking shelf  1515  necessary to prevent the view of the LED secondary optics sub-assembly  1500  is given by the following formula: 
         [0000]        d   2   =w   a *(sin θ center /tan β 1 −cos θ center )
 
         [0000]    where, tan β 1 =(h 1 −h 2 −y 1 −(w a *sin θ center )/2)/d 1 
 
and furthermore the variables are associated with the following Figures:
 
         [0108]    From  FIG. 15  we have d 2   1515 , θ center   1540 , β 1    1525 , and w a    1505 . 
         [0109]    From  FIG. 13  we have h 1   1315 , h 2   1320 , d 1   1365 , and y 1   1325 . 
         [0110]    To get a better idea of the size of the shelf to use consider several cases shown in Table 1 below. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Case 1 
                 Case 2 
                 Case 3 
                 Case 4 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 wa 
                   
                 inches 
                 0.79 
                 0.79 
                 0.79 
                 0.79 
               
               
                 θ center   
                   
                 degrees 
                 85.00 
                 85.00 
                 85.00 
                 85.00 
               
               
                 θ center   
                   
                 radians 
                 1.48 
                 1.48 
                 1.48 
                 1.48 
               
               
                 h1 
                 height of room 
                 ft 
                 8.00 
                 8.00 
                 10.00 
                 10.00 
               
               
                 h2 
                 eye level 
                 ft 
                 6.00 
                 6.00 
                 6.00 
                 6.00 
               
               
                 d1 
                 width of room 
                 ft 
                 15.00 
                 20.00 
                 20.00 
                 50.00 
               
               
                 y1 
                 drop 
                 ft 
                 0.42 
                 0.42 
                 0.83 
                 0.83 
               
               
                 tan(β1) 
                   
                   
                 0.11 
                 0.08 
                 0.16 
                 0.06 
               
               
                 β 1   
                   
                 radians 
                 0.11 
                 0.08 
                 0.16 
                 0.06 
               
               
                 β 1   
                   
                 degrees 
                 6.03 
                 4.53 
                 9.00 
                 3.62 
               
               
                 d2 
                 min shelf 
                 inches 
                 7.36 
                 9.84 
                 4.89 
                 12.32 
               
               
                   
               
             
          
         
       
     
         [0111]    Under this configuration, the shelf depth becomes prohibitively large as the x/y footprint of the room increases, assuming all others factors remain constant. 
         [0112]    Another embodiment of the invention, referred to as Configuration  2 , is shown in  FIG. 16 . It has the following features: (a) the blocking shelf  1640  and the central axis of the LED secondary optics sub assembly  1600  are oriented at the same angle, θ center    1615 , with respect to the normal of the ceiling  1620  and (b) the blocking shelf  1640  is offset from the central axis  1645  of the LED secondary optics sub-assembly  1600  by a distance (w a /2+a 1 ), where w a    1605  is the size of the secondary optics aperture and a 1    1610  is the offset of the LED secondary optics sub-assembly  1600  from the blocking shelf  1640 , The minimum depth of the blocking shelf necessary to prevent the view of the LED secondary optics is given by the following formula: 
         [0000]        d   2 =( w   a   +a 1)/tan((π/2)−θ center +β 1 )
 
         [0000]    where, tan β 1 =(h 1 −h 2 −y 1 −w a /2)/d 1   
         [0113]    Table 2 shows the same cases as Table 1 but with the second configuration illustrated in  FIG. 16 . 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Case 1 
                 Case 2 
                 Case 3 
                 Case 4 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 wa 
                   
                 inches 
                 0.79 
                 0.79 
                 0.79 
                 0.79 
               
               
                 θ center   
                   
                 degrees 
                 85.00 
                 85.00 
                 85.00 
                 85.00 
               
               
                 θ center   
                   
                 radians 
                 1.48 
                 1.48 
                 1.48 
                 1.48 
               
               
                 A1 
                   
                 inches 
                 0.10 
                 0.10 
                 0.10 
                 0.10 
               
               
                 H1 
                 height of room 
                 ft 
                 8.00 
                 8.00 
                 10.00 
                 10.00 
               
               
                 H2 
                 eye level 
                 ft 
                 6.00 
                 6.00 
                 6.00 
                 6.00 
               
               
                 D1 
                 width of room 
                 ft 
                 15.00 
                 20.00 
                 20.00 
                 50.00 
               
               
                 Y1 
                 drop 
                 ft 
                 0.42 
                 0.42 
                 0.83 
                 0.83 
               
               
                 tan(β1) 
                   
                   
                 0.11 
                 0.08 
                 0.16 
                 0.06 
               
               
                 B 1   
                   
                 radians 
                 0.11 
                 0.08 
                 0.16 
                 0.06 
               
               
                 B 1   
                   
                 degrees 
                 6.03 
                 4.53 
                 9.00 
                 3.62 
               
               
                 D2 
                 min shelf 
                 inches 
                 4.55 
                 5.29 
                 3.56 
                 5.85 
               
               
                   
               
             
          
         
       
     
         [0114]    Table 2 illustrates that Configuration  2  has the advantage of reducing the minimum blocking shelf depth. 
         [0115]    It is recognized that Configuration  2  is representation of the general case where the angle Θ diff  between the central axis of the LED secondary optics subassembly and the blocking shelf is fixed. For configuration  2  θ diff  is zero. 
         [0116]    The embodiment of Configuration  2  also has a characteristic that further distinguishes it from the embodiment of Configuration  1 . If θ center  becomes large enough then the vertical projection of the blocking shelf on the ceiling normal vector will equal the vertical projection of the secondary optics and its offset a 1  on the ceiling normal vector. When this condition is satisfied then the depth of the blocking shelf is no longer dependent on the x/y footprint of the room. Mathematically this condition (that we shall call the infinite blocking condition for easy reference) occurs when the projection  1730  of the blocking shelf  1740  on the ceiling normal vector  1720  equals the projection of the secondary optics aperature w a  and offset a 1  on the ceiling normal vector  1720 , as illustrated in  FIG. 17 . This condition yields the following equation. 
         [0000]      sin θ center *( w   a   +a   1 )=cos θ center   *d   2  
 
         [0000]      or 
         [0000]      θ center   =a  tan( d   2 /( w   a   +a   1 ))
 
         [0000]    where d 2   1735  is the known depth of the blocking shelf  1740  and θ center    1715  is the variable to be adjusted to reach the infinite blocking condition, 
         [0117]    or equivalently solving for d 2 : 
         [0000]        d 2=( w   a   +a   1 )*tan θ center  
 
         [0000]    when θ center  is the variable to be adjusted to reach the infinite blocking condition. 
         [0118]    Table 3 shows several cases where d 2  is known and θ center  is the variable to be adjusted to reach the infinite blocking condition 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Case 1 
                 Case 2 
                 Case 3 
                 Case 4 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 wa 
                   
                 inches 
                 0.79 
                 0.79 
                 0.79 
                 0.79 
               
               
                 a1 
                   
                 inches 
                 0.10 
                 0.10 
                 0.10 
                 0.10 
               
               
                 d2 
                   
                 inches 
                 7.00 
                 6.00 
                 4.00 
                 3.50 
               
               
                 θ1 
                   
                 radians 
                 0.13 
                 0.15 
                 0.22 
                 0.25 
               
               
                   
                 complement of 
                   
                   
                   
                   
                   
               
               
                 θ1 
                 θcenter 
                 degrees 
                 7.22 
                 8.41 
                 12.51 
                 14.23 
               
               
                 θ center   
                   
                 radians 
                 1.44 
                 1.42 
                 1.35 
                 1.32 
               
               
                 θ center   
                   
                 degrees 
                 82.78 
                 81.59 
                 77.49 
                 75.77 
               
               
                   
               
             
          
         
       
     
         [0119]    If one designs a fixture to meet the infinite blocking condition then the fixture can be used in any room of any size, e.g. large office space, without exposing any of the LED secondary optics to the view of the room occupant. 
         [0120]    It is also noted that these equations show the tradeoff between fixture size, which is directly proportional to d 2 , and the horizontal distance from the fixture to where the light is incident on the ceiling, which is directly proportional to tan θ center . The objectives discussed above included (1) increase the spacing between fixtures and (2) decrease the size of the fixture. The objectives are contrary to each other. Having said that it is possible to find a compromise which is better than what is available with the CILFs. 
         [0121]    Let us define the horizontal distance from the LED secondary optics sub-assembly  1800  to the intercept of the central axis  1850  with the ceiling  1840  as X pen ,  1845  as shown in  FIG. 18 . 
         [0000]        X   pen   =y   1 *tan θ center  
 
       Where, 
       [0122]    y 1   1835  is the distance from the center of the LED secondary optics sub-assembly  1800  to the ceiling  1825 . 
         [0123]    θ center    1830  is the angle between the ceiling&#39;s normal vector  1825  and the central axis of the LED secondary optics sub-assembly  1850 . 
         [0124]    Table 4 below shows the value of X pen  (in feet) as a function of θ center  and y 1    
         [0000]    
       
         
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                   
                 y 1  (inches) 
               
             
          
           
               
                   
                 3 
                 5 
                 6 
                 7 
                 8 
                 10 
                 11 
                 13 
                 15 
                 17 
                 19 
                 22 
               
               
                   
               
             
          
           
               
                 θ center   
                 87 
                 4.8 
                 8.0 
                 9.5 
                 11.1 
                 12.7 
                 15.9 
                 17.5 
                 20.7 
                 23.9 
                 27.0 
                 30.2 
                 35.0 
               
               
                   
                 86 
                 3.6 
                 6.0 
                 7.2 
                 8.3 
                 9.5 
                 11.9 
                 13.1 
                 15.5 
                 17.9 
                 20.3 
                 22.6 
                 26.2 
               
               
                   
                 85 
                 2.9 
                 4.8 
                 5.7 
                 6.7 
                 7.6 
                 9.5 
                 10.5 
                 12.4 
                 14.3 
                 16.2 
                 18.1 
                 21.0 
               
               
                   
                 84 
                 2.4 
                 4.0 
                 4.8 
                 5.6 
                 6.3 
                 7.9 
                 8.7 
                 10.3 
                 11.9 
                 13.5 
                 15.1 
                 17.4 
               
               
                   
                 83 
                 2.0 
                 3.4 
                 4.1 
                 4.8 
                 5.4 
                 6.8 
                 7.5 
                 8.8 
                 10.2 
                 11.5 
                 12.9 
                 14.9 
               
               
                   
                 82 
                 1.8 
                 3.0 
                 3.6 
                 4.2 
                 4.7 
                 5.9 
                 6.5 
                 7.7 
                 8.9 
                 10.1 
                 11.3 
                 13.0 
               
               
                   
                 81 
                 1.6 
                 2.6 
                 3.2 
                 3.7 
                 4.2 
                 5.3 
                 5.8 
                 6.8 
                 7.9 
                 8.9 
                 10.0 
                 11.6 
               
               
                   
                 80 
                 1.4 
                 2.4 
                 2.8 
                 3.3 
                 3.8 
                 4.7 
                 5.2 
                 6.1 
                 7.1 
                 8.0 
                 9.0 
                 10.4 
               
               
                   
                 79 
                 1.3 
                 2.1 
                 2.6 
                 3.0 
                 3.4 
                 4.3 
                 4.7 
                 5.6 
                 6.4 
                 7.3 
                 8.1 
                 9.4 
               
               
                   
                 78 
                 1.2 
                 2.0 
                 2.4 
                 2.7 
                 3.1 
                 3.9 
                 4.3 
                 5.1 
                 5.9 
                 6.7 
                 7.4 
                 8.6 
               
               
                   
                 77 
                 1.1 
                 1.8 
                 2.2 
                 2.5 
                 2.9 
                 3.6 
                 4.0 
                 4.7 
                 5.4 
                 6.1 
                 6.9 
                 7.9 
               
               
                   
               
             
          
         
       
     
         [0125]    In either the embodiment of configuration  1  (illustrated in  FIG. 15 ) or the embodiment of configuration  2  (illustrated in  FIG. 17 ) part of the optical power from the secondary optics makes contact with the interior of the blocking shelf. The percentage of the power that is intercepted by the interior surface of the blocking shelf increases as a 1  decreases and d 2  increases. However most of this light is recovered if the interior surface of the blocking shelf redirects the light back towards the ceiling. The reflected light is directed farther away from the fixture if the interior surface is specular (mirror-like) rather than diffuse. Modifications can be made to the interior surface of the blocking shelf such that the reflected light from the interior surface of the blocking shelf will be cast farther away from the fixture. Just as it is important to achieve a large X pen    1845  for non-reflected light in  FIG. 18  it is important that the reflected light achieve a large X pen ,reflected  1915 , as shown in  FIG. 19  (approaching the value of X pen ). X pen ,reflected  1915  is the horizontal distance from the LED secondary optics subassembly  1905  to the intercept of the reflected light ray  1920  with the ceiling  1910 . The reflected light ray  1920  is the result of the reflection of an incident light ray  1925  from the LED secondary optics subassembly  1905  reflecting off the interior surface of the blocking shelf  1940 . The reflection is specular in that the incident angle  1935  is equal to the reflected angle  1930 . It is recognized that in some cases that visual appearance of the projection of light on the ceiling may have artifacts (discontinuities in brightness) that can be filled by making some portion of the reflected light from the inner surface of the blocking shelf diffuse. 
         [0126]    Any such embodiments that redirect intercepted light should be below the line of sight, or in the case of very large rooms below the horizontal line intercepting the highest edge of the blocking shelf. Consider  FIG. 20  showing an embodiment where an internal reflection plate  2045  has been added to the blocking shelf  2040 . A representative light ray  2025  from the LED secondary optics subassembly  2005  is incident on the internal reflection plate  2045  at an angle  2035 . The resulting reflected light ray  2020  intercepts the ceiling  2010  at a horizontal distance  2015 . Note that X pen ,reflected  2015  in  FIG. 20  is larger than X pen ,reflected  1915  in  FIG. 19 . 
         [0127]    In some cases it is advantageous to change the shape of the lower blocking shelf  2110  such that it has a lip  2115  as shown in the embodiments illustrated in  FIG. 21 . Likewise there are cases where the shape of the upper blocking shelf  2125  advantageously should include a lip  2120 . This gives the primary beam a sharper edge to it (i.e. the projected intensity changes more abruptly, rather than a gradual fade). Self illumination of the fixture can be reduced if the upper blocking shelf  2125  has a curved contour. 
       Reducing Self Illumination of the Light Fixture by Stray Emissions 
       [0128]    One of the objectives of an embodiment of the invention is to provide indirect lighting in a room while simultaneously not revealing the source of that indirect lighting. To that point it is important to reduce self illumination of the light fixture caused by stray emissions. This may be done in two parts, according to an embodiment of the invention: 
         [0129]    1) First, a chamber is constructed which allows only the front face of the LED Lens assembly to be visible, as shown as chamber  1445  in  FIG. 14  and as chamber  2130   FIG. 21 . Most of the stray emissions from the sides and back of the LED and the secondary optics are trapped in this chamber. The chamber is formed from the combination of the printed circuit board  1450  and the shields  1445  as shown in  FIG. 14 . In some embodiments the secondary optics lens holders  1470  provide a sufficient chamber. Furthermore the interior walls of this chamber be constructed of light absorbing material and exhibit only smooth curved contours, according to one embodiment, since sharp edges will cause additional scattering which could be externally visible. 
         [0130]    2) The exit chamber of the light fixture, chamber  2 , is defined by the volume delimited by the exit port  1475  of chamber  1 , exit port  1410  of the fixture, and the upper blocking structure  1405  and lower blocking structure  1415 . The interior of the light fixture consists of dark light absorbing material, again with no sharp edges, in one embodiment. The stray light from the front face of the LED secondary optics assembly is therefore contained in chamber  2 . 
         [0131]    Color Control 
         [0132]    Color management of “white” light is an issue to consider for lighting in general. Today, LED fixture consumers are forced to choose between various types of white light, e.g. cool-white (5000° K. to 10000° K.), neutral-white (4000° K.), and warm-white (3000° K.). Note that the color temperature of a light source is the temperature of an ideal black body radiator that radiates light of comparable hue to that light source. Warm-white has a better color-rendering-index and is preferred in most residential settings. Cool-white is used in the office because it creates an environment that is believed to result in higher level of energy of its occupants. In many cases it would be preferable to have a lighting system that could change to accommodate the varying needs of the room occupant by effectively changing its color temperature. This is possible by using several colors of LEDs, e.g. red, green, and blue LEDs, and mixing the appropriate relative intensities. One of the primary difficulties in implementing this approach is the rainbow effect along the edges of the illumination patterns, i.e. there is not sufficient color mixing to achieve a uniform hue of white. 
         [0133]    Three characteristics of embodiments of the invention disclosed herein make color mixing very effective:
       (1) the use of elliptical secondary optics results in a large number of LEDs contributing power at any given point on the ceiling,   (2) the upper blocking structure  1405  and lower blocking structure  1415  shown in the embodiment of  FIG. 14  produce a sharper edge to illumination patterns on the ceiling and the upper part of the walls, thereby reducing the instance of gradually fading from bright to dim. It is known that each color will have a slightly different fade angle due to the wavelength dependence of the optics, and therefore if such a gradual fade is allowed the color mix will change along the fade regions.       
 
         [0136]    (3) the scattering phenomenon that is the origin of the indirect light is wavelength independent. Furthermore color cameras with RGB filters may be used to achieve a closed loop control system. This allows one to maintain the hue of the white light over varying temperature and the lifetime of the system. Note that such feedback control also requires addressable control of LEDs or LED groups, as discussed later. 
         [0137]    Thermal Management 
         [0138]    LED lifetime and performance is a function of the junction temperature of the LED. As the temperature increases, the lifetime and the optical output power (for a fixed current) both decrease. One of the biggest problems facing the LED industry today is the managing of the temperature for bulb replacement parts, e.g. using LEDs to replace incandescent bulbs. The root cause of the problem is that there is inadequate heat sinking available for bulb replacement applications. On the other hand a light fixture in accordance with an embodiment of the invention as described herein has easy access to heat sinking elements. Consider the heat sink  1455  in  FIG. 14 . Also consider the heat sink  2520  in  FIG. 25 . Note that in  FIG. 25  the heat sink  2520  is an integral part of the subassembly that rotates together with the PCB  2525 , LEDs  2540 , secondary optics  2530  and lower blocking shelf  2505 . In  FIG. 14  the heat sink rotates around pivot point  1460  as part of the subassembly that also contains the PCB  1450 , LED  1465 , and the secondary optics  1470 . Therefore in both  FIG. 14  and  FIG. 25  the heat sink is directly attached to the PCB that carries the LEDs. This has the distinct advantage of keeping the thermal resistance low. The combination of large easily accessible heat sinks and the low power density is ideal for keeping the LED temperature low. 
         [0139]    Common to most of the light fixture embodiments discussed herein is securing the LED PCB assembly (PCBA) directly to a large heat sink. For the case in which the fixture provides a means for adjusting the angle of the exit beam with the ceiling, the apparatus that aims the LED/secondary optics at the ceiling should not interfere with the primary heat path. In one embodiment, the heat sink is fixed directly to the PCBA and both are rotated together. 
         [0140]    System Control 
         [0141]    Control of a White LED System 
         [0142]    A lighting system consists of multiple fixtures in a room. Each fixture can be independently addressed and controlled, in one embodiment. Within each fixture the LEDs may be grouped. Consider the embodiment  FIG. 23  which shows a fixture  2300  with with 16 LEDs separated into 2 groups: group A  2310  and group B  2320 . Each group has eight LEDs. Each group within a fixture may be addressed. A group may consist of only one LED. The control allows one to set the LED drive current for each group. This can be used to control the lux levels at various parts of the room. Consider  FIG. 22  which shows a large room illuminated by a crisscross configuration of linear unidirectional wall mount fixtures ( 2205 ,  2212 ,  2220  and  2225 ) and linear bidirectional pendant fixtures ( 2206 ,  2207 ,  2208 ,  2209 ,  2210 ,  2211 ,  2221 ,  2222 ,  2223 , and  2224 ). The room is partitioned into 5 rows ( 2230 ,  2231 ,  2232 ,  2233  and  2234 ) and seven columns ( 2240 ,  2241 ,  2242 ,  2243 ,  2244 ,  2245 , and  2246 ) For example it is possible to light only a single cubicle (e.g. cubicle at row  2232 , column  2242 ) in the embodiment of the very large configuration shown in  FIG. 22 . 
         [0143]    An example of the control of a curve-linear fixture  3300  is shown in the embodiment of  FIG. 33 , where the LED arrays are divided into three individually addressable groups, i.e. group A  3310 , group B  3320  and group C  3330 . The control may be centralized or distributed. An example of a centralized control would be a web based control that could be accessed through a secure password. An example of distributed control would be hardwired switches or dimmers in the room. 
       Control of Correlated Color Temperature of a White LED System 
       [0144]    In much the same manner as the control of white LED systems, groups of LEDs are sub-divided into color sub-groups, e.g. red, blue, green, etc. An interesting special case is the control of the color of the white light. Instead of the PCBA having different primary color LEDs the PCBAs are populated with intermixed LEDs of different CCTs (correlated color temperatures). For example suppose a PCBA has ten LEDs. In one embodiment, the even number LEDs could be at a 2700° K. and the odd number LEDs could be at a CCT of 4000° K. The even number LEDs are wired together in series number  1  and the odd number LEDs are wired together in series number  2 . Series number  1  uses current driver A while series number  2  uses current driver B. If the secondary optics are elliptical then there will be two levels of mixing. The first level of mixing occurs because of the overlap of elliptical beams as shown in  FIG. 11 . The second level of mixing occurs because of the diffuse scattering at the ceiling. Therefore the resultant light at the working plane, usually defined as 28″ from the floor, has undergone two levels of mixing. It should be noted that the two levels of mixing also facilitates the mixing of colors, and variances in white LEDs (whether by design or intentional as in the above example), 
         [0145]    Embodiments of Light Fixtures and their Application in Indoor Lighting 
         [0146]    There are many types of light fixtures that can be constructed according to the embodiments of the invention disclosed herein. The fixture embodiments disclosed in this section are representative of fixtures that can be constructed based on those embodiments. 
         [0147]    So far a blocking structure for a single LED has been described. However when multiple LEDs are combined into a light fixture the block structure should be suitable for all the LEDs, in one embodiment. Two lighting fixtures discussed here are linear array fixtures and curve-linear array fixtures. For linear array fixtures the LEDs are arranged in a straight line. For curve-linear array fixtures the LEDs are arranged on a curve that is substantially coplanar. Consider that the cross section, for either a linear array or a curve-linear array, formed by a plane passing through the center axis of any LED/secondary optics in the array and perpendicular to the ceiling, should be the same as for the single element embodiment discussed above. Therefore the various blocking structures discussed for a single LED embodiment are applicable to the linear and curve-linear array embodiments. 
         [0148]    Unidirectional Linear Array Fixture 
         [0149]    Let us assume the array fixture is linear. Consider the fixture  2400  in  FIG. 24 . Note that all LED secondary optics subassemblies  2430 , in either group A  2410  or group B  2420  are oriented in the same direction. In this embodiment, the blocking shelf is a straight planar structure  2440 . 
         [0150]    Additional details of the embodiment are shown in  FIG. 25 . Note that the PCB  2525  housing the LEDs  2540  and the secondary optics  2530  are mounted to a heat sink  2520 . The heat sink  2520  should be a material with a high thermal conductivity, in one embodiment. The heat sink  2520  should also be thick. The combination of high conductivity and thickness allows the heat generated from the LEDs  2540  to be spread over a larger area which in turn aids in the passive convective cooling of the fixture  2500 . Also note that the subassembly composed of the LEDs  2540 , secondary optics  2530 , heat sink  2520 , and blocking shelf  2505  rotate together relative to the external frame  2510 , in one embodiment. The rotation (or tilt) is accomplished by the hinge  2550  in combination with an adjustable spacer  2515  between the frame  2510  and the sub-assembly, in one embodiment. The frame  2510  provides a fixed structure presented to the observer independent of the rotation angle. Also note that there is an overlap between the downward lip  2560  of the blocking shelf  2505  and the upward lip  2570  of the frame  2510 . 
         [0151]    Unidirectional linear array fixtures are typically wall mounted as shown in  FIG. 22 ,  FIG. 36  and  FIG. 37 . In the case of a remodel or a new build the unidirectional linear array fixtures may be recessed into the wall. This embodiment provides significant, indeed, complete, reduction of observable fixture footprint. 
         [0152]    Bidirectional Linear Array Fixture 
         [0153]    There are a number of embodiments for a bidirectional linear array fixture. One embodiment of a bidirectional linear fixture  2600  comprises two unidirectional linear array fixtures positioned back-to-back, i.e.  2610  and  2620 , as shown in  FIG. 26 . The effective width  2630  is then twice the width of a uni-directional linear array fixture. 
         [0154]    Another embodiment is shown in  FIG. 27 . The effective width  2740  of the fixture  2700  is reduced by ½, relative to  FIG. 26 , by alternating the directions of the uni-directional linear array subassemblies. Uni-directional linear array subassemblies  2705 ,  2710 , and  2715  are all point in the same direction, as projected into the horizontal plane. The uni-directional linear array subassemblies  2720  and  2730  point in the opposite direction, as projected into the horizontal plane. In another embodiment, if one does not alternate directions of the LED/secondary optics but instead creates a direct cross firing situation then efficiency of the fixture decreases because the source beams may intercept part of the structure of the opposing source. One embodiment that allows for a higher density of opposing bidirectional sources employs a second vertical tier. Furthermore any given side of the fixture would alternate between tier  1  and tier  2  to make a more homogenous presentation of the light on the ceiling. Multiple vertical tiers can also be useful if additional optical power is required for the application. Bi-directional linear array fixtures may find utility as pendants in large rooms as shown in the embodiment of  FIG. 22 . 
         [0155]    Curve-Linear Array Fixtures 
         [0156]      FIG. 28  and  FIG. 29  show embodiments of curve-linear array fixtures.  FIG. 28  shows an embodiment of a fixture  2800  with a circular curve-linear array of LED secondary optics subassemblies  2810 . The blocking shelf  2820  is a coplanar annular ring.  FIG. 29  shows an embodiment of a fixture  2900  with a semi-circular curve-linear array of LED secondary optics subassemblies  2910 . The blocking shelf  2920  is a coplanar annular half-ring. These curve-linear embodiments find application, for example, as central fixtures  3725  and corner fixtures ( 3705 ,  3710 ,  3715 , and  3720 ) as shown in the room  3700  in  FIG. 37 . 
         [0157]    Alternative embodiments for blocking shelves for curve-linear array fixtures are described with reference to the cross section illustrated in  FIG. 30 .  FIG. 30  shows a fixture  3000  with a circular array of LED secondary optics subassemblies  3010  surrounded by an annular blocking shelf  3020  with a cross section notation  3025 . The cross section detailed in  FIG. 31  employs a blocking shelf construction that is similar to that disclosed for linear array embodiments.  FIG. 31  shows a fixture  3100  with LED secondary optic subassemblies  3105  and  3110  point in opposite directions, having separate blocking shelf areas  3115  and  3120  respectively. This configuration has a diameter  3125 . It is possible to achieve a smaller diameter by modifying the embodiment shown in  FIG. 32 . The modified fixture  3200  has blocking walls  3215  and  3220  associated with LED secondary optics subassemblies  3105  and  3110 . This will however reduce the lighting efficiency of the fixture. As discussed earlier it is possible to use a second tier of 
         [0158]    LED/secondary optics to resolve this problem and to use the same techniques of alternating between tier  1  and tier  2  to make a more homogenous presentation of light. 
         [0159]    Fixtures with Integrated Reflecting Surfaces 
         [0160]    The embodiments described thus far have used the ceiling as the surface to scatter light into the room. Consider that for some embodiments it may be advantageous to include a surface which is part of the fixture itself from which to reflect light. One embodiment comprises a rectangular configuration of bi-directional linear array fixtures ( 3410 ,  3415 ,  3420 , and  3425 ) as shown in the embodiment of  FIG. 34 . The advantage of this embodiment is that the interior reflecting material  3430  may be chosen to have the optimum reflection characteristics. An alternate embodiment of the configuration shown in  FIG. 34  uses fixtures that are all uni-directional in the direction pointing inwards to the interior surface. This fixture is similar to a traditional 2×4 troffer with the noteworthy exception that it is 16 times its area. An embodiment of this type of lighting fixture could be useful for large conference rooms. 
         [0161]    This same embodiment could be used to light the interior of the inner circle illustrated in  FIG. 28 , for example, by adding a second tier of LEDs/secondary optics  3500  pointing inwards, as shown in  FIG. 35 . 
         [0162]    Multi-Tier Curve Linear and Linear Array Fixtures 
         [0163]    As mentioned earlier it is sometimes advantageous to use multiple tiers of curve-linear or linear arrays to achieve more efficient lighting, according to one embodiment. Another embodiment involves multi-tier unidirectional linear array fixtures in large rooms in the configuration shown in  FIG. 36 . In one embodiment, if sufficient optical power is not possible from a single tier of LEDs, a second tier may be utilized. The tiers may or may not have the same angular direction.