Abstract:
Lighting louvers formed by transverse and longitudinal blades improve the performance of indirect ambient light luminaires by increasing light output, widening the output of the luminaire&#39;s maximum intensity light, or both. These lighting louvers include at least one of the following features: non-symmetrically shaped apertures, wider apertures over (or under) the luminaire&#39;s lamp(s), longitudinal blades of shorter height nearest the lamps, and longitudinal blades having differently curved longitudinal sides. Each of these features contributes to improved luminaire performance.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to luminaire louvers. More particularly, this invention relates to louvers that are sized, shaped, and arranged to improve the performance of luminaires.  
         [0002]     Luminaires (i.e., lighting units) can be used to provide indirect ambient lighting for interior spaces by directing some or all of their lighting to overhead surfaces. These types of luminaires are widely used in commercial installations where diffuse reflected light is desirable. They are especially common in office spaces, where such lighting is preferred for tasks involving video display terminals.  
         [0003]     Luminaires for ambient lighting are commonly suspended from ceilings. They usually have housings that conceal or otherwise shield their lamp(s) from direct view, while directing light upwards through apertures in the top of the luminaire. To minimize glare and maximize visual comfort, these luminaires provide as even a distribution of light (i.e., no bright spots) over as wide an area as possible. Such uniformity of light can be economically attained by using luminaires that (1) are suspended as far as possible from the surface to be illuminated and (2) emit their maximum intensity light at low upward angles. Coincidently, increased setback and wide light distribution also advantageously result in the fewest number of luminaires and the lowest power density (watts per square foot).  
         [0004]     However, suspension lengths are often limited, for example, by low ceiling heights, headroom issues, and the general notion that suspended lighting adds clutter to interior spaces. Even in known luminaires with relatively wide light spread distributions, limited suspension lengths often result in undesirable ceiling brightness and poor ceiling uniformity. In such cases, ceiling uniformity is especially compromised when luminaires are widely spaced to lower energy costs. Undesirable ceiling brightness and poor ceiling uniformity can cause reflected glare on display screens, increasing visual fatigue and reducing worker productivity.  
         [0005]     Luminaires for ambient lighting also are commonly mounted to furniture systems and low office partitions. Mounting heights for such luminaires typically range from about 48″ above the floor to about 65″ above the floor. These luminaires advantageously eliminate overhead lighting and potentially create a visually clean, uncluttered, and spacious-appearing interior environment. Moreover, these luminaires may also have bottom apertures that provide local supplementary direct lighting for office tasks. This eliminates the need for auxiliary task lights and further reduces energy use. Because these luminaires are generally mounted farther from ceilings than suspended luminaires, they potentially create more diffuse ambient light characterized by lower ceiling luminances, greater uniformity of ceiling brightness, and greater visual comfort.  
         [0006]     However, such furniture/partition mounted luminaires (i.e., indirect luminaires mounted below standing eye height) often have a housing with a large height profile to shield their lamps from direct view. Large height profiles can adversely affect the aesthetic appearance of an interior environment and can also adversely impact workstation functionality. For example, a panel-mounted luminaire with a large height profile may prevent a video display terminal from being positioned at the most desirable viewing location.  
         [0007]     While some reduction in height profile is possible with shielding devices (e.g., baffle or louver assemblies, described in detail below), shielding devices can also adversely affect the performance of a luminaire and thus diminish the advantages furniture/partition mounted luminaires have over luminaires suspended from ceilings.  
         [0008]     Luminaire performance for ambient light applications is determined by luminaire efficiency and the maximum intensity angle. Luminaire efficiency is the percentage of light generated by the luminaire&#39;s lamp(s) that is emitted from the luminaire; the closer to 100%, the higher the efficiency. The maximum intensity angle is the angle at which the maximum intensity light is emitted from the luminaire; the lower the angle, the wider the light distribution. Higher performance results from either higher efficiency, lower maximum intensity angle, or preferably both.  
         [0009]     Effective shielding devices can contribute to performance by preventing luminaire lamp(s) from being directly viewed while advantageously directing lamp output at low angles that minimize glare (i.e., at angles near but not at or below the viewing angle). However, as mentioned above, shielding devices can also detract from luminaire performance.  
         [0010]     For indirect luminaires employing linear type fluorescent lamps (e.g., 1″ diameter T8 or ⅝″ diameter T5 lamps) or long compact (twin-tube) fluorescent lamps, shielding is often performed by a baffle or louver assembly placed above the lamp(s) in much the same manner as a direct or downlight luminaire is fitted with a baffle or louver assembly below its lamp(s). Typically, such baffles or louvers are made of specular or semi-specular metal or metalized plastic fashioned to advantageously redirect light rays to prevent glare.  
         [0011]     Baffle assemblies typically have vertical blades arranged transversely (crosswise) to the lamp length. These vertical blades extend between two side members arranged parallel to the length of the lamp. Multiple vertical blades are arranged along the lamp length between the side members to form a series of apertures through which lamp light passes. The spacing of the blades combined with their height and the angle of light reflecting off their surfaces determine the longitudinal shielding angle of the luminaire. Similarly, the distance between the baffle side members, the angle of light reflecting off their surfaces, and the vertical distance at which the lamp is positioned below the top of the baffle sides determine the lateral or transverse shielding angle of the luminaire.  
         [0012]     A significant disadvantage of baffle assemblies involves the transverse shielding angle, transverse aperture width, and luminaire height profile. For a given lamp type, indirect luminaires with wide baffle assemblies, which advantageously result in greater overall efficiency with wider light distributions and greater light intensity at lower vertical angles, require the lamp to be located far below the aperture in order to have acceptable lateral shielding. This results in luminaires that are undesirably bulky with noticeably large height profiles, which can compromise the appearance of a space and limit workstation functionality.  
         [0013]     Louver assemblies generally combine a series of transverse (baffle) blades with longitudinal blades positioned between the side members and parallel to the lamp length. (As used herein, “transverse blade” and “cross blade” mean the same thing and are interchangeable.) These transverse and longitudinal blades create an array of multiple, usually rectangular, apertures through which lamp light passes. The result is an assembly wherein the spacing of the transverse and longitudinal blades, their respective heights, and the angle of light reflecting off their surfaces determine the longitudinal and transverse shielding angles of the luminaire.  
         [0014]     Generally, the vertical position of the lamp from the louver assembly has little to no effect on the shielding angle. Thus, luminaire height profile can be advantageously reduced to little more than the lamp diameter and louver height. To the extent that reduced louver blade spacings allow for reduced louver height without compromising the shielding angle, very low profile luminaires can be advantageously constructed.  
         [0015]     Uniform louver assemblies having transverse and longitudinal blades of equal heights, spacings, and surface profiles are very common. They typically are used to construct low-profile, low-brightness luminaires with consistent vertical shielding from all horizontal viewing angles regardless of the position, orientation, and number of lamps (light sources).  
         [0016]     Such uniform louver assemblies, however, have two disadvantages. The first disadvantage adversely affects the efficiency of the luminaire. When louver blades are closely spaced to reduce louver height (and thus advantageously reduce the luminaire height profile) while maintaining the shielding angle, the number and total cross-sectional area of louver blades increases, causing the total open aperture area of the louver to accordingly decrease. This increases the interception and reflection of light rays by louver blades. Typically, luminaire louver blades have a surface reflectance of about 85% to 90%, meaning that about 10% to 15% of the light striking the surface is absorbed (i.e., lost). Consequently, the overall light output of the luminaire decreases and the amount of energy (wattage) required to produce a given lighting level increases. The efficiency and overall performance of the luminaire are therefore lower.  
         [0017]     The second disadvantage of uniform louver assemblies adversely affects the maximum intensity angle. Normally, light rays entering the louver assembly either emanate directly from the lamp or have been redirected to desirable angles by a luminaire reflector. Louvers therefore should only intercept and redirect those light rays emanating directly from the lamp at undesirable angles (i.e., those light rays that have the potential to cause direct brightness and glare). However, some louver blades intercept light rays that are already directed at desirable angles, while not intercepting light rays directed at undesirable angles. This is especially common with respect to longitudinal louver blades in single-lamp linear fluorescent luminaires. Each time a light ray encounters a louver blade surface, it is redirected at a generally higher angle. Thus, redundant louver reflections cause the luminaire output to become more concentrated and to exit the aperture at higher vertical angles. This reduces the luminaire&#39;s ability to output high intensities at low vertical angles (i.e., near the shielding angle) and disadvantageously leads to less light diffusion and reduced surface (e.g., ceiling) uniformity. This, in turn, adversely affects visual comfort and the general appearance of a space.  
         [0018]     In view of the forgoing, it would be desirable to be able to provide a louver assembly that improves the performance of luminaires used for indirect ambient lighting.  
         [0019]     It would also be desirable to be able to provide a louver assembly that improves luminaire efficiency.  
         [0020]     It would further be desirable to be able to provide a louver assembly that produces a wide spread light distribution pattern with maximum light intensities at low vertical angles.  
       SUMMARY OF THE INVENTION  
       [0021]     It is an object of this invention to provide a louver assembly that improves the performance of luminaires used for indirect ambient lighting.  
         [0022]     It is also an object of this invention to provide a louver assembly that improves luminaire efficiency.  
         [0023]     It is further an object of this invention to provide a louver assembly that produces a wide spread light distribution pattern with maximum light intensities at low vertical angles.  
         [0024]     In accordance with the invention, a louver assembly is designed to be positioned in or over the light-emitting opening of a luminaire&#39;s housing. The luminaire includes a lampholder for a light source and preferably a reflector that redirects light from the source at desirable angles above a specified shielding angle. The louver assembly includes a plurality of longitudinal and transverse blades dividing the light-emitting opening into a plurality of apertures. The louver blades are sized, shaped, and arranged to (1) shield the light source from view at angles less than the shielding angle, (2) improve luminaire efficiency, and (3) produce a wide spread light distribution pattern with maximum light intensities at low vertical angles. The louver assembly advantageously reduces the unintended interception and redirection of desirable direct and reflected light rays exiting the opening of the luminaire.  
         [0025]     Embodiments of the louver assembly include one or more of the following features in accordance with the invention: differently sized apertures, louver blades having different curvatures on their longitudinal sides, transversely wider apertures directly over (or under) the luminaire&#39;s lamp(s) (e.g., no longitudinal louver blades centered over (or under) the lamp(s)), longitudinal louver blades that are nonplanar with transverse louver blades, and louver blades having different heights. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     The above and other objects and advantages of the invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:  
         [0027]      FIGS. 1 and 2  are cross-sectional and partial longitudinal views, respectively, of a typical baffle assembly;  
         [0028]      FIG. 3  is a perspective view of a luminaire employing the baffle assembly of  FIGS. 1 and 2 ;  
         [0029]      FIGS. 4   a,b  are cross-sectional and partial longitudinal views, respectively, of the luminaire of  FIG. 3  positioned for uplighting;  
         [0030]      FIG. 5  is a candlepower distribution curve representing the luminous output in the transverse plane of the luminaire of  FIG. 4   a;    
         [0031]      FIGS. 6-8  are cross-sectional, partial longitudinal, and partial perspective views, respectively, of a typical uniform louver assembly;  
         [0032]      FIG. 9  is a cross-sectional view of a luminaire with a typical louver assembly showing disadvantageous redirection of light rays;  
         [0033]      FIG. 10  is a candlepower distribution curve representing the luminous output in the transverse plane of the luminaires of  FIGS. 4   a  and  9 ;  
         [0034]      FIGS. 11-13  are cross-sectional views of a luminaire with a typical louver assembly showing advantageous interception of undesirable lamp emanations, disadvantageous redirection of lamp emanations, and disadvantageous interception of advantageously reflected light rays, respectively;  
         [0035]      FIGS. 14-16  are cross-sectional views of a luminaire with another embodiment of a typical louver assembly showing advantageous interception of undesirable lamp emanations, disadvantageous redirection of lamp emanations, and disadvantageous interception of advantageously reflected light rays, respectively;  
         [0036]      FIG. 17  is a cross-sectional view of a first embodiment of a louver assembly according to the invention;  
         [0037]      FIG. 17   x  is an enlarged cross-sectional view of a longitudinal louver blade of the louver assembly of  FIG. 17  according to the invention;  
         [0038]      FIG. 18  is a cross-sectional view of a luminaire employing the louver assembly of  FIG. 17 ;  
         [0039]      FIG. 19  is a candlepower distribution curve representing the luminous output in the transverse plane of the luminaires shown in  FIGS. 4   a ,  9 , and  18 ;  
         [0040]      FIGS. 20   a,b  are cross-sectional views of another embodiment of a louver assembly according to the invention;  
         [0041]      FIGS. 21   a,b  are cross-sectional and partial perspective views, respectively, of another embodiment of a louver assembly according to the invention;  
         [0042]      FIG. 22  is a cross-sectional view of still another embodiment of a louver assembly according to the invention;  
         [0043]      FIG. 23  is a cross-sectional view of the luminaire of  FIG. 18  showing disadvantageous interception of advantageously reflected light rays;  
         [0044]      FIGS. 24 and 25  are perspective and cross-sectional views, respectively, of another embodiment of a louver assembly according to the invention;  
         [0045]      FIG. 26  is a perspective view of a luminaire employing several louvers of  FIGS. 24 and 25 ;  
         [0046]      FIG. 27  is a cross-sectional view of another luminaire employing the louver of  FIGS. 24 and 25  in which unobstructed and advantageously redirected light rays are shown exiting the luminaire;  
         [0047]      FIG. 28  is a candlepower distribution curve representing the luminous output in the transverse plane of the luminaires shown in  FIGS. 9, 18 , and  27 ;  
         [0048]      FIGS. 29 and 30  are perspective and cross-sectional views, respectively, of another embodiment of a louver assembly according to the invention;  
         [0049]      FIG. 30   x  is an enlarged cross-sectional view of a portion of the louver assembly of  FIGS. 29 and 30 ;  
         [0050]      FIG. 31  is a partial longitudinal view of the louver assembly of  FIGS. 29 and 30 ;  
         [0051]      FIG. 32  is a perspective view of a luminaire employing the louver assembly of  FIGS. 29-31 ;  
         [0052]      FIG. 33  is a cross-sectional view of the luminaire of  FIG. 32  showing unobstructed and advantageously redirected light rays exiting the luminaire;  
         [0053]      FIGS. 34   a,b  are cross-sectional and partial perspective views, respectively, of another embodiment of a louver assembly according to the invention;  
         [0054]      FIGS. 35   a,b  are cross-sectional and partial perspective views, respectively, of still another embodiment of a louver assembly according to the invention;  
         [0055]      FIGS. 36   a,b  are cross-sectional and partial perspective views, respectively, of yet another embodiment of a louver assembly according to the invention;  
         [0056]      FIGS. 37   a,b  are cross-sectional and partial perspective views, respectively, of a further embodiment of a louver assembly according to the invention;  
         [0057]      FIGS. 38   a,b  are partial top and partial cross-sectional views, respectively, of a circular embodiment of a louver assembly according to the invention; and  
         [0058]      FIGS. 39   a,b  are partial top and cross-sectional views, respectively, of a concentric embodiment of a louver assembly according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0059]      FIGS. 1 and 2  illustrate how a typical low-brightness baffle assembly controls glare by establishing a shielding angle. Side members and cross (transverse) baffle blades intercept light rays that exit the lamp within the shielding angle. The baffle side members and cross blades are formed with curved profiles and specular finishes to control the redirected rays such that they exit the luminaire in desirable directions that do not violate the shielding angle. Consequently, the viewer is not subjected to direct brightness from the lamp or reflected brightness from the baffle side members and cross blades when viewing the luminaire at sightlines within the shielding angle. The baffle side members advantageously cause the highest angle reflected rays to exit the luminaire parallel to the shielding angle. This contributes to a wide spread distribution. Internal reflectors typically direct all other light rays exiting the luminaire away from the shielding angle. Such luminaires commonly achieve a desirable low-brightness appearance.  
         [0060]     Baffles are commonly used in downlight luminaires, as shown in  FIG. 3 , but are also equally effective for uplighting, as shown in  FIGS. 4   a,b . However, for a given size lamp and shielding angle, the minimum luminaire height profile is dictated by the aperture width. That is, as the aperture width increases, the luminaire height profile increases (because the lamp needs to be positioned farther away from the aperture in order to maintain the shielding angle) and vice versa.  
         [0061]     The candlepower distribution curve shown in  FIG. 5  illustrates the performance of luminaire  400  in which the lamp is a linear fluorescent and, in addition to the baffle assembly, internal reflectors  401  redirect light at (low) angles that do not violate the shielding angle. Commonly, this is referred to as a wide spread or “batwing” distribution. In particular, φ 0  is the maximum light intensity produced by luminaire  400 , angle α 0  is the angle of maximum light intensity, and the shielding angle is 26°.  
         [0062]      FIGS. 6 and 7  illustrate how a typical louver assembly controls glare by establishing a shielding angle. A shielding angle is determined by the louver height and blade spacing. The use of contoured side members and louver blades along with specular finishes is known to achieve low-brightness and high performance. The height of each longitudinal and transverse louver blade is commonly equal to the louver height and, although slight variations in blade surface profiles may require louver blade spacings a and a′ to vary slightly from each other and across the transverse width of the louver, the louver blades and side members are essentially arranged in a uniform array as shown in  FIG. 8 . As with baffles, louvers are equally applicable to downlight and uptight applications.  
         [0063]     Notably, however, the luminaire shielding angle and minimum luminaire height are not a function of aperture width. Luminaire shielding angle is solely a function of blade spacing (e.g., a or a′) and louver height as defined in  FIGS. 6 and 7 . Consequently, variations in aperture width and lamp position do not affect the shielding angle and, for any given lamp size and position, the minimum luminaire height profile is defined by the louver height.  
         [0064]      FIG. 9  illustrates how uniform louver blade contours (i.e., side profiles/curvatures/shapes) limit performance. In this example, the louver side members and both sides of each of the longitudinal louver blades have identical parabolic shapes. Light rays emanating directly from the lamp that strike the inside surface of the longitudinal blades (i.e., the surface facing the lamp) are advantageously redirected at an angle parallel to the shielding angle. However, light rays striking the outside surface of the longitudinal blades (i.e., the surface facing away from the lamp) have already been redirected at advantageous angles close to the shielding angle by luminaire reflector  901 . The subsequent redirection (to higher angles) by the parabolic louver surfaces of these already reflected lights rays is undesirable and diminishes the wide spread output of the luminaire.  
         [0065]     The result is illustrated in  FIG. 10 , where the performance of luminaire  900  is compared with the performance of luminaire  400  (which has the baffle). In particular, louver  600  results in a maximum light intensity of φ 1  and an angle of maximum intensity α 1 . The shielding angle again is 26°. Notably, although a lower profile luminaire can be constructed with the louver, peak candlepower in the transverse plane is significantly reduced and the difference between the peak candlepower angle α 1  and the shielding angle is significantly greater than that obtained with a baffle assembly.  
         [0066]      FIGS. 11-13  further illustrate how a known louver assembly limits the performance of luminaires. Note that in the known louver embodiment shown, the lamp is positioned between and below two longitudinal louver blades. The unshaded portions of those two longitudinal louver blades are superfluous. That is, they add nothing to the establishment of a shielding angle and do not improve luminaire performance. As shown in  FIG. 11 , they do not intercept undesired direct lamp emanations, and thus do not contribute to reducing glare. To the contrary, as shown in  FIG. 12 , those superfluous louver blade segments disadvantageously intercept desirable lamp emanations (exiting the lamp above the shielding angle). Moreover, other desirable light rays, which had already been desirably reflected by reflector  1301 , as shown in  FIG. 13 , are similarly undesirably intercepted by the two superfluous louver blade segments. As described previously, these unnecessary interceptions negatively impact luminaire efficiency. Furthermore, in typical uniform louver assemblies (where all louver blades are identically fashioned to elevate, by reflection, low-angle lamp rays to angles above the shielding angle), the superfluous louver blade sections only disadvantageously redirect desirable light rays to angles farther away from the shielding angle and thus do not contribute to achieving a wide spread distribution (see, e.g.,  FIG. 12 ).  
         [0067]      FIGS. 14-16  illustrate another known uniform louver assembly that limits luminaire performance. In this embodiment, the lamp is positioned directly beneath a center longitudinal louver blade. The luminaire also includes internal reflectors  1401  that direct light rays at angles at or above the shielding angle. The uniform blade spacings again result in superfluous and/or partially superfluous louver blades. In particular, the center louver blade is entirely unnecessary. Moreover, top portions of the two longitudinal louver blades adjacent the center blade are also superfluous, because they receive only (1) direct lamp rays exiting above the shielding angle and (2) advantageously reflected light rays. Again, the interception and reflection of desirable light rays to higher angles above the shielding angle adversely affects the wide spread output of the luminaire. Furthermore, the center blade unnecessarily reduces the total open aperture area of the luminaire, adversely affecting the luminaire&#39;s efficiency (i.e., the percentage of light generated by the luminaire that is emitted from the luminaire).  
         [0068]      FIGS. 17 and 17   x  show an embodiment of a louver assembly in accordance with the invention. Louver assembly  1700  has longitudinal baffle blades having longitudinal inner sides b and outer sides c. Inner sides b receive direct light rays from the lamp, while outer sides c do not. As better seen in  FIG. 17   x , inner sides b and outer sides c have different curvatures (i.e., shapes, profiles, contours) in accordance with the invention. The curvature of outer sides c are such that reflected light rays incident thereon are advantageously redirected parallel to (or close to) the shielding angle. In this embodiment, outer sides c are preferably flat, planar surfaces that have a minimal effect on the angle of incident light with respect to the shielding angle. The curvature of inner sides b, in contrast, preferably has a radius R 1  as shown in  FIG. 17   x . Note that longitudinal sides b and c, as well as the louver cross blades and side members, may have other curvatures than those shown. In as much as the curvature of these blade surfaces defines in part the distance x between the bottom edges of adjacent longitudinal blades (which in turn affects the transverse shielding angle), louver blade spacing a, between two inward curved blade surfaces, may be slightly greater than spacing a″, which is the spacing between one flat and one curved blade side. Alternatively, louver assembly  1700  may have a uniform longitudinal blade spacing of a″.  
         [0069]      FIG. 18  shows a luminaire  1800  that includes louver assembly  1700 . Reflected light rays that would otherwise be redirected away from the shielding angle by known louver assemblies are instead advantageously redirected to angles close to the shielding angle in accordance with the invention.  
         [0070]     The advantageous result is shown in  FIG. 19 , where the performance of luminaire  1800  (shown in bold) is compared with known luminaires  400  (which has a baffle assembly) and  900  (which has a known uniform louver assembly). In particular, φ 1  and φ 2  both represent, respectively, the maximum intensity achieved with the louver of invention and known uniform louver  600  of luminaire  900  ( FIG. 9 ). φ 0  represents the maximum intensity achieved with the baffle assembly of luminaire  400  ( FIG. 4   a ). Angle α 2  is the angle of maximum intensity produced by the louver of the invention, and the shielding angle again is 26°. Angles α 0  and α 1  are the angles of maximum intensity for luminaires  400  and  900 , respectively. Advantageously, the louver of invention achieves a distribution where the angle of maximum intensity (angle α 2 , which is 44°) is 30% closer to the shielding angle than angle α 1  achieved by known uniform louver assembly  600 . Accordingly, angle α 2  is equal to that achieved by the baffle assembly (see angle α 0 ). Also significant is that the intensity (φ 2 ) achieved at angle α 2  is about 7% greater than that achieved by known uniform louver  600  at the same angle. More significant is that the louver of the invention achieves a 20% increase in output at an angle just 10° above the shielding angle when compared with that of known uniform louver  600 .  
         [0071]     Although luminaire efficiency and maximum intensity is essentially unchanged by the louver of the invention when compared with known uniform louver assembly  600  of luminaire  900 , the resulting wide spread distribution achieves greater uniformity of surface (e.g., ceiling) brightness and greater visual comfort, particularly in furniture/partition mounted luminaires.  
         [0072]      FIGS. 20   a,b  illustrate another embodiment of a louver assembly in accordance with the invention. Louver assembly  2001  is incorporated in a luminaire  2000  employing two parallel elongated lamps  2002  and  2004 . Center longitudinal louver blade  2006  has two identically curved sides, while the other longitudinal louver blades have one planar and one curved side each. Two of these other longitudinal louver blades occur directly over the lamps. While the flat sides of these two blades receive some direct lamp emanations from the respective lamp immediately below them, they receive no direct light rays from the respective other lamp, and their direct exposure is limited to high angle light rays that are redirected above the shielding angle.  FIG. 20   b  illustrates the advantageous redirection of light rays parallel to the shielding angle, which results in a wide spread distribution.  
         [0073]      FIGS. 21   a,b  illustrate another embodiment of a louver assembly in accordance with the invention. Louver assembly  2101  is positioned in the top aperture of a direct/indirect luminaire  2100 . Louver assembly  2101  establishes shielding for sightlines originating above the luminaire. In this embodiment, the shielding angle is again 26° (other angles are, of course, possible) and the angle of maximum uptight intensity provided by louver  2101  advantageously occurs within 15° of the shielding angle. The louver is formed with extended side members that integrate additional reflector segments d into the assemblies. The louver also includes horizontal top extensions f that facilitate mounting. The louver further has cross-blade fillets e that facilitate production when the extended side members are formed by injection molding. Cross-blade extensions e′ allow the transverse blades to be uniquely fashioned below the longitudinal shielding line to divert light rays that otherwise would be disadvantageously redirected by the bottom surfaces of the blades toward the downlight reflectors t.  
         [0074]      FIG. 22  illustrates still another embodiment of a louver assembly in accordance with the invention. Louver assembly  2201  is positioned in the top aperture of a direct/indirect luminaire. Louver  2201  is fashioned and positioned in luminaire  2200  for a lamp position different than that of luminaire  2100  and for providing a shielding angle of 35° instead of 26°. Again, the louver is formed with extended side members that integrate additional reflector segments h into the assemblies. Louver  2201  also includes horizontal top extensions f that facilitate mounting. Cross-blade fillets j facilitate one-piece molding techniques, and cross-blade extensions j′ control the angle of light rays reflected from the bottom surfaces of the cross-blades. Advantageously, the angle of maximum uplight intensity again occurs within 15° of the shielding angle.  
         [0075]      FIG. 23  again shows louver assembly  1700  positioned in luminaire  1800  (from  FIG. 18 ). Louver assembly  1700  has substantially uniform longitudinal louver blade spacings and uniform blade heights. And while the wide spread distribution of luminaire  1800  is improved by louver  1700  having longitudinal blades with different longitudinal side curvatures, the performance of luminaire  1800  can be further improved by modifying louver  1700  in accordance with the invention.  
         [0076]     As shown in  FIG. 23 , reflector  2301  advantageously redirects light rays at angles above and preferably parallel to the shielding angle. Note that the two center longitudinal louver blades  2303  and  2305  (shown unshaded) unnecessarily intercept those desirable light rays. And although the planar side of louver blade  2303  will redirect in a desirable direction the light rays striking it (see  FIG. 18 ), recall that each reflectance of light striking a louver blade loses about 10% to 15% of that light. This adversely affects luminaire efficiency. Moreover, the light shown striking louver blade  2305  will be redirected at an undesirably higher angle. The same is true for light striking louver blades  2303  and  2305  from the right side of luminaire  1800  (not shown).  
         [0077]     Therefore, in accordance with the invention, a further improved louver assembly is shown in  FIGS. 24 and 25 . Louver assembly  2400  is similar to louver  1700  except that the superfluous center longitudinal blades are omitted. The apertures of louver  2400  are thus of non-uniform size. Larger apertures are found over the lamps, thus allowing more light to exit the luminaire, improving efficiency, while smaller apertures are transversely adjacent the larger apertures (note transverse widths e and d in  FIG. 25 ). In particular, transverse width d is greater than transverse widths e.  
         [0078]     The longitudinal blades of louver  2400  preferably have longitudinal sides with different curvatures b and c as shown. In this embodiment, curvature b is preferably parabolic, while curvature c is preferably planar. Alternatively, other curvatures may be used, and they need not be different from each other (although some benefit may be lost depending on the angles at which those curvatures redirect light).  
         [0079]      FIGS. 26 and 27  show luminaires incorporating louver  2400 . Luminaire  2600  includes several louver assemblies  2400 .  FIG. 27  shows large numbers of reflected light rays that are advantageously no longer intercepted and redirected away from the shielding angle, thus improving both efficiency and the wide spread distribution pattern. Moreover, the longitudinal blades advantageously redirect the direct emanations from lamp  2702  and the reflected light from reflector  2701  at low angles parallel to the shielding angle.  
         [0080]     These advantageous results are shown in  FIG. 28 , where the performance (shown in bold) of louver  2400  in luminaire  2700  is compared with that of the louvers in luminaires  900  and  1800  of  FIGS. 9 and 18 , respectively. In particular, louver  2400  results in a maximum intensity of φ 3  and an angle of maximum intensity α 3 . The shielding angle again is 26°. Louver  2400  achieves a distribution where the angle of maximum intensity closely approximates that achieved by louver assembly  1700  (i.e., the louver with strategically shaped longitudinal blades). However, the maximum intensity φ 3  achieved at angle α 3  is 5% greater than that achieved by louver  1700  and is about 12% greater than that achieved by known uniform louver assembly  600  at the same angle. Maximum intensity φ 3  is accordingly also about 5% greater than the maximum intensity achieved by louver assembly  600  at any angle (recall that φ 1  approximates φ 2 ). More significantly, louver  2400  achieves a 28% increase in output at an angle just 10° above the shielding angle when compared to known uniform louver assembly  600 . The resulting wide spread distribution achieves greater uniformity of surface (e.g., ceiling) brightness and greater visual comfort than that possible with known louvers, particularly in furniture/partition mounted luminaires.  
         [0081]      FIGS. 29-33  show another embodiment of a louver assembly in accordance with the invention. Louver  2900  has two interior longitudinal louver blades  2902  and  2904  that each have a height less than that of the louver side members and cross (transverse) blades. In other words, the tops of the longitudinal blades are nonplanar with the tops of the side members and cross blades, where “top” is defined as the side farthest from the luminaire lamp(s). Louver blades  2902  and  2904  preferably have longitudinal sides of different curvatures (e.g., curvatures k and h′ as shown in  FIG. 30   x , which may be planar and parabolic, respectively), and cross blades  3006  are preferably uniformly spaced by a distance m ( FIG. 31 ). In one embodiment of the invention, the inner (lamp facing) side of louver side members  3008  ( FIGS. 30 and 30   x ) preferably have a surface curvature formed by two parabolic shapes h and j that have a common edge coincident with line j′. Line j′ passes through point f 2  and is tangent to the top of lamp  3007 . Specifically, shapes h and j have focal points f 1  and f 2 , respectively, that are coincident with the lowest angle direct lamp rays incident to the respective shapes. Shapes h and j advantageously redirect these lamp rays (and all other light rays passing through the respective focal points) parallel to the shielding angle. Note that the longitudinal blades, as well as the side members, are not limited to having one shape per longitudinal side, but alternatively can have multiple shapes per longitudinal side.  
         [0082]      FIGS. 32 and 33  show luminaire  3200  fitted with louver assembly  2900 . Louver  2900  reduces the obstruction and disadvantageous redirection of light rays exiting the luminaire near the shielding angle. Moreover, louver  2900  advantageously redirects obstructed rays to angles close to the shielding angle, thus achieving high luminaire efficiency and a wide spread distribution. Note that the overall aperture width of the louver relative to the shielding angle, louver height, and location of the lamp determines the height x (see  FIG. 30   x ) of louver blades  2902  and  2904 .  
         [0083]      FIGS. 34   a,b  show another embodiment of a louver assembly in accordance with the invention. Louver assembly  3401  is positioned in the top aperture of a direct/indirect luminaire  3400 . Louver  3401  establishes shielding for sightlines originating above luminaire  3400 . The tops of the longitudinal blades are nonplanar with the tops of the side members and cross blades. The longitudinal blades preferably have longitudinal sides with different curvatures as described above. In this embodiment, the shielding angle is 35°, and the louver is formed with extended side members that advantageously integrate additional reflector segments n into the assemblies. Horizontal top extensions s advantageously facilitate mounting of the louver in a luminaire. Cross-blade fillets p facilitate production when louver  3401  is formed by injection molding, and cross-blade extensions p′ allow transverse blades  3406  to be uniquely fashioned below the longitudinal shielding line to divert light rays that otherwise would be disadvantageously redirected by the bottom surfaces of the blades toward downlight reflectors t. Louver  3401  advantageously produces an angle of maximum uptight intensity that occurs within 15° of the shielding angle.  
         [0084]      FIGS. 35   a,b  show still another embodiment of a louver assembly in accordance with the invention. Louver assembly  3501  is positioned in the top aperture of a direct/indirect luminaire  3500 . Louver  3501  is fashioned uniquely for a lamp position differing from that of luminaire  3400  and for producing a shielding angle of 26°. Again, the louver is formed with extended side members that integrate additional reflector segments q into the assemblies. Louver  3501  also has horizontal top extensions s that facilitate mounting of the louver in a luminaire. Cross-blade fillets r facilitate one-piece molding techniques, and cross-blade extensions r′ control the angle of light rays reflected from the bottom surfaces of the cross-blades. Notably, as in the previous two embodiments, the tops of the two interior longitudinal louver blades are nonplanar with and lie below (although slightly in this embodiment) the tops of the cross blades and side members. The longitudinal blades preferably have longitudinal sides with different curvatures as described above. The angle of maximum uptight intensity produced by louver  3501  again advantageously occurs within 15° of the shielding angle.  
         [0085]      FIGS. 36   a,b  show yet another embodiment of a louver assembly in accordance with the invention. Louver assembly  3601  is positioned in the top aperture of a direct/indirect luminaire  3600 . Louver  3601  is fashioned uniquely for a pair of lamps or twin-tube lamp to produce a shielding angle of 35°. Again, the louver is formed with extended side members that integrate additional reflector segments v into the assemblies. Louver  3601  is also formed with horizontal top extensions s that facilitate mounting of the louver in a luminaire. Louver  3601  is further formed with cross-blade fillets w to facilitate one-piece molding techniques. Cross-blade extensions w′ control the angle of light rays reflected from the bottom surfaces of the cross blades. Notably, although the overall height of the two interior longitudinal louver blades is substantially similar to the effective height of the transverse louver blades (i.e., the height of the cross blades above the longitudinal shielding line), the tops of the longitudinal blades are set below the tops of the cross blades and side members (i.e., the tops are nonplanar) and, accordingly, the longitudinal louver blades extend beyond and below the longitudinal shielding line.  
         [0086]      FIGS. 37   a,b  show a further embodiment of a louver assembly in accordance with the invention. Louver assembly  3701  is positioned in the top aperture of a direct/indirect luminaire  3700 . In this embodiment, the tops of longitudinal blades  3702  and  3704  are planar with the tops of side members  3708  and  3710  and the cross blades. The cross blades are made up of either both outboard and center blade sections  3705  and  3706 , or only center blade section  3706 .  
         [0087]     Because the longitudinal louver blades advantageously extend inward (i.e., downward as shown in  FIG. 37   a ) and beyond the longitudinal shielding line of the center cells, the minimum effective aperture cell depth (designated y′) of the outboard aperture cells is greater than the aperture cell depth (designated y) of the center aperture cells. Therefore, the spacing of the outboard cross blades can be increased relative to that of the center cross blades. Accordingly, the curved, low-brightness profile of the outboard cross blades is extended to a longitudinal shielding line occurring at a depth coinciding with the increased effective depth of the outboard cells. Specifically, in this embodiment, the shielding angle is 26° and the effective depth of the outboard louver cells y′ is approximately twice the effective depth y of the center cells such that the spacing of the outboard cross blades is twice that of the center cross blades.  
         [0088]     Other relative depth and spacing relationships are possible, including the omission of outboard cross blades  3705  entirely as suggested above, because any low angle direct lamp emanations they receive will otherwise be redirected to desirable angles by the adjacent (intersecting) side members. (In some constructions, however, these outboard cross blades may serve to position and/or support the longitudinal and center cross blades or prevent direct view of non-optical features within the luminaire.)  
         [0089]     Notably, the performance of louver  3701  is substantially equivalent to the performance of louver  3501 . While potentially more difficult to fabricate than louver assembly  3501 , louvers such as  3701  employ cross blades of reduced height profile directly over the lamp (albeit there being more center cross blades at a reduced blade-to-blade spacing than louver  3501 ). This reduced height profile provides greater clearance between the lamp and the louver assembly, which may allow higher wattage (hotter) lamps to be used. Alternatively, the reduced louver height profile, combined with an increase in the size of the outboard aperture cells, may allow the luminaire height profile to be further reduced without adversely affecting efficiency.  
         [0090]     Louvers of the invention may also be used in direct luminaires, where the louver assembly is mounted in a light emitting opening in the bottom of the luminaire. Accordingly, louvers of the invention may further be used in direct/indirect luminaires having openings in their tops and bottoms, where the louver assembly may be mounted in the top opening (as shown in the embodiments above), the bottom opening, or both. Louvers of the invention may still further be used in luminaires employing multiple lamps, compact fluorescent lamps, circular type lamps, point sources such as tungsten-halogen and high-intensity discharge lamps, as well as other types of light sources. Furthermore, louvers of the invention may have non-orthogonal, concentric, and radial blade arrangements for use in luminaires with non-elongated light sources.  FIGS. 38   a,b  and  FIGS. 39   a,b  show such alternative embodiments of louver assemblies in accordance with the invention.  
         [0091]     Thus it is seen that high performance louvers and luminaires are provided. One skilled in the art will appreciate that the invention can be practiced by other than the described embodiments, which are presented for purposes of illustration and not of limitation, and the present invention is limited only by the claims which follow.