Sunlight redirecting mirror arrays

Sunlight redirector (30) incorporates closely proximate mirror arrays (32, 34) having parallel, uniformly spaced, longitudinal mirror segments (38, 44). Prismatic sheet (36) is positioned behind and closely proximate second array (34). Segments (38) extend in first direction (x). Segments (44) extend in second direction (y) perpendicular to direction (x) segments (38, 44)have normal vectors (42, 48). Segments (38) are interconnected for simultaneous pivotal movement (40), such that their normal vectors (42) remain parallel. Segments (44) are interconnected for simultaneous pivotal movement (46), such that their normal vectors (48) remain parallel. Arrays (32, 34) redirect incident light toward sheet (36), which redirects the light into a desired fixed direction, e.g. parallel to the sunlight redirect's normal vectors (50). Segments (38, 44) may have inward and outward segments (60A, 60B) which can be adjustably positioned to maximize redirection of incident sunlight rays in a desired direction.

TECHNICAL FIELD

This disclosure pertains to mechanisms for redirecting light, particularly sunlight.

BACKGROUND

WO 2009/000070, which is incorporated herein by reference, describes a sunlight redirector in which longitudinally adjacent plane mirrors are pivotally interconnected by non-stretching linkages to form a columnar array (seeFIG. 1hereof). The non-stretching linkages constrain movement of the mirrors such that their normal vectors remain parallel. Pivotable couplings (not shown inFIG. 1hereof, but see WO 2009/000070) permit movement of the mirrors with respect to two mutually perpendicular axes and prevent movement of the mirrors with respect to a third axis which is perpendicular to the other two axes. Actuators (not shown inFIG. 1hereof, but see WO 2009/000070) controllably move the mirrors to orient their normal vectors such that the mirrors reflect incident light in a desired direction. The actuators can be adaptively controlled to move the mirrors to track the sun, and thereby continually redirect sunlight into a specific direction, e.g. through a wall opening to illuminate the interior of a building.

Such mirror arrays are useful in building core daylight illumination systems, as explained in WO 2009/000070. It is desirable that such mirror arrays be thin, to facilitate mounting the arrays on or within building walls. A thin mirror array can be formed from a large number of small mirrors. However, a disadvantage of this approach is that the required number of mirrors increases in inverse proportion to the square of the thickness of the array, potentially prohibitively increasing the cost of constructing a suitably thin array. This disclosure addresses that disadvantage.

DESCRIPTION

FIG. 2depicts a sunlight redirector10having a plurality of substantially parallel, uniformly spaced, longitudinal mirror segments12. Segments12are interconnected (not shown) in a manner similar to that used to interconnect Venetian blind slats. A controller (not shown) coupled to one or more of segments12can be selectably actuated to simultaneously pivot all of segments12, as indicated by double-headed arrow14. Segments12can thus be pivotally adjusted, in the manner of a Venetian blind, such that their respective normal vectors16remain parallel. Segments12are of differing lengths, and are arranged such that sunlight redirector10has a circular front elevational shape as seen inFIG. 2. Sunlight redirector10is rotatable about its normal vector18, as indicated by double-headed arrow20.

Sunlight redirector10can thus be rotated to track the sun's azimuthal motion relative to the array's normal vector18, and segments12can be pivotally adjusted to compensate for changes in the sun's altitude, so that light rays reflected by segments12will be redirected in a desired, fixed direction, e.g. substantially parallel to normal vector18to facilitate redirection of light rays through a wall opening to illuminate the interior of a building.

FIGS. 3A,3B and3C illustrate a potential disadvantage of using sunlight redirector10′s segments12to redirect light—redirection efficiency depends on the desired redirection angle.FIG. 3Adepicts a small redirection angle situation in which the mirror segments (represented by solid lines) are nearly parallel to the incident light, so most rays (represented by dashed lines) do not strike the mirrors and are therefore not redirected as desired.FIG. 3Bdepicts an intermediate situation in which the mirror segments are obliquely angled relative to the incident light, with most rays striking the mirrors and being redirected as desired.FIG. 3Cdepicts a situation in which the desired redirection angle is so large that the mirror segments are positioned at such a large oblique angle relative to the incident light that most rays which strike the mirrors are redirected onto an adjacent mirror, then further redirected away from the desired direction. TheFIGS. 3A and 3Csituations are problematic since it is desirable to redirect rays corresponding to a wide range of sun angles.

Another potential disadvantage of sunlight redirector10is possible increased complexity and cost in rotatably moving sunlight redirector10about normal vector18.FIG. 4depicts a stationary sunlight redirector30which addresses the foregoing potential disadvantages.

Stationary sunlight redirector30has a first mirror array32, a second mirror array34and a prismatic sheet36. First mirror array32is formed of a first plurality of substantially parallel, uniformly spaced, longitudinal mirror segments38. Segments38are mirrored on either one or both sides, depending on the expected range of directions of the incident sunlight; and are interconnected (not shown) in a manner similar to that used to interconnect Venetian blind slats. A controller (not shown) coupled to one or more of segments38can be selectably actuated to simultaneously pivot all of segments38, as indicated by double-headed arrow40. Segments38can thus be pivotally adjusted, in the manner of a Venetian blind, such that their respective normal vectors42remain parallel. Segments38are of equal lengths, and are arranged such that first mirror array32has a rectangular front elevational shape as seen inFIG. 4.

Second mirror array34is formed of a second plurality of substantially parallel, uniformly spaced, longitudinal mirror segments44. Segments44are mirrored on either one or both sides, depending on the expected range of directions of the incident sunlight; and are interconnected (not shown) in a manner similar to that used to interconnect Venetian blind slats. A controller (not shown) coupled to one or more of segments44can be selectably actuated to simultaneously pivot all of segments44, as indicated by double-headed arrow46. Segments44can thus be pivotally adjusted, in the manner of a Venetian blind, such that their respective normal vectors48remain parallel. Segments44are of substantially equal lengths, and are arranged such that second mirror array34has a rectangular front elevational shape as seen inFIG. 4.

First mirror array32is positioned in front of and in close proximity to second mirror array34with mirror segments38extending in a first direction x, and mirror segments44extending in a second direction γ which is substantially perpendicular to the first direction x. Prismatic sheet36is positioned behind and in close proximity to second mirror array34.

First mirror array32can be pivotally adjusted to compensate for changes in the sun's altitude such that light rays reflected by segments38are redirected in a desired, fixed direction, e.g. toward prismatic sheet36. Second mirror array34can be pivotally adjusted to compensate for changes in the sun's azimuth such that light rays reflected by segments44are also redirected in a desired, fixed direction, e.g. toward prismatic sheet36.

Light rays redirected toward prismatic sheet36by either of first or second mirror arrays32,34are refracted (i.e. redirected) by prismatic sheet36into a final desired fixed direction substantially parallel to the normal vector50of sunlight redirector30. For example, the final desired fixed direction can be such that the rays are redirected through a wall opening to illuminate the interior of a building. Light rays redirected by first and second mirror arrays32,34are efficiently redirected by prismatic sheet36. Neither first mirror array32alone, nor second mirror array34alone, will efficiently redirect sunlight rays in situations where very little redirection is required. This corresponds to the disadvantage depicted inFIG. 3A. Prismatic sheet36compensates by imparting further substantial redirection of the light rays in such situations, thus improving efficiency. For example, without prismatic sheet36, sunlight redirection efficiency of an array mounted on a south wall would be very low while the sun is due south.

The side of prismatic sheet36facing toward second mirror array34may be flat. The opposite side of prismatic sheet36may bear a large plurality of vertically extending 70° internal whole angle isosceles triangle prisms. Sheet36can be formed of a transparent polymeric material such as polycarbonate (PC), polyethyleneterephthalate (PET), poly methyl methacrylate (PMMA), or a combination of PC, PET and/or PMMA. 2370 optical lighting film available from 3M, St. Paul, Minn. can be used to form sheet36. The precise angle and size of the film's prisms is not highly critical—generally the desired characteristic is that light rays that are oriented roughly 30° (between 10° and 50°) to the left or to the right of perpendicular will be efficiently refracted by the film into a direction which is substantially perpendicular to the macroscopic plane of sheet36. Consequently, light rays redirected by first and second mirror arrays32,34do not need to be perpendicular to sunlight redirector30as a whole—which in any case is a difficult constraint to satisfy at times near solar noon.

Although sheet36improves sunlight redirector30′s efficiency for problematic sun angles (e.g. at times near solar noon), it may not satisfactorily accommodate all desired light redirection angles. Furthermore, light refracted through sheet36may be redirected in slightly different directions, depending on the wavelength of the incident light. These disadvantages can be circumvented as discussed below in relation toFIGS. 5A-5D.

FIGS. 5A-5Deach depict four pairs of longitudinal inward/outward mirror segments60A,60B;62A,62B;64A,64B; and66A,66B (represented by solid lines). Each mirror segment12in sunlight redirector10may be one such pair of inward/outward segments. Similarly, each mirror segment38and/or each mirror segment44in sunlight redirector30may be one such pair of inward/outward segments. Mirror segments60A,60B;62A,62B;64A,64B; and66A,66B are mirrored on both sides.

Outward segments60B,62B,64B and66B are adjustable with respect to inward segments60A,62A,64A and66A respectively.FIG. 5Adepicts adjustment to align the inward and outward segments in each pair substantially parallel to one another.FIG. 5Bdepicts adjustment of the segments to align the outward segment in each pair in a direction which is substantially parallel to the dominant direction of incident sunlight rays (depicted as dashed arrows inFIGS. 5A-5D).FIG. 5Cdepicts adjustment of the segments such that incident light rays are first reflected by the outward segments onto the adjacent inward segments, then further reflected in the desired direction by the inward segments.FIG. 5Ddepicts adjustment of the segments such that incident light rays are first reflected by the inward segments onto the adjacent outward segments, then further reflected in the desired direction by the outward segments.

The different segment adjustment configurations depicted inFIGS. 5A-5Dyield different light redirection efficiencies which depend on factors such as the segments' sizes and the incident light angle. The segments can be automatically selectably adjusted by a suitable control system to adopt any of the depicted adjustment configurations (or any desired intermediate adjustment configuration) in order to maximize light redirection efficiency at different times. Generally, the best choice at any particular time will be the adjustment configuration that minimizes total loss of useful light rays (i.e. light rays which pass through the sunlight redirector without being redirected are “lost” in the sense that they are not redirected into the desired direction). In all cases, the inward/outward mirror segments are adjustably positioned taking into account both the sunlight incidence angle and the desired direction into which the light rays are to be redirected. The required mirror segment positions can be readily determined for any selected sunlight incidence angle by well known ray trace analysis techniques. The so-determined mirror segment position data can be stored in a look-up table or emulated in various forms of open loop mathematical algorithms or feed-back-based closed loop algorithms, or some combination thereof. Such look-up table and algorithmic techniques are well known to persons skilled in the art. In some cases, theFIG. 4stationary sunlight redirector30can be formed without prismatic sheet36, if mirror segments38and/or44are suitably formed of inward/outward segments as aforesaid.

The scope of the claims should not be limited by the preferred embodiments set forth herein, but should be given the broadest interpretation consistent with the description as a whole.