Radiation-redistributive devices

Abstract

Devices for redistributing incident radiation in a prescribed manner. Such devices comprise a multitude of contiguous optical microelements, each of such microelements being contoured and oriented to redistribute incident radiation, emanating from an intended irradiating source, only throughout an angular field just large enough to encompass a predefined region wherein the redistributed radiation has particular utility. Moreover, the contour and orientation of each microelement is such as to produce substantially uniform radiance throughout such predefined region of utility, and to redirect extraneous or undesirable radiation incident thereon away from said predefined region. The radiation-redistributive devices of the invention are particularly useful as front or rear projection screens, lighting reflectors or refractors, illumination aids for photographic prints, traffic signs, advertisements, etc.

We claim: 
     
       1. A radiation-redistributive device having a surface defining a plurality of parallel grooves, each of said grooves having a depth which undulates along the groove length to define a row of alternately concave and convex optical microelements, each of said microelements being contoured to redistribute incident radiation in such a manner as to produce substantially uniform radiance throughout predefined vertical and horizontal field angles and being disposed such that a plane which bisects one of its field angles and which extends .[.perpendicular.]. .Iadd.transverse .Iaddend.to the groove length intersects with similarly defined planes of all other microelements substantially along a first line which extends parallel to said surface and is in a plane perpendicular to the groove length. 
     
     
       2. The invention according to claim 1 wherein said surface is cylindrically curved about said first line. 
     
     
       3. The invention according to claim 1 wherein said grooves are rectilinear. 
     
     
       4. The invention according to claim 3 wherein said grooves are contiguously arranged to form cusp lines at the juncture of adjacent grooves, said cusp lines undulating in a plane perpendicular to said surface and extending substantially parallel to the groove length. 
     
     
       5. The invention according to claim 1 wherein each of said microelements is disposed such that the plane which bisects the other of its field angles and which extends parallel to the groove length intersects with similarly defined planes of all microelements substantially along a second line which perpendicularly intersects said first line and is in a plane parallel to the screen surface. 
     
     
       6. The invention according to claim 5 wherein said grooves are rectilinear. 
     
     
       7. The invention according to claim 5 wherein said surface is cylindrically curved about said second line. 
     
     
       8. The invention according to claim 5 wherein said surface is substantially reflective so as to reflect radiation emanating from a source on one side of the screen to a field situated on the same side of the screen as the source. 
     
     
       9. The invention according to claim 5 wherein the screen, including said surface, is substantially transparent so as to refract radiation emanating from a source on one side of the screen to a field situated on the opposite side of the screen from the source. 
     
     
       10. The invention according to claim 5 wherein said surface is spherically curved about the intersection of said first and second lines. 
     
     
       11. A projection screen for presenting a predefined field of observation an image projected thereon by a projecting apparatus, said screen having a surface defining a plurality of contiguous grooves, each of said grooves having a depth which periodically undulates along the groove length and thereby defines a row of alternately concave and convex optical microelements, each of said grooves having a transverse cross section which is substantially defined by at least a segment of a first curve ##EQU3## where w and u are the coordinates of said curve, w being measured in a direction parallel to the path of incident image light, u being measured in a direction perpendicular to w and in the plane of the cross section; and n is the refractive index of the microelement (n being -1 when the microelement is reflective); and w has a value with the limits: -≦ w≦-cos 2  (B + θ'), when g(w;n) is positive and the microelement is refractive;   -1≦w≦-cos 2  (A - θ'), when g(w;n) is negative and the microelement is refractive;   -1≦w≦-cos 2  (A - θ), when g(w;n) is positive and the microelement is reflective; and   -1≦w≦-cos 2  (B + θ), when g(w;n) is negative and the microelement is reflective; where θ is the projection in the u - w plane of the angle formed by a line extending parallel to incident image light, and the normal to the screen surface; n = sin θ/sin θ'; and A and B are the audience angles, measured from a normal to the screen surface and in the plane of the cross section, through which incident image light must be distributed to just encompass said field of observation.     
     
     
       12. The invention according to claim 11 wherein each of said microelements has a longitudinal cross section, taken in a plane parallel to the groove length and normal to said surface, substantially defined by at least a segment of said first curve, and A and B and u are measured in the plane of said longitudinal cross section, and by at least a segment of a second curve ##EQU4## where w has a value within the following limits: cos 2  (A - θ')≦ w≦ 1, when f(w;n) is positive and the microelement is refractive; cos.sup. 2 (B + θ')≦w≦ 1, when f(w;n) is negative and the microelement is refractive;   cos 2  (B + θ)≦w≦ 1, when f(w;n) is positive and the microelement is reflective;   cos 2  (A - θ)≦w≦ 1 when f(w;n) is negative and the microelement is reflective.   
     
     
       13. A rear projection screen for presenting an image projected thereon to a predefined audience space, said screen comprising a sheet of substantially transparent material having a first surface comprising means defining a plurality of contiguous grooves each of said grooves having a transverse cross section defined by at least a segment of the curve ##EQU5## where w and u are the curve coordinates, w being measured in a direction parallel to the path of incident image light, u being measured in a direction perpendicular to w and in the plane of the cross section; n is the refractive index of said material, and w has a value within the limits -≦ w≦ -cos 2  (B + θ'), when g(w;n) is positive, and   -1≦w≦ -cos 2  (A - θ'), when g(w;n) is negative; where A and B are the angles, measured from the normal to said first surface in the plane of the cross section, through which each groove redistributes image light to just encompass said audience space, and sin θ' = sin θ/n, where θ is the projection in the u - w plane of the angle formed by the line extending parallel to incident image light and the normal to said first surface.     
     
     
       14. The invention according to claim 13 wherein said first surface is substantially planar, and said sheet of material has a second surface, spaced from and extending substantially parallel to said first surface, comprising means defining a Fresnel-type lens. 
     
     
       15. The invention according to claim 14 wherein each of said grooves has a depth which periodically undulates along the groove length to define a row of alternately concave and convex optical microelements. 
     
     
       16. A rear projection screen for presenting an image projected thereon to a predefined audience space, said screen comprising a sheet of substantially transparent material having a first surface comprising means defining a plurality of contiguous grooves, each of said grooves having a transverse cross section defined by at least a segment of the curve ##EQU6## where w and u are the curve coordinates, w being measured in a direction parallel to the path of incident image light and u being measured in a direction perpendicular to w in the plane of the cross section; n is the refractive index of said material, an w has a value within the following limits; cos 2  (A - θ')≦w≦1, when f(w;n) is positive; and   cos 2  (B + θ')≦w≦ 1, when f(w;n) is negative; where A and B are the angles, measured from the normal to said first surface in the plane of the cross section, through which each groove redistributes incident image light to just encompass said audience space, and sin θ' = sin θ/n, where θ is the projection in the u - w plane of the angle formed by the line extending parallel to incident image light and the normal to said first surface.     
     
     
       17. The invention according to claim 16 wherein said first surface is substantially planar, and said sheet of material has a second surface, spaced from and extending substantially parallel to said first surface, comprising means defining a Fresnel-type lens. 
     
     
       18. The invention according to claim 17 wherein each of said grooves has a depth which periodically undulates along the groove length to define a row of alternately concave and convex optical microelements.