WO2015085060A1

WO2015085060A1 - Daylighting film with glare control

Info

Publication number: WO2015085060A1
Application number: PCT/US2014/068546
Authority: WO
Inventors: Xinyu GI; Weijun Zhou
Original assignee: Dow Global Technologies Llc
Priority date: 2013-12-06
Filing date: 2014-12-04
Publication date: 2015-06-11

Abstract

A light redirecting member including a base layer and a plurality of optical elements (18) extending from a first side of the base layer, wherein at least one of the optical elements includes a contoured lower surface (22) that comprises at least a portion that is reflective and an upper surface spaced from the lower surface. The upper surface includes at least a first portion (26) that is transmissive to incoming sunlight (30), wherein the lower surface is configured to reflect at least a portion of the incoming sunlight at multiple angles toward the upper surface.

Description

DAYLIGHTING FILM WITH GLARE CONTROL

Cross-Reference to Related Applications

This application claims priority to U.S. Provisional Patent Application No. 611912,676, filed December 6 , 2013 the entire contents of which are incorporated herein by reference in its entirety.

Technical Field

The present invention relates to a light guiding film, and more particularly relates to a light redirecting member used on windows for daylighting applications in which sunlight entering a room is redirected in a way that utilizes sunlight more effectively while reducing glare.

Background

Reducing energy usage in buildings can result in significant cost savings for businesses, consumers, and homeowners. One source of energy reduction is to use sunlight more effectively during daylight hours to illuminate the inner areas of a building, including areas that are not immediately adjacent to a window. This can decrease the amount of light required from artificial light sources. Daylighting can be used for such an approach, which involves admitting light from the sun and sky through windows, and redirecting that light towards the ceiling in areas of the room that are spaced from the windows.

A number of different daylighting films are available, which are typically applied to the interior surface of an existing window and/or are applied to the glass prior to installation of a windowpane. These materials can increase luminance deeper in the room by redirecting sunlight and/or diffusing light toward the ceiling plane. However, allowing more sunlight into a room in an uncontrolled manner may also increase the undesired glare due to the relatively large contrast in the intensity of the incoming light to the existing light in the room, or an uneven distribution of re-directed sunlight in the room. Generally, when the ratio in luminance between the object or task which is been viewed and the source light is greater than 10, glare may be perceived by human eyes.

Factors such as the angle between the task and the glare source, along with eye adaptation, can have significant impacts on the glare experienced by the eye. In cases where the glare is excessive, it may impair the vision of a person such that it is difficult or uncomfortable to look at certain objects. Such issues with glare can make an otherwise effective daylighting film undesirable for certain

applications. Thus, there is a need to provide an optical product for daylighting purposes that minimizes glare while effectively utilizing the maximum amount of incident sunlight throughout the day for lighting an interior area of building.

Summary

In one aspect of this invention, an optical product (e.g., an optical film) is provided that can redirect sunlight from a variety of angular directions into the deep interior of a room while minimizing glare. The use of natural light in this manner can reduce the required energy consumption for artificial lighting during the day and can also increase the productivity of building occupants, as is suggested by studies regarding worker productivity.

The light guiding members or films of the invention, which are also referred to herein as light redirecting members, generally improve three areas of light control, while also providing a desired aesthetic feature. In particular, the light guiding films described herein provide for increased glare control (i.e., minimized glare), provide for more diffuse light concentration on the ceiling, and minimize sensitivity of the light exiting angle to solar elevation. In addition, with regard to the clarity and translucent appearance of the film when applied to windows, the films of the present invention provide a highly reflective finish that enhances the aesthetics of the product.

In an embodiment of the invention, a light redirecting member is provided that includes a base layer and a plurality of optical elements extending from a first side of the base layer. At least one of the optical elements comprises a contoured lower surface with at least a portion that is reflective, and an upper surface spaced from the lower surface. The upper surface includes at least a first portion that is transmissive to incoming sunlight, and the lower surface is configured to reflect at least a portion of the incoming sunlight at multiple angles toward the upper surface. With this embodiment, the upper surface can further include a second portion adjacent to the first portion, wherein the second portion comprises a reflective material. Brief Description of the Drawings

The present invention will be further explained with reference to the appended Figures, wherein like structure is referred to by like numerals throughout the several views, and wherein:

Figure 1 is a side view of a portion of an embodiment of a light guiding film of the invention;

Figure 2 is a perspective view of a portion of an embodiment of a light guiding film of the invention;

Figure 3 is a schematic side view of one optical element or prism of a light guiding film of the invention, including exemplary incoming light rays;

Figure 4 is a schematic side view of the optical element of Figure 3, including an exemplary redirection of incoming light rays;

Figure 5 is a schematic side view of the optical element of Figure 3, including an illustration of the reflection of incoming light rays if the apex were configured as a sharp tip;

Figure 6 is a schematic side view of an optical element similar to that of Figure 3, with a portion of one of the surfaces having a slightly different contour to illustrate the reflection of incoming light rays;

Figure 7 is a schematic side view of the optical element of Figure 3, with a different contour to one of the surfaces illustrated in Figure 6 to illustrate the reflection of incoming light rays;

Figure 8 is a schematic side view of an optical element of the invention, including geometric parameters of one embodiment; and

Figure 9 is a schematic front view of a method of depositing material onto certain facets of the optical elements of a light guiding film of the invention.

Detailed Description

Referring now to the Figures, wherein the components are labeled with like numerals throughout the several Figures, and initially to Figures 1-3, one embodiment of a portion of a light guiding film of the invention is illustrated, with Figures 1 and 2 providing side and perspective views, respectively, and

Figure 3 providing a side view of one optical element of the light guiding film of Figures 1 and 2. In particular, light guiding film 10 generally includes a base layer 12 having a first surface 14, a second surface 16, and a plurality of extending optical elements or prisms 18 extending from the first surface 14 of base layer 12. That is, the base layer 12 includes a plurality of optical elements 18 extending from at least a portion of one side and has a relatively smooth surface on its other side.

The optical element 18 of Figure 3 includes a number of facets or surfaces. In particular, the element 18 includes a top surface 20, a bottom surface 22 spaced from the top surface 20 and configured such that it curves or converges toward top surface 20, and a truncated apex portion 24 extending between distal ends of the top and bottom surfaces 20, 22. Top surface 20 further includes a first portion 26 and a second portion 28 that extends at an angle from first portion 26. In accordance with the invention, bottom surface 22, apex portion 24, and second portion 28 of top surface 20 are all coated with a highly reflective coating. In accordance with the embodiments described herein, a highly reflective coating may be defined as a coating that can reflect greater than 90% of the incident light, and preferably greater than 95%, and more preferably greater than or equal to 99% of the incident light. The first portion 26 of top surface 20 is not coated with a reflective material, and therefore can admit incoming light, wherein exemplary light directed toward first portion 26 is represented by light rays 30.

Since the bottom surface 22 is curved and includes a highly reflective coating, no direct transmission of light can result from the incoming light that enters the optical element through the first portion 26. In this way, glare is minimized or eliminated. Thus, by properly designing the curvature and positioning of the bottom surface 22 relative to the top surface 20, all or most of the light rays that strike the bottom surface 22 will exit at a range of angles, all of which are in an upward direction. In this way, a more diffuse light spot will be created on the ceiling of the room. The overall light profile in the room is also less sensitive to the incident angle of sunlight than cases in which optical elements are not configured in this manner.

Referring also to Figure 4, the non-coated first portion 26 admits a portion of the incoming sunlight represented by light rays 30, which can enter from a number of directions. Other incoming light that hits the optical element in areas that are coated with reflective material will be rejected or reflected such that it does not enter the optical element. For example, light ray 32 shown in Figure 4 is representative of a light ray 30 that is directed to the apex portion 24, which is also coated with reflective material, and therefore does not enter the optical element 18 and is instead reflected downwardly and away from the light guiding film 10. The light rays 30 that are directed to the non-reflective first portion 26 will enter the optical element and are directed toward the reflective bottom surface 22. By limiting the incoming light using selective placement of highly reflective coatings and particularly designing the geometric shape and size of the bottom curved surface 22, the exiting directions of all of the admitted light can be controlled.

Figure 5 illustrates the optical element 18 described above, and includes a representation of a configuration in which the top surface 20 and the bottom surface 22 are extended to intersect at an apex 38 (as illustrated with broken lines). As shown, an incoming light ray 30 entering the optical element at the area of the top surface 20 closely adjacent to the apex 38 would be directed toward the area of the bottom surface 22 adjacent to the apex 38. This ray 30 then would reflect at an angle upwardly toward; top surface 20 of the optical element 18. Ray 30 would then reflect downwardly after hitting the upper surface 20 due to total internal reflection. That is, in an exemplary embodiment, the optical element 18 comprises a resin material with a refractive index of 1.49 such that when a light ray hits the inside of surface 20 at an angle of greater than 42.2 degrees, light will not be refracted at the surface, but will instead be reflected downwardly, as shown in Figure 5. The downwardly redirected light ray would cause some undesirable glare, which is minimized or eliminated with the truncated apex provided in the embodiment of Figure 3.

An additional feature of the optical elements 18 of the invention that minimizes glare is illustrated with respect to Figures 6 and 7, wherein Figure 6 includes a representation of a configuration in which the first and second portions 26, 28, respectively, are collinear and Figure 7 illustrates the optical element 18 as shown in Figure 3, with the second portion 28 angled slightly upward relative to the first portion 26. This angled relationship between first and second portions 26, 28 is designed to yield some portion of the reflected light and prevent or minimize the light that reflects downwardly. A comparison of Figures 6 and 7 demonstrates that the second portion 28 of Figure 6 is arranged such that the reflected light from incoming light ray 30 that enters the optical element 18 and hits the bottom surface 22 will then hit the second portion 28 and be deflected downwardly (i.e., in a direction that causes glare). In contrast, when the second portion 28 is arranged as shown in Figure 7, the reflected light from incoming light ray 30 that enters the optical element 18 and hits the bottom surface 22 will continue past the second portion 28 rather than hitting that surface and continue in an upward direction (i.e., in a direction that does not cause glare).

Figure 8 is a schematic side view of an optical element of the invention, including geometric parameters that determine the optics design to achieve the low glare performance described herein. In particular, an optical element 18 is shown with the following four horizontal reference lines: (1) reference line 50, which intersects the end of second portion 28 that is spaced from first portion 26; (2) reference line 52, which intersects the point where the first and second : portions 26, 28 of top surface 20 meet; (3) reference line 54, which intersects the : point where the first portion 26 of top surface 20 meets the truncated apex 24; and (4) reference line 56, which intersects the point where the bottom surface 22 meets the truncated apex 24.

Using reference line 50 as a baseline, the following three vertical measurements can be defined as follows: (1) Wc is the vertical distance between reference line 50 and reference line 52; (2) W_tis the vertical distance between reference line 50 and reference line 54; and (3) Wj, is the vertical distance between reference line 50 and the vertical position of an end 58 of bottom surface 22. Finally, a number of angular measurements are defined as follows: (1) a_c is the angular measurement between reference line 50 and second portion 28 of top surface 20 on the outside of the optical element 18; (2) a_t is the angular measurement between reference line 52 and the first portion 26 of the top surface 20 on the outside of the optical element 18; (3) _Γ is the angular measurement between reference line 56 and a reference line 60 that extends between the point where reference line 56 intersects with the truncated apex 24 and the end 58 of bottom surface 22; and (4) ot_a is the angular measurement between the surface of the truncated apex 54 and a reference line 62 that extends vertically from the point where reference line 54 intersects with the truncated apex 24.

With these established parameters, one embodiment of the invention includes an optical element 18 in which a number of relationships are present, which will minimize or eliminate glare when used in a light guiding film of the invention. Angle ct_c is greater than _t, and o¾ is greater than 7 degrees and less than 45 degrees. Angle a_ais less than 30 degrees, and o¾ is greater than 17 degrees. The ratio of Wc /W_b is preferably minimized to provide for maximum admitted daylight into the optical element without creating downward redirected or reflected light. The ratio of W_t/W is preferably less than ½ and greater than zero. Finally, the curvature of the bottom surface 22 is preferably designed in such a way that it can diverge reflected light in a range of angles, such as in a range of approximately 0 degrees to approximately 30 degrees. However, it is understood that adjustment of one or more of these parameters or ranges can affect the choice of other parameters in a particular configuration of the optical element 18 in order to achieve the desired results.

In accordance with the invention, the base layer of the light redirecting members can be made of the same material as the optical elements that extend from it, or the base layer and at least one of the optical elements can be made of different materials. The fabrication methods used for making the optical elements can include extrusion, embossing, UV curing, etching, patterning, gravure printing, and the like, although other manufacturing and fabrication techniques can additionally or alternatively be used.

Figure 9 is a schematic front view of a method of depositing material onto certain facets or surfaces of the optical elements of a light guiding film 10 of the invention. In accordance with this method, reflective coating material (e.g., a metalized coating) is directionally deposited on selected surfaces of the microstructures (i.e., optical elements 18) without the need to "block" or otherwise protect certain areas. That is, with the arrangement and configuration of optical elements 18 described herein, reflective material moving in a direction represented by arrows 70 will coat the bottom surface 22, the truncated apex 24, and the second portion 28 of top surface 20 of each of the optical elements 18. As shown, this is accomplished without the reflective material contacting the first portion 26 of the top surface 20 of the optical elements 18, since the various surfaces of the optical elements 18 are selectively coated using a deposition direction for the reflective material that is generally parallel to the surface that is to remain uncoated (i.e., first portion 26 of top surface 20). The coating process may be a highly directional coating method by which a metallic-like finish can be created, and may be performed at the end of a process of film patterning or performed in a separate operation.

The present invention has now been described with reference to several embodiments thereof. The entire disclosure of any patent or patent application identified herein is hereby incorporated by reference. The foregoing detailed description and examples have been given for clarity of understanding only. No unnecessary limitations are to be understood therefrom. It will be apparent to those skilled in the art that many changes can be made in the embodiments described without departing from the scope of the invention. Thus, the scope of the present invention should not be limited to the structures described herein, but only by the structures described by the language of the claims and the

equivalents of those structures.

Claims

Claims:

1. A light redirecting member comprising:

a base layer; and

a plurality of optical elements extending from a first side of the base layer, wherein at least one of the optical elements comprises:

a contoured lower surface that comprises at least a portion that is reflective; and

an upper surface spaced from the lower surface, the upper surface comprising at least a first portion that is transmissive to incoming sunlight; wherein the lower surface is configured to reflect at least a portion of the incoming sunlight at multiple angles toward the upper surface.

2. The light redirecting member of claim 1, wherein the upper surface further comprises a second portion adjacent to the first portion, wherein the second portion comprises a reflective material.

3. The light directional member of claim 2, further comprising a reference plane generally perpendicular to the first side of the base layer, wherein the first portion of the upper surface comprises a top external angle relative to the reference plane, and wherein the second portion of the upper surface comprises a second portion external angle that is greater than the top external angle.

4. The light redirecting member according to any of claims 1 -3, wherein the contoured lower surface comprises a convex outer surface.

5. The light redirecting member of claim 4, wherein the contoured lower surface comprises a partial-elliptically shaped surface.

6. The light redirecting member according to any of claims 1-5, wherein at least one of the optical elements further comprises a truncated apex portion extending between a first end of the contoured lower surface and a first end of the upper surface.

7. The light redirecting member of claim 6, wherein the truncated apex portion extends from the contoured lower surface to the first portion of the upper surface.

8. The light redirecting member of claim 6, wherein the truncated apex comprises a surface having an apex inclusion angle that is less than 30 degrees relative to a reference plane that is generally parallel to a first side of the base layer

9. The light redirecting member of claim 1 , further comprising a reference plane generally perpendicular to a first side of the base layer, wherein the first portion of the upper surface comprises a top external angle between 7 degrees and 45 degrees relative to the reference plane.

10. The light redirecting member according to any of claims 1-9, wherein the base layer is a film.

11;. The light redirecting member according to any of claims 1-10, wherein the base layer comprises a first material, and wherein at least one of the optical elements comprises a second material that is different from the first material.

12. The light redirecting member according to any of claims 1-10, wherein the base layer and at least one of the optical elements comprise the same material.

13. The light redirecting member according to any of claims 1-12, wherein the base layer further comprises a second side that is opposite from the first side and an attachment layer for attaching the second side of the base layer to a substrate.

14. The light redirecting member of claim 13, wherein the substrate is a window.

15. The light redirecting member according to any of claims 1-14, wherein the bottom surface comprises a curvature that diverges the upwardly reflected light in a range of approximately 0 to 30 degrees.