ENCAPSULATED MICROMIRRORS FOR LIGHT REDIRECTION

Abstract

A transparent polymer film for light redirection includes a carrier layer and a structured layer in optical contact with each other. The structured layer has a multitude of curved metallic micromirrors, which are parallel to each other and encapsulated in a transparent material and separated by a periodicity distance (p) of 10 to 1000 micrometer parallel to the film surface. 50% or more of the micromirrors’ surfaces have a cross section, perpendicular to the film surface, in the form of elliptic arcs, whose radii are from the range 5 p to 25 p, and the micromirrors are arranged in a depth (d) perpendicular to the film surface from the range 1.6 p to 3.0 p, especially 2 p to 2.5 p. Glazings can be equipped with the film.

Claims

1. A transparent polymer film comprising a carrier layer and a structured layer in optical contact with each other, wherein the structured layer comprises a multitude of curved metallic micromirrors, which are parallel to each other and encapsulated in a transparent material and separated by a periodicity distance (p) of 10 to 1000 micrometer parallel to the film surface, wherein 50% or more of the micromirrors’ surfaces have a cross section, perpendicular to the film surface, in the form of elliptic arcs, whose radii are from the range 5 p to 25 p, and the micromirrors are arranged in a depth (d) perpendicular to the film surface from the range 1.6 p to 3.0 p.

2. The transparent polymer film of claim 1, wherein 50% or more of the micromirrors’ surfaces, have a cross section, perpendicular to the film surface, in the form of circular arcs, whose radius is from the range 5 p to 25 p.

3. The transparent polymer film of claim 1 wherein the periodicity distance (p) is 10 to 500 micrometer, surface.

4. The transparent polymer film of claim 1, wherein the curved metallic micromirrors show a precision of the curvature, given as maximum deviation of the radius, of 5%, at maximum, and/or a maximum surface roughness of 150 nm.

5. The transparent polymer film of claim 1, wherein the curved metallic micromirrors extend over 80% or more of the length of the transparent polymer film in one dimension.

6. A glazing unit foreseen for mounting in a building or vehicle comprising two or more glass panes, wherein one surface of one pane is for facing towards the outside of said building or vehicle and one surface of another pane is for facing towards the inside of said building or vehicle, and further comprising the transparent polymer film of claim 1 in optical contact with one or two glass panes of said glazing unit, wherein the curved metallic micromirrors extend horizontally over 80% or more of the width of the one or two glass panes, and the transparent polymer film is arranged on the surface of the pane for facing towards the inside of said building, or is arranged on a surface facing another glass pane of said glazing unit.

7. The glazing unit of claim 6, wherein the micromirrors are substantially arranged with their concave surfaces facing upward and/or towards the inside, while their convex surfaces are facing downward and/or towards the outside, with the outside being the side of incoming sunlight and the inside being the side, which receives sunlight through the polymer film.

8. A multilayer glass comprising the transparent polymer film claim 1 laminated between two glass sheets.

9. A method for the preparation of a transparent polymer film comprising encapsulated curved metallic micromirrors, the method comprising: i) providing a vacuum deposition chamber with a metal evaporation source and a film support wherein the film support is straight over its length and bent, in the dimension perpendicular to its length, substantially in the form of a section of a logarithmic spiral, and wherein said film support is positioned in said deposition chamber with its concave side facing the metal evaporation source ii) providing a transparent polymer film comprising a substrate film covered by a structured layer of cured or partly cured transparent coating material, which structured layer comprises parallel grooves separated by periodicity distance (p) from the range 10 to 1000 micrometer; iii) positioning the transparent polymer film provided in step (ii) on the film support provided in step (i) with its structured layer facing the metal evaporation source and with main direction of grooves parallel to the film support’s length and iv) depositing metal from the evaporation source onto the film positioned in step (iii).

10. The method of claim 9, wherein (v) a transparent coating material curable by radiation is applied onto the structured side of the film obtained in step (iv), and (vi) the transparent coating material applied in step (v) is subsequently cured by applying suitable radiation.

11. The method of claim 10, wherein each of the transparent coating materials applied in steps (ii) and (v) is a UV curable coating material of refractive index from the range 1.4 to 1.7.

12. A method for the preparation of a glazing unit, the method comprising: providing a transparent polymer film produced according to the method of claim 9, coating a glass pane on one surface with a transparent coating material curable by radiation, arranging the transparent polymer film on said coated surface with its structured side contacting the wet coating material, and curing the transparent coating material by applying suitable radiation.

13. A metal vapor deposition device comprising a vacuum chamber equipped with a film support and a metal evaporation source positioned opposite to said film support, wherein the film support has a length and a width is bent in direction of its width substantially in the form of a section of a logarithmic spiral, with its concave side facing the metal evaporation source and wherein said film support can hold a film in the form of said section of the logarithmic spiral.

14. A rollable blind comprising the transparent polymer film of claim 1.

15. (canceled)

Description

BRIEF DESCRIPTION OF FIGURES

[0097] FIG. 1 gives a schematic overview over the process for preparing present redirecting polymer film: Using a suitable microstructuring tool (A), a UV curable coating on a suitable carrier film is structured and cured (step B). The structured layer thus obtained is subjected to metal vapour under an oblique angle (C). Subsequently, another resin layer is coated, which covers the metallic microplanes and fills the gaps between the structures to provide a smooth polymer surface (step D). Other than in present examples, this figure shows roller with grating perpendicular to the direction of imprinting (cross directional microengraving).

[0098] FIG. 2 shows the side view of the curved substrate holder (V2) with curvature along logaritmical spiral centered at the point of evaporation source (V1) mounted on a base plate (V3); the distances are: [0099] 560 mm (H1, vertical distance between base plate V3 and center of evaporation source V1); [0100] 139 mm (H2, vertical distance between base plate V3 and high end of sample holder V2); [0101] 25 mm (H3, vertical distance between base plate V3 and low end of sample holder V2); [0102] 158 mm (L1, horizontal distance between center of evaporation source V1 and low end of sample holder V2); [0103] 311 mm (L2, horizontal distance between high end and low end of sample holder V2).

[0104] FIG. 3 shows a perspective view of the curved substrate holder (V2) with one evaporation source (V1) mounted on a base plate (V3); the length of the evaporation source (L4) is 100.00 mm, the width (L5) of the substrate holder (V2) is 1010.00 mm.

[0105] FIG. 4a shows a perspective view on the evaporation process yielding present micromirrors; coating under oblique angle is achieved with the structured film arranged along a logarithmic spiral to obtain a constant impact angle for the aluminum evaporated from source V1 (located approximately at the spiral’s origin); the grooves of the structured film are arranged parallel to the length L5 of the sample holder.

[0106] FIG. 4b schematically shows a cross section of the metallised microstructures directly obtained in the present process as depicted in FIG. 4a forming present curved micromirrors on area 2; typically, the surfaces on present microstructures thus comprise grooves having a flat or rounded bottom (area 3); 2 lateral faces (areas 2 and 4), one thereof being curved (area 2, with its sections 2a, 2b and 2c forming the curved micromirror) while the other may be straight or rounded (area 4); and a top surface (area 1); while areas 3 and 4 obtain less or no metal coating, metal vapour is deposited in present process predominantly on areas 1 and 2, and may be mechanically removed from area 1 (polishing step).

[0107] FIG. 5 shows a schematic cross section of a double glazing comprising glass sheets 710 and 705 separated by air gap 706 mounted in a facade, with glass surfaces #1 to #4 and surface #1 facing outside the building, glass surface #4 facing inside the building, and glass surface #2 laminated with the present microstructured film (708, microstructuring indicated schematically only); 711 shows a possible light ray incoming from the outside and being redirected by present micromirrors in the film 708.

[0108] FIG. 6 shows the diamond tool comprising flat tip (T) of diameter (dt) of 8 micrometer, whose circular rounded side of radius (R) 500 micrometer deviates from the tool’s main axis (M) by 11.0° at the tip (angle indicated by dashed line), as used in present example to engrave a nickel phosphate plating on stainless steel roller.

[0109] FIG. 7 shows the logarithmic curvature of the sample holder (V2).

[0110] FIG. 8 shows cross sections of present redirecting film on glass interface #2 (according to the numbering explained for FIG. 5), mounted directly on glass G (variant (a) shown in the upper part of FIG. 8), or mounted on said interface #2 using an additional carrier layer C′ and adhesive A (variant (b) shown in the lower part of FIG. 8), and neighbouring the air gap between interfaces #2 and #3 on its other side. Enlargened sections on the right side of FIG. 8 show the film’s structuring with the carrier layer (in FIG. 8 denoted as Carrier Film) of thickness c (typically 0.05 - 0.2 mm), micromirrors M of thickness tm (typically 20 - 1000 nm), depth d (typically 0.04 - 0.5 mm) perpendicular to the film surface and height h (typically 0.05 d to 0.2 d), which micromirrors are curved with radius r (not shown in FIG. 8, r being typically from the range 5 p to 20 p) and separated by the periodicity distance p (preferably 0.02 - 0.2 mm) and encapsulated in polymeric binder E, with the total film thickness f (typically 0.1-1 mm).

[0111] FIG. 9 schematically shows the cross section of a part of present transparent polymer film comprising the encapsulating binder (E) with one circular micromirror (M), whose length is defined by its height (h) and depth (d), and whose positioning is indicated by the centre of the circular curvature (x) and the tangents on both ends of the circular section forming an angle beta (ß) at the end facing towards the inside of the room and an angle alpha (α) at the end facing the side with incoming sunlight, each with the (polymer film’s surface) plane normal (N), where alpha > beta.

[0112] FIG. 10 schematically shows windows (or blinds) equipped with present transparent polymer film indicating the orientation of present micromirrors. X denoting horizontal direction and Y denoting vertical direction. FIG. 10a shows a typical orientation of the linear metallic micromirrors extending horizontally. In windows orientated towards the east, the film may be mounted with a clockwise rotation as shown in FIG. 10c, and in windows oriented towards the west, with a counter clockwise rotation (FIG. 10d). For other orientations, the micromirrors may follow a wave pattern instead of a line pattern (FIG. 10b).

EXAMPLE 1: MODELLING

[0058] The base setting for the simulation is as follows: [0059] A south oriented room 5 m wide and 8 m deep with a ceiling height of 3 m; [0060] the low 1 m of one façade is opaque and the remaining 2 m are glazed; [0061] the glazed surface is split in two with a view section from 1 m to 2 m height and a daylighting section from 2 m to 3 m.

[0062] The view section is equipped with a double glazed IGU, which is purely insulating (WSG), or provides additionally a sun protective function (SSG). A daylight redirecting element cannot be placed in this section as it could induce glare to the occupant after redirection. The WSG has a visible transmission of 80% and a solar heat gain coefficient (in the following also referred to as g value / SHGC) of 63%. The SSG window has a visible transition of 40% and a solar heat gain coefficient (g value / SHGC) of 23%.

[0063] The daylight section is fitted with SSG or WSG as reference cases and with various DRF film solutions to compare performance. The comparative film (“prismatic” film further noted in the below example 3) comprises prismatic redirecting elements as shown in FIGS. 4 and 7 of US-2018-095196, but with slightly amended dimensions noted in the below table A (dimensions measured from film as purchased from 3 M).

TABLE-US-00002 Structure of prismatic film simulated compared to film shown in FIG. 7 of US-2018-095196 (A-E given in micrometer) A B C D E a b prismatic simulated 40 48 9 12 49 22° 8° US-2018-095196 (FIG. 7 ) 50 64 14 16 72 10.5° 17°

[0064] The room has no other side window. In all cases an indoor rollable white blind with a diffuse transmittance of 10% is used for glare protection. The blind is rolled down when the luminance exceeds 3000 cd/m2 for an occupant. The room is modeled with a reflectivity of 70% for ceilings, 50% for walls and 20% for the floor. Artificial light is provided by a dimmable LED light adapting the LED output to provide 500 lux on the work plane. A mixed strategy with 80% direct and 20% indirect artificial light is used to maximize user comfort. The LED is modelled with a final efficiency of 100 Im/ W (including dimmer, power adapter etc.).

[0065] The window systems are modeled in the Window7 software from Lawrence Berkeley National Laboratory (LBNL) combining a simulated bidirectional transmission distribution function (BTDF) for the DRF film using the standard Klems subdivision of the hemisphere into 145 patches with existing glazing from the database. The BTDFs of DRFs are simulated in Radiance using the genbsdf function using a geometrical model. A textile blind is added to model situation in which the solar protection is drawn down. The resulting combined BTDF for g value and visible transmittance is used in a Radiance simulation to compute hourly illuminance values at workplane height within the room as well as luminance for occupants to decide on the blind usage.

[0066] For the thermal simulations, the following criteria are used: adiabatic boundary to neighboring offices, U value for the wall 0.25 W m.sup.-2 K.sup.-1, medium thermal mass (inner heat storage capacity: 165 kJ/m2K), efficient ventilation (air change rate of 0.22/h) and window night cooling with an air change rate of 1.5/h in summer, 0.38/h in winter (with a switching temperature of 24° C. for the activation of night cooling), controlled indoor temperature range of 21° C. - 26° C. with active cooling and heating at a coefficient of performance (COP) of 3.5 for cooling and 3 for heating. The COP is a ratio of useful heating or cooling provided to work, internal loads are set at 9.52 W/m.sup.2 to account for heat generated by appliances and occupants.

[0067] The performance criteria are daylight autonomy and final primary energy usage (using a factor 2.6 to convert from the energy required on site to the building’s effective consumption of primary energy). In particular, the daylight autonomy in the depth of the room is taken as key performance indicator.

EXAMPLE 2: PREPARATION OF A LIGHT REDIRECTING FILM LAMINATED ON GLASS

[0068] A diamond tool as shown in FIG. 6 is prepared with a total cutting height of 100 micrometer (in main tool direction M), it has a convex curvature of 500 micrometre radius (R) on one side (thus forming a circular arc), and a flat part tilted by 12° from the tool main direction (M) on the other side. The tip of the tool (T) is a flat of 8 micrometer cross section (t), perpendicular to the tool main direction (M). The side with a convex curvature starts with an angle of 11° relatively to main direction (at tool tip) therefore it has a total included angle of 23°. The curvature of this side of the tool stops when it reaches 0° to avoid undercut during machining.

[0069] The tool is used to engrave a nickel phosphate plating on stainless steel roller with diameter of 200 mm and width of 500 mm. The roller is machined on an ultra-high precision turning lath such as the Nanotech HDL 2600 by Moore Nanotechnology systems. The diamond tool is plunged at 72 mu depth. The grooves are realized along the roller surface, nearly in the plane perpendicular to the roller axis. Successive grooves are parallel but slightly tilted with respect to this plane in order to shift the tool by exactly 40 mu at each revolution of the tool and realize a thread like a continuous groove around the roller. The spacing between grooves (periodicity) is therefore 40 micrometre. Total machined width is 325 mm.

[0070] The obtained roller is used for ultraviolet micro imprinting lithography using a UV crosslinking lacquer (Lumogen® OVD Primer 301; BASF) on a PET substrate in a roll to roll setup. The PET substrate is a 125 mu thick and 580 mm wide Hostaphan® GN 125.0 CT01B film pre-treated for optimal adhesion (Mitsubishi Polymer Film GmbH). A continuous, approximately 50 m long, cured structured film is obtained and wound up in this roll to roll replication process.

[0071] Sample sheets thus structured and cured are cut down to a suitable size of 348×1000 mm.

[0072] Sample sheets are placed on a curved substrate holder (V2, see FIG. 2 (side view) and 3 (perspective view showing only one evaporation source). The substrate holder (V2) is curved along a logarithmic spiral centered on the evaporation sources and for the angle corresponding to desired shading (ß = 18.5° for present sample; see FIG. 7). A logarithmic spiral is a curve with equation r = a e.sup.(θ/tan ϕ) in polar coordinates (r, 6). It has the particularity that at any point (P) of the curve, the angle ϕ between the radial line (r; line from the origin O to P) and the tangent (t) to the curve in P is constant. a is the distance between the origin O of the spiral and the spiral at 6 = 0. For preparing the present sample, this distance (a) is set to be 300 mm, ϕ = 71.5° and θ = 0° at the horizontal. The angle between the radial line (r) and the normal (n) to the sample is therefore constant and equal to 18.5°. The section of the spiral used to define the sample holder surface is between 68.6° and 107.1°. The black curve in the upper section of FIG. 7 shows the curvature of the present sample holder (V2).

[0073] The mounted sample is placed in a vacuum physical vapor deposition chamber equipped with 6 evaporation sources placed symmetrically on both sides at 200 mm, 350 mm and 490 mm distance from the centre and above the sample and positioned as described for FIG. 2 below. Aluminum is evaporated from the sources each comprising a set of tungsten coils of 100 mm length and 15 mm diameter positioned as described for FIG. 2 and located in regular distances over the sample sheet to obtain a homogenous distribution of coating thickness. After loading the coil with 99.99% pure aluminum wires, the coil is heated by Joule heating until evaporation temperature. The process is run at a pressure of 2 × 10.sup.-4 mbar Alternatively, the process can be run at lower pressures to improve angular accuracy (e.g. down to 1 × 10.sup.-6 mbar); to compensate for diffusion of aluminium atoms at 2 × 10.sup.-4 mbar, the sample holder was tilted by elevating the higher edge of the sample holder by 30 mm.

[0074] A sample of metallized film thus obtained is investigated for the metal thickness on structure areas as identified in present FIG. 4b; results are compiled in the below table B.

TABLE-US-00003 Thickness of aluminum layer on structure Area on film structure (FIG. 4b) Thickness (nm) 1 (top) 109 2a (deeper end of micromirror) 83 2b (center of micromirror) 64 2c (front end of micromirror) 50 3 (groove, flat snapped-off part) 45 4 (structure’s flat back side) < 5 (not detectable)

[0075] Two of the resulting sheets with metallic coating are polished using a an eccentric polisher with a grain 4000 disk (Abralon™ 4000, Mirka) and subsequentially washed by passing them in two successive ultrasonicated, deionized water tanks and dried with hot air. This removes the coating in position 1.

[0076] The sheets are then assembled with transparent adhesive tape after cutting them down to 323 ×984mm to remove unstructured areas and side effects. This 646 ×984mm film is then fitted to a clear glass pane of slightly larger dimension (676×1014 mm) next to each other to cover most of the surface. The adhesion of the film is obtained by applying the same UV lacquer as in the microstructuring step described above between sheets and glass pane and curing by UV light. The glass is precoated with 400 mu thick liquid lacquer and the coated film is applied manually with the structured and coated side facing the glass. To avoid liquid lacquer to escape, a strip of hot-melt adhesive is applied on the edges to seal the film to the glass and to contain the liquid lacquer. The glass is placed on a cold metal plate (-14 to -18° C.). UV light source is used to cure the lacquer. Hereby the structure is encapsulated and fitted onto glass simultaneously, using the same UV lacquer as described above.

[0077] Subsequently, the transparent adhesive tape is removed and a transparent 1 mm thick PET plate is laminated on top of the structured film substrate. This is performed using the same liquid lacquer to remove any unevenness of the film surface and construct two perfectly parallel surfaces (air-glass interface and PET-air interface). The final stack is therefore: 1 mm PET plate, 10-300 mu cured UV lacquer, 125 mu PET film, 100-1000 mu cured UV lacquer stack with encapsulated mirrors, 4 mm glass.

[0078] The glass pane carrying the sheet thus microstructured and coated is mounted inside a double glazing, with the film comprising the encapsulated mirrors on interface # 2 (counting from the outside, see FIG. 5).

EXAMPLE 3: MEASUREMENT OF PROTOTYPE

[0079] DIN A4 sized samples resulting from the preparation described in Example 2 are measured for characterisation.

[0080] Complex optical devices used in building facades are sometimes named Complex or Advanced Fenestration System (CFS or AFS) and are characterized by a bidirectional scattering distribution function (BSDF) and in particular the bidirectional transmission distribution function (BTDF) which influences the resulting performance on the inside of a building. This BSDF can be analytical or empirical. For complex behaviours, an empirical function can be measured using a goniophotometer to generate a matrix describing the relation between an incident direction and the resulting distribution in reflection and transmission. For visualisation the matrix is generally divided in four matrices: two for each side of the sample (front and back): one for the transmission distribution and one for reflection distribution. Therefor a goniophotometer is generally composed of a light source and a light sensor. The light source is generally collimated to measure the response of the sample at a singe incident angle. The source or the sample is generally mobile to measure a set of incident directions changing both the elevation angle (angle to the normal of the sample) and the azimuth angle (angle to the vertical plane containing the surface normal). The sensor can be a camera to measure an intensity map of reflected and transmitted distributions of light or a photoreceptor to measure the intensity in an individual reflection or transmission direction.

[0081] The DRF film of present invention is measured under 270 incident directions. The incident direction corresponds to the 145 zones of the hemisphere defined by Klems on both sides of the sample, according to CFSstandard. The used goniophotometer measures up to 100.000 directions in transmission and reflection individually, adapting the point density depending on the variability of the measured signal. This guarantees to detect very narrow peaks within the hemisphere without a very fine, full scanning. The data points aree taken with a photodetector and using a filter to account only for the visible light, and take into account the sensitivity of the human eye during the daytime (according to the photopic v-lambda curve). The large set of data points measured with this technique is then used to generate a simplified model for simulation by agglomerating measurement points into the same 145 zones in transmission and 145 in reflection. This facilitates the visualisation and enables annual simulations following the three or five phase method described by Andy Mc Neil. The extensive data set is also used to generate a more precise so-called tensor tree model for simulation of single scenes with a defined sky, this representation captures detailed peaks and is suited for a precise characterisation of glare or sun patches for example. Those models are obtained in an xml formatted file using the Radiance programmes pabobto2bsdf and bsdf2klems for the Klems representation or pabobto2bsdf and bsdf2ttree for the tensor tree representation. Both can then be viewed using the BSFDViewer software from LBNL. As described in Example 1, the Klems model can be used in the Window 7 programme to combine the measured DRF with existing glazing and assemble double or triple insulating units for example. The resulting glazing is also defined by a BSDF model that can then be used in other simulation tools.

[0082] Two samples are measured. The first sample is obtained as described in Example 2 but using only a single evaporation source placed above a sample covering only 210 mm of the 1000 mm sample holder size. The deposition is performed in three successive rounds at a pressure of 8 10.sup.-4 mbar and without polishing. All other steps except the assembly of two pieces are performed as described to fit a 210 mm by 180 mm film onto an A4 sized glass.

[0083] The second sample is obtained as described in Example 2 but using only a single evaporation source placed above a sample covering only 210 mm of the 1000 mm sample holder size. The deposition is performed in three successive rounds at a pressure of 2 10.sup.-4 mbar. All other steps, including polishing but excluding assembly of two pieces are performed as described in Example 2 to fit a 210 mm by 180 mm film onto an A4 sized glass.

TABLE-US-00004 The following table illustrates some key numbers regarding these two samples taken from this larger set of measured data ALL VALUE FOR FRONT SIDE Sample 1 Sample 2 at 0° incidence Transmittance total 41.3 % 62.5% Transmittance direct 33.96 % 43.1% Max transmitted redirected peak (and angle of peak) 2.75 % (-20°) 6.2% (-10°) at 20° incidence Transmittance total 63.2 % 64.1 % Transmittance direct 60.1 % 47.6 % Max transmitted redirected peak (and angle of peak) 0.6% (-30°) 3.3 % (-10°) at 40° incidence Transmittance total 50.1% 55.7 % Transmittance direct 30.1% 15.5 % Max transmitted redirected peak (and angle of peak) 8.7 % (+20°) 10.6 % (+20°) at 60° incidence Transmittance total 41.0 % 43.5 % Transmittance direct 3.4 % 1.1 % Max transmitted redirected peak (and angle of peak) 26.3 % (+40°) 20.2% (+40°)

[0084] The first column in the abobe table C indicates the angle of incidence for which the transmission distribution function was measured. All the presented measurements are taken on the front side and for a positive elevation angle i.e. from the upper side. The incident light is in the vertical plan perpendicular (azimuth = 0) to the sample and the angle measured between normal to the sample and light source position, positive angles are for upward direction. “Transmittance total” is the total transmittance of the sample for the given angle. Transmittance is the fraction of transmitted radiation with respect to the incident radiation. “Transmittance direct” is the transmittance in the same direction as the incident light or with a very slight deviation (less than 5° in elevation and azimuth angle). Finally, “Max transmitted redirected peak” is the largest of the 144 transmittances in a direction different from the incident direction. For those values, the corresponding angle of redirection is given, negative for downwards, positive for upwards. The angle is given in the vertical plane, perpendicular to the sample and measured relative to sample normal. The “Transmittance direct” and “Max transmitted redirected peak” values are absolute, not relative to the first.

EXAMPLE 4: COMPARISON OF DESIGN WITH EXISTING PRODUCT

[0085] The DRF film of present invention as described in Example 2 but with a diamond turning depth of 80 mu instead of 72 mu and an ideal configuration with mirrors only on part 2 and with an ideal perfectly specular reflectance of 95% mirrors is modeled geometrically in the Radiance format and the Radiance program genbsdf was used to simulate a BTDF in Klems format with four 145×145 matrices (FILM_SIM).

[0086] A commercially available sample of a daylight redirecting film is measured as described in Example 3 to form a similar BTDF in Klems format with four 145×145 matrices (FILM_comp).

[0087] The following tables present daylighting performances simulated for two different glare protection concepts for a building at Torino (IT) following the method described in Example 1. A state of the art IGU with solar protection coating is taken from the glass data base of Window 7 and is used as reference. It has a transmittance of 40% in the visible range and 23% solar heat gain coefficient at normal incidence (SSG_4023). Using Window 7 software, an identical window is combined once with the simulated film FILM_SIM on interface #2 (DEMO) and once with the measured FILM_comp on interface #2 (comp).

[0088] The following table 1 contains results obtained for the above comparative glazing unit, and for the two present glazing assembly. The simulation is performed as described in Example 1 and yields results for a statistical year with hourly resolution. Generally, to manage glare, a blind strategy is put in place, using glare protection blinds or roller shadings. In the present case an indoor rollable white blind with a diffuse transmittance of 10% is used for glare protection. The blind is rolled down when the luminance exceeds 3000 cd/m2 for an occupant.

[0089] Along the year two different glare management strategies are used to perform this comparison for the location at Torino (IT) with a south orientation: [0090] In winter when the sun is low, the blind is used in both the view section (bottom window) and daylight section (upper window) [0091] In summer when the sun is high, the blinds are used only in the view section. The daylight section always remains unshaded

[0092] Table 1 shows the results for a SSG 40/23 glazing comprising a light redirecting film according to the invention (DEMO) or the commercial film (comp) in the upper area (daylighting section); for further comparison purposes, results are shown for a glazing without DRF (SSG_4023).

TABLE-US-00005 Energy used kWh/m2 per year, daylight autonomy and hours with glare; no glare protection roller in summer Primary energy needs kWh/m2 per year Daylight autonomy room depth Office hours where luminance is exceeded for occupants during summer Cooling Heating Lighting TOTAL SSG_4023 12.7 1.1 14.9 28.7 51.1% 32.9% DEMO 12.8 1.1 15.1 29.0 50.2% 7.1% comp 12.2 1.1 16.1 29.4 45.4% 10.0%

[0093] It is apparent that by using the DRF of present invention, daylight autonomy can be very high while the risk of glare is kept under control: The number of office hours during the year, where luminance is exceeded, remains below 5%.

[0094] In a situation where glare occurs, the blinds are typically closed and the daylight potential is therefore lost. With the present DRF, the usage of blinds can be avoided in summer, therefore inducing energetic savings.

[0095] A further simulation of the same situation, but with the use of blinds in summer also in the daylighting part, the use of SSG_4023 glazing in the daylighting section results in 31.7% daylight autonomy in room depth, 0% office hours with glare risk but with a resulting total energy need of 34.9 kWh/m2 per year (increase of 21.6% in energy needs with respect to the situation presented in table 1).

[0096] Several location are investigated and several building types modeled. The present DRF shows a significant improvent of daylight autonomy in all cases.