FIELD OF THE INVENTION

The present invention generally relates to a patterned glass and a method for making the same. More particularly, the present invention relates to a patterned glass and a method for optimizing the patterned glass, the patterned glass having maximized glare mitigation and improved visual comfort to the customer/end-user.

BACKGROUND

Patterned glasses have one of their surfaces feature a design created by screen printing or other relevant printing techniques. Patterned glasses are clear, coated or tinted glasses printed with ceramic ink designs and subsequently heat treated. Varied patterned glasses and designs that fully or partially cover the surface of the glass are available in the market, and find application in doors, bus shelters, telephone kiosks, display signs etc., in addition to the conventional applications such as wall partitions, wall cladding, curtain walling and facades. These products combine aesthetics and functional performance for use in partitions, roof glazing and external walls. They can provide dramatic decorative effects or simple designs for privacy, glare mitigation and solar control.

Specifically, facade glass for buildings have constantly evolved in the last few decades with new products in the market featuring enhanced safety, energy efficiency and aesthetics. Incorporating a design pattern on a facade glass has not only been a practice gaining traction amongst architects to provide a distinct identity to a building, but also to mitigate glare. Existing state of art has developed several methods to reduce glare.

US20100246016A1 describes a method of making a glass article with an anti-glare surface by growing crystals on its surface and etching the glass surface surrounding the crystals to form a roughened texture resulting in an anti-glare surface. EP2563733B1 describes a method of surface texturing to reduce specular reflection and US20110062849A1 describes a glass article that is ion exchangeable and has at least one roughened surface showing anti-glare properties. The glare referred in these patents is the reflection from the surface, i.e., specular reflection from the surface has been taken as a measure of glare.

US20030211337A1, EP1165454A and US6753056B1 in general describe a decorative film for glass-paned windows for privacy protection, light screening property and decorative effect. The decorative film comprises a transparent substrate and a colored layer comprising ink containing an optical coherent pigment.

US5415731A describes a method of preparing a non-glare glass that has a number of fine, transparent, etched patterns on its surface, and thus, can scatter light applied to the surface in a random manner, resulting in a non-glare surface.

US4944986A describes a low reflectance glass surface which includes a particular combination of surface structures which produce a low reflectance yet a high clarity glass. US3895859A describes a glare-reducing window comprising a glass pane having opaque coatings uniformly distributed throughout a desired area of the glass, a window frame and an opaque film formed along the periphery of the glass pane. This document does not teach about glare measurement or optimization. Light transmittance is measured and a reduction in light transmittance is assumed to be reduction in glare, however this is not always true. Recently developed glare measurement methods have not been implemented for optimization.

US3249752A describes a glare reducing refractor for concentrating an emission of light within the refractor between pre-selected vertical angles and using prismatic formations for reducing glare.

The aforementioned state of art includes patents on methods developed to reduce glare: (1) by surface texturing of the glass or growth of small structures on the glass surface; (2) by means of anti-reflective coatings; (3) by means of providing opaque coatings on the glass surface. Notwithstanding all the past experience and technology available for making a non-glare glass substrate, there exists no method for obtaining a glass substrate having an optimized pattern shape or pattern coverage that provides maximized glare reduction for visual comfort. Further, some of the prior art have measured a reduction in light transmission as a result of the having patterns/opaque coatings on the glass surface. However, in all the disclosed state of art, the reduction in glare has never been evaluated and quantified nor has the geometry of pattern been optimized for minimizing the glare. Most of these are based on an assumption that patterns/ opaque coatings on glass will reduce glare by blocking the light.

Existing literature assumes that patterns and frits reduce glare by blocking the light. However, the research studies performed by the present applicant has shown that the edges of patterns can cause visual discomfort/glare by scattering of the light. Therefore, it is necessary to ensure that the glare reduction that is caused by cutting down the light transmission exceeds the glare aggravation caused by the scattering of light along the pattern edges.

Thus there is a need in the art for providing a patterned glass substrate for both interior and exterior applications having maximized glare mitigation. The present invention proposes such glass substrates and further addresses the drawbacks associated with the prior art.

OBJECT OF THE INVENTION

The object of the present invention is to provide a patterned glass having maximum glare mitigation and improved visual comfort by ensuring that glare mitigation by cutting down the light transmission, is greater than glare aggravation due the scattering of light along the pattern edges.

Another object of the present invention is to provide a method for making a patterned glass substrate, such that the pattern provided on the glass substrate acts as a means to cut down on light transmission, decrease glare aggravation due to light scattering and reduce the discomfort from glare spots, thereby improving visual comfort.

Yet another object of the present invention is to provide a method for optimizing a patterned glass substrate in order to obtain a maximized glare mitigation, which ensures that the decorative patterns provided on the glass substrate cut down on light transmission, in a way such that glare mitigation is greater than glare aggravation, thereby improving visual comfort.

SUMMARY OF THE INVENTION

In an aspect, the present invention provides a patterned glass with maximum glare mitigation under direct and diffused light. The patterned glass comprises a transparent glass substrate; and a decorative layer on one side of the transparent substrate’s surface applied in a predefined geometrical pattern. The geometrical pattern has an optimized area to perimeter ratio per unit pattern across a predetermined pattern area coverage. The optimized area to perimeter ratio per unit pattern and the pattern area coverage ensures that glare mitigation by cutting down light transmission, is greater than glare aggravation due to light scattering along the edges of the predefined geometrical pattern.

In another aspect, the present invention provides a method for making a patterned glass substrate having maximized glare mitigation under direct and diffused light. The method comprises the steps of, providing a clean and dried transparent substrate, applying a decorative layer in a predefined geometrical pattern having an optimized area to perimeter ratio of a unit pattern across a predetermined pattern area coverage, on a surface of the transparent substrate. The optimized area to perimeter ratio of per unit pattern and the pattern area coverage ensure the glare mitigation by cutting down light transmission is greater than glare aggravation due to scattering of light along the pattern edges.

In yet another aspect, the present invention provides a method for optimizing a patterned glass substrate in order to obtain a maximized glare mitigation under direct and diffused light. The method comprises the steps of, determining glare conditions of a non-patterned transparent glass substrate in terms of daylight glare probability (DGP), determining total area of the glass substrate intended to be provided with a decorative layer in the form of a geometrical pattern, determining a desired percentage of glare mitigation and/or visual light transmission, determining area to perimeter ratio and pattern area coverage based on the percentage of glare mitigation and/or visual light transmission, determining a suitable geometrical pattern for obtaining the desired glare mitigation and visual light transmission, along with the determined area to perimeter ratio and pattern area coverage, and providing the suitable geometrical pattern on the determined area of the glass substrate. The geometrical pattern provided on the glass substrate ensures that the glare mitigation by cutting down light transmission is greater than glare aggravation due to scattering of light along the pattern edges.

The other features of the present invention will be described in detail in conjunction with the accompanying drawings and the specific embodiments, but not limit the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention can be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings.

FIG. la, lb illustrates a schematic representation of the line patterned, circle patterned designs on a glass substrate according to one embodiment of the present disclosure.

FIG. lc, Id, illustrates a luminance maps of the hole patterned and gradient hole patterned designs on a glass substrate according to one embodiment of the present disclosure.

FIG. 2 illustrates a luminance maps of the line patterned, circle patterned designs on a glass substrate according to one embodiment of the present disclosure.

FIG. 3 illustrates a graphical representation of percentage reduction in glare with respect to A/P ratios of Circles vs. Line patterns on a glass substrate compared at two different patter area coverage according to one embodiment of the present disclosure.

FIG. 4 illustrates a graphical representation of percentage decrease in glare as a function of different area/perimeter ratios for the same pattern coverage area (circles and lines) on a glass substrate according to one embodiment of the present disclosure.

FIG. 5 illustrates a graphical representation of percentage reduction in glare with respect to the pattern area coverage of the patterns on a transparent substrate according to one embodiment of the present disclosure.

FIG. 6 illustrate a graphical representation of the luminance intensity profile across a 2D cross section of a line pattern according to one embodiment of the present disclosure.

FIG. 7 illustrates a set up used for measuring vertical eye illuminance for the hole patterned, gradient hole patterned and abstract shape patterned according to one embodiment of the present disclosure.

FIG. 8 illustrates a graphical representation indicating the trend of DGP with respect to the %VLT for a non-patterned sample according to one embodiment of the present disclosure. FIG. 9 a illustrates a graphical representation indicating the area average luminance, vertical eye luminance against the coverage density for a patterned sample according to one embodiment of the present disclosure.

FIG. 9b illustrates a graphical representation indicating the DGP against the coverage density for a patterned sample according to one embodiment of the present disclosure.

FIG. 10 illustrates the luminous intensity along the hole patterned edges of the patterned sample according to one embodiment of the present disclosure.

FIG. 11 illustrates the luminous intensity along the gradient hole patterned edges across a row of holes of the patterned sample according to one embodiment of the present disclosure.

FIG. 12 a, 12b illustrates a luminance maps of the white and black patterned circle designs on a glass substrate, to show the influence of color on edges of the pattern according to one embodiment of the present disclosure.

FIG. 13 a, 13b illustrates a graphical representation indicating the glare measurement for white and black patterned circle patterned sample according to one embodiment of the present disclosure.

Skilled artisans appreciate that elements in the drawings are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the disclosure.

DETAILED DESCRIPTION

The following description, in combination with the figures, is provided to assist in understanding the teachings disclosed herein. The following discussion will focus on specific implementations and embodiments of the teachings. This discussion is provided to assist in describing the teachings and should not be interpreted as a limitation on the scope or applicability of the teachings.

Note that not all of the activities described in the general description or the examples are required, that a portion of a specific activity may not be required, and that one or more further activities may be performed in addition to those described. Still further, the order in which activities are listed is not necessarily the order in which they are performed.

The specification and illustrations of the embodiments described herein are intended to provide a general understanding of the structure of the various embodiments. The specification and illustrations are not intended to serve as an exhaustive and comprehensive description of all of the elements and features of systems that use the structures or methods described herein. Certain features, that are for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in a sub combination. Further, reference to values stated in ranges includes each and every value within that range. It will further be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications in the disclosed composition, system, product and method, and such further applications of the principles of the disclosure therein being contemplated as would normally occur to one skilled in the art to which the disclosure relates.

The description in combination with the figures is provided to assist in understanding the teachings disclosed herein, is provided to assist in describing the teachings, and should not be interpreted as a limitation on the scope or applicability of the teachings.

As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a method, article, or apparatus that comprises a list of features is not necessarily limited only to those features but may include other features not expressly listed or inherent to such method, article, or apparatus. Further, unless expressly stated to the contrary, "or" refers to an inclusive-or and not to an exclusive-or.

The use of "a" or "an" is employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one and the singular also includes the plural, or vice versa, unless it is clear that it is meant otherwise. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The materials, methods, and examples are illustrative only and not intended to be limiting. To the extent that certain details regarding specific materials and processing acts are not described, such details may include conventional approaches, which may be found in reference books and other sources within the manufacturing arts.

Reference throughout this specification to “one embodiment” “an embodiment” “some embodiments” “alternate embodiment” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of such phrases throughout this specification may, but do not necessarily, all refer to the same embodiment.

The term "patterned glass substrate" as used herein relates to a glass substrate having a predefined decorative pattern and improved functionalities such as glare reduction, solar control and desired visual light transmission created by a combination of several steps of arriving at a method of making and optimizing such a patterned transparent substrate.

The term “pattern” as used herein refers to any decoration created on the surface of the glass substrate by applying a decorative layer in any form applied using any printing technique and having a predefined geometry.

The term “decorative layer” as used herein refers to layer of coating provided on the glass substrate using an enamel, lacquer or ink or a combination thereof.

The term “non-patterned glass substrate” as used herein refers to a counterpart of the glass substrate as used in inventive examples, without a pattern on the glass substrate, i.e., a bare glass.

The main aspect of the present invention is to provide a patterned glass with maximum glare mitigation under direct and diffused light. The patterned glass in accordance with the present disclosure comprises a transparent glass substrate. One side of the transparent glass substrate’s surface is provided with a decorative layer applied in a predefined geometrical pattern. The predefined geometrical pattern in accordance with the present disclosure has an optimized area to perimeter ratio per unit pattern across a predetermined pattern area coverage. In accordance with the present disclosure the optimized area to perimeter ratio per unit pattern is obtained by mapping percentage glare mitigation and percentage visual light transmission across a range of geometrical patterns.

In the present disclosure the critical parameters such as area to perimeter ratio, pattern area coverage, percentage glare mitigation, and percentage visual light transmission have been tailored to maximize the glare mitigation for a patterned glass substrate under direct and diffused light. The net effect of a given pattern on glare depends on the precise engineering of the geometry of the pattern.

In an embodiment the predefined geometrical pattern is obtained by calculating percentage glare mitigation across a range of area to perimeter ratio and a range of area coverage of desired geometrical patterns. The glare mitigation percentage is normalized against the glare mitigation percentage of a non-patterned transparent glass substrate.

In an embodiment the percentage glare mitigation of the patterned glass substrate is calculated by the change in daylight glare probability (DGP) of the patterned glass with respect to the daylight glare probability of a non-patterned glass.

In accordance with the present disclosure the pattern provided in the form of a decorative layer, is selected from a group including but not limited to lines, circles, square, triangle, oval, rectangle, octagon, parallelogram, trapezoid, pentagon, hexagon, stars, gradients, abstract shapes or a combination thereof.

In accordance with the present disclosure the decorative layer material which is used for providing the pattern is selected from a group including but not limited to enamel, lacquer, inks or a combination thereof.

In an embodiment the area to perimeter ratio for defined geometrical patterns such as lines, circles, square, triangle, oval, rectangle, octagon, parallelogram, trapezoid, pentagon, hexagon is achieved by using a standard formulae corresponding to the geometric pattern. In another embodiment the area to perimeter ratio for stars, gradients or any such abstract shapes is obtained by image analysis algorithm.

Similarly, the pattern area coverage for defined geometrical patterns such as lines, circles, square, triangle, oval, rectangle, octagon, parallelogram, trapezoid, pentagon, hexagon is obtained by using a standard formulae corresponding to the geometric pattern. In another embodiment the pattern area coverage for stars, gradients or any such abstract shapes is obtained by image analysis algorithm.

The glass substrate in accordance with the present disclosure onto which the predefined geometrical pattern is provided, is selected from a group including but not limited to coated substrate, clear substrate, inorganic silica substrate, organic transparent substrate, tinted substrate. In a preferred embodiment the glass substrate is selected from coated or clear substrate. In another preferred embodiment the glass substrate is a functionally coated solar control glass.

The thickness of the decorative layer in accordance with the present disclosure is in the range of 1 to 40 pm. In a preferred embodiment the thickness of the decorative layer is in the range of 5 to 20 pm. In some embodiments of the present disclosure, higher pattern thickness and increased use of frits and/or pigments in the decorative layer would mean increased opacity and reduction in glare. In alternate embodiments use of darker pigments in the decorative layer while providing patterns on the glass substrate could also result in enhanced blocking of light resulting in reduced glare perception for the same pattern area coverage. In all embodiments of the present disclosure, the decorative layer is provided using an enamel, lacquer or ink composition.

In accordance with the present disclosure the perimeter of the pattern, the pattern area coverage, and the area to perimeter ratio required for arriving at the predefined geometry of the pattern is dependent on various factors such as the glare mitigation percentage and visual light transmission required by the end user and geographical location. In another embodiment the glare mitigation percentage and visual light transmission can also be provided by the architect depending on end- user’s requirement, further depending on which the predefined geometrical patter can be arrived at. The visual light transmission of the patterned glass substrate in accordance with the present disclosure can be varied depending on the geographical location and the end user’s/customers requirement. In an alternate embodiment the desired visual light transmission can also be provided by an architect depending on the location, pattern and end user’s visual comfort.

Similarly, the percentage of glare reduction also depends on geographical location and end user’s requirement. While the desired glare reduction can be indicated by an architect, in alternate embodiment, the maximum glare reduction for a desired visual transmission can be arrived at for an optimized geometrical pattern. The percentage of glare reduction is in a varied range depending on the geometrical patterns. The patterns can be provided in such a way, to meet the end user’s aesthetic choice and requirement.

In some embodiments the pattern area coverage will vary depending on the crucial parameters such as area to perimeter ratio, pattern area coverage, percentage glare mitigation, and percentage visual light transmission. In alternate embodiments the pattern area coverage will vary depending on the combination of crucial parameters along with the end user’s requirements and geographical location.

The patterned glass substrate in accordance with the present disclosure having a predefined geometrical pattern, in terms of optimized area to perimeter ratio per unit pattern and the pattern area coverage ensures that the glare mitigation by cutting down light transmission is greater than glare aggravation due to light scattering along the edges of the predefined geometrical pattern. This will help in providing end-users/customers with patterned glass retrofitting solutions offering a combination of both aesthetic appeal and excellent visual comfort.

The present disclosure further provides a method for making a patterned glass substrate having maximized glare mitigation under direct and diffused light. The method comprises the steps of providing a transparent substrate which is clean and dried. The method further comprises applying a decorative layer in a predefined geometrical pattern, on a surface of the transparent substrate.

The glass substrate of the current disclosure onto which the predefined geometrical pattern is provided, is a coated substrate, clear substrate, soda lime or a borosilicate glass. One or more surfaces of the glass substrate is a clear, extra clear, acid etched or sand blasted (on full surface or specific designs). The glass substrate in accordance with the present disclosure is an annealed glass substrate, laminated glass substrate with PVB, EVA or PET, a heat strengthened glass substrate, or a toughened glass substrate.

The decorative layer in accordance with an embodiment of the present disclosure is in a predefined geometrical pattern. The predefined geometrical pattern has an optimized area to perimeter ratio per unit pattern across a predetermined pattern area coverage. In accordance with the present disclosure the decorative layer provided in the form of a pattern is selected from a group including but not limited to lines, circles, square, triangle, oval, rectangle, octagon, parallelogram, trapezoid, pentagon, hexagon, stars, gradients, abstract shapes or a combination thereof.

The method includes pre-treatment of the glass substrate and then providing the decorative layer in a predefined geometrical pattern on the surface of the glass substrate and curing the decorative layer. In some embodiments the method can also include providing a coating of a protective layer over the decorative layer and curing the protective layer. In alternate embodiments protective layer over the patterned layer may be optional.

The decorative layer in accordance with the present disclosure is provided by various coating techniques including but not limited to screen printing, embossed roller coating, digital printing, curtain coating, gravure coating, ink -jetting, spray painting or dip coating. In an embodiment the decorative layer on the patterned substrate can also be provided using lacquer paints or enamels. In some embodiments, the decorative layer on the glass substrate is also applied in the form of stickers.

In an embodiment the predefined geometrical pattern is applied as a single layer on the glass substrate. In an alternate embodiment the predefined geometrical pattern is applied in multiple layers or colors using any of the above mentioned coating techniques. The predefined geometrical pattern may also carry certain functionality such as having a metallic, phosphorence, fluorescence, or retro-reflection effect.

In specific embodiments that use enamels capable of withstanding heating temperatures of glass, the method further comprises cleaning and drying the transparent substrate provided with the decorative layer in a predefined geometrical pattern. In accordance with the disclosed method the patterned glass substrate provided with predefined geometrical patterns can be handled, transported and also capable of undergoing mechanical processing such as cutting, edge grinding, beveling, drilling, sizing, finishing, shaping etc. In an embodiment the patterned transparent substrate is then heat treated to a temperature ranging between 580 °C and 800 °C for a period ranging between 2 minutes and 20 minutes, preferably for a maximum period of 15 minutes, depending on the type of oven and the thickness of the glass substrate. In an embodiment the thickness of the glass substrate is in the range of 3 mm to 12 mm.

In accordance with this specific embodiment the patterned glass substrate with the decorative layer of the current disclosure can further be transported before being cut into specific sizes and then subjected to processes including washing, grinding, drilling, shaping, toughening etc. This results in the reduction of glass wastage as the glasses could be cut, stored and used at a later date.

The patterned glass prepared in accordance with the present disclosure with the decorative layer provided on the glass substrate in a manner, such that the optimized area to perimeter ratio of per unit pattern and the pattern area coverage ensures the glare mitigation by cutting down light transmission is greater than glare aggravation due to scattering of light along the pattern edges.

In another aspect, the present disclosure provides a method for optimizing a patterned glass substrate in order to obtain a maximized glare mitigation under direct and diffused light. The method for optimizing the patterned glass in accordance with the present disclosure comprises critical steps of tailoring certain crucial parameters which will in turn ensure that the glare mitigation is maximized, when a pattern having such tailored parameters is provided on the glass substrate.

The method includes the steps of, a) determining glare conditions of a non-patterned transparent glass substrate in terms of daylight glare probability (DGP), b) determining total area of the glass substrate intended to be provided with a decorative layer in the form of a geometrical pattern c) determining a desired percentage of glare mitigation and/or visual light transmission, d) determining area to perimeter ratio and pattern area coverage based on the percentage of glare mitigation and/or visual light transmission, e) determining a suitable geometrical pattern for obtaining the desired glare mitigation and visual light transmission, along with the determined area to perimeter ratio and pattern area coverage, and f) providing the suitable geometrical pattern on the determined area of the glass substrate,

The existing glare conditions of a non-patterned glass substrate in terms of daylight glare probability (DGP) is evaluated using standard measurements or simulations known in the art. An existing measurement methodology has been used in the present disclosure to evaluate the DGP of a non-patterned glass substrate. The images of the view through a glass facade fitted with the non-patterned glass substrate at the site/location of a building are captured by a DSLR camera fitted with a fish eye lens (180 deg field of view), at multiple exposures by varying the shutter speed and keeping the aperture constant. Simultaneously, the luminance in the scene is measured externally using a luminance meter focused on a neutral grey square on a color card. The captured images are merged into HDR images and the measured luminance value is input on the grey square in the image to calibrate the scene luminance captured in the image to match the actual conditions, i.e., the luminance measured at the location of the building. The prepared HDR image is then processed in Evalglare which runs on Radiance Engine and computes the glare metrics of which DGP is used here. DGP depends on the geographic location of the building, building orientation with respect to sun-path and glass properties.

The same measurement process has been performed to measure the glare of various samples, i.e., all the patterned glass substrates in accordance with the present invention and DGP has been calculated. Subsequent to determining the glare conditions, the overall area of the glass substrate where the decorative layer with symmetric patterns is desired to be provided is determined. In an alternate embodiment the area of the desired overall area of asymmetric patterns such as abstract shapes are also determined. For example, only a specific area of the glass substrate where the decorative layer is desired to be provided can be indicated by the architect or the end user. Further to which, desired percentage of glare mitigation and visual light transmission is determined. In some embodiments depending on end user’s requirement and geographical location, either the percentage of glare mitigation or the percentage of visual light transmission is determined.

In accordance with the present disclosure the percentage glare mitigation of the glass substrate is calculated by the change in the daylight glare probability of a patterned glass with respect to the daylight glare probability of a non-patterned glass. The % glare mitigation is calculated as = (PGP of the non-patterned sample - PGP of the patterned glass sample)

PGP of non-patterned sample

The method further includes determining area to perimeter ratio and decorative pattern area coverage based on percentage of glare mitigation and visual light transmission. In some embodiments the area to perimeter ratio and decorative pattern area coverage is either based on percentage of glare mitigation or percentage of visual light transmission. Further depending on the determined glare mitigation, visual light transmission, area to perimeter ratio and decorative pattern area coverage, a suitable pattern that satisfies all the determined parameters is then arrived at.

The decorative layers are provided in various ways in which the total area of the glass or the required shape can be filled with patterns. In an embodiment the decorative patterns are provided in various sizes and print coverages.

The method for optimizing the patterned glass further includes, determining which of the determined parameters satisfy the desired glare reduction and/or desired visual light transmission, and then provide a decorative layer. In an embodiment the desired glare reduction and/or desired visual light transmission can be provided by the architects. In an alternate embodiment the desired glare reduction and/or desired visual light transmission can be provided by the customer/end user as well. The decorative layer with a predefined geometry can then be provided depending on these factors, also taking into consideration the aesthetics.

Providing such predefined geometrical patterns which have been obtained by optimizing the crucial parameters ensures that the glare mitigation by cutting down light transmission is greater than glare aggravation due to scattering of light along the pattern edges.

The glare mitigation is presented by change in glare per unit change in pattern area coverage. The percentage light scattering of the glass substrate is calculated by change in a scattering peak intensity with respect to a baseline intensity. Calculating the light scattering at the edges of the pattern is important to show that the glare mitigation achieved in accordance with the present invention is greater than the light scattering at the edges of the pattern.

The light scattering is presented by the change in glare aggravation per unit change in area to perimeter ratio. Method for measurement of glare conditions in terms of DGP and method for measurement of light scattering at the edges of the pattern is further detailed below under separate headings, for the sake of sufficiency and clarity to the one ordinary skill in the art.

Measurement of glare conditions by DGP method

1. Calculation of DGP is done using an existing measurement methodology wherein images of the view through a glass facade fitted with a non-patterned glass substrate at the site/location of a building are captured by a DSLR camera fitted with a fish eye lens (180 deg field of view), at multiple exposures by varying the shutter speed and keeping the aperture constant. Simultaneously, the luminance in the scene is measured externally using a luminance meter focused on a neutral grey square on a color card. The captured images are merged into HDR images and the measured luminance value is input on the grey square in the image to calibrate the scene luminance captured in the image to match the actual conditions i.e., the luminance measured at the location of the building. The prepared HDR image is then processed in Evalglare which runs on Radiance Engine and computes glare metrics of which DGP or Daylight Glare Probability is used here.

2. This measurement method was done to measure the glare of the various samples and DGP was calculated.

3. The DGP values measured for the patterned glass samples were compared against the DGP of a non-patterned reference substrate to understand increase or decrease in glare.

The % glare mitigation is calculated as =

(DGP of the non-patterned sample - DGP of the patterned glass sample)

DGP of non-patterned sample

4. The HDR images are then converted to false color renders to see the luminance maps on Photosphere. This provides information on the intensity of light at various parts of the image. E.g. The edge scattering of light was observed here.

Measurement of light scattering at edges of pattern 1. A more quantitative method of observing the edge scattering is by processing images in ImageJ or Matlab from where the profile of increase or decrease in luminance intensity can be seen for a cross-sectional profile.

2. The high and low peak area can be calculated to quantify the edge scattering and bulk blocking of light respectively, with respect to the non-patterned glass substrate.

% change scattering is calculated as = [scattering peak intensity - baseline intensity| * 100 baseline intensity

Further referring to FIG. 6 graphical representation, showing the luminance intensity profile across a 2D cross section of a line print. The first part of the graph is at the sky portion of the image, outside the print. The luminance is at a constant range. Then, the bump in intensity of luminance observed is at the edge of the pattern which is scattering peak intensity. The next part is a big drop in the luminance intensity which is in the bulk region of the pattern. This continues through the width of the pattern. The second bump is the other edge of the pattern with a scattering peak. The luminance intensity moves the baseline intensity which is luminance intensity of the sky seen through the bare glass. In some embodiments smoothening out edges of patterns could also reduce the extent of edge scattering, thereby reducing the edge contribution to visual discomfort. In order to quantify the light scattering a measurement based methodology has been used, which is detailed below.

Methodology to quantify light scattering at edges of a pattern

Vertical eye illuminance (Ev) quantifies the amount of light that is perceived by the eye. Ev accounts for the total light reaching the eye and includes the edge scattering observed. The set up shown in Figure 7 was used for vertical eye illuminance measurements.

The set up consists of a slot for placing the glass samples at a 0.5 m distance from a standard light source. The camera (substituting the eye) is placed about 1.5 m away from the glass sample. An array of lux sensors were also placed in the same location. Measurements were made with the camera following the HDRI protocol. The lux sensors were used to validate the trends observed in measurements by the HDRI protocol. The inside of the rectangular tube is lined with black matte finish paint to minimize stray reflections. Daylight glare probability depends directly on the vertical eye illuminance received by the observer. Since the patterned glass samples scatter light at the edges, it is understood that the Visible Light Transmission which is a product specification of the patterned glass may not entirely capture the perceived light transmission from patterned glass samples considering the edge effects observed. For patterned glass, the visible light transmission is specified based on the print coverage of the pattern, its opacity, and the light transmission of the coated glass. Therefore, for a better understanding of the correlation between product specification and perception it is necessary to first understand the relationship between the vertical eye illuminance and the visible light transmission of a non-patterned glass sample. The calibration study was first conducted on a set of standard coated glass samples without patterns.

Non-pattemed samples (for determination of the calibration curve)

The samples (A, B, C & D) having the same coating with different VLTs shown in Table 1 were used for the study. Measurements of the vertical eye illuminance were performed in the controlled set-up by using the HDRI protocol and using an array of lux sensors. Glare measurements were also performed using the HDRI protocol and a plot showing the trend of DGP with respect to the %VLT. The results are shown in Figure 8. The product specification used here is %VLT. The vertical eye illuminance (Ev) and the area-averaged luminance of the view (increases linearly with %VLT). The slope of this linear plot is 20.5. This is a calibration curve which can be used to determine the perceived light transmission of patterned glass samples.

Patterned samples The vertical eye illuminance and the area average luminance were measured for patterned glass samples of increasing coverage densities as shown in Figure 9a. The DGP was also measured as shown in Figure 9b.

In the case of the patterned glass, it is observed that the relationship between the vertical eye illuminance and coverage density is non-linear. The same trend is observed in the plot between the area-averaged luminance and coverage density. Since DGP depends on both these quantities, the glare perception is also found to vary non-linearly with coverage density.

The measured Ev includes the total light perceived including the edge scattering. Based on the above determination the further key parameters can be evaluated. Details of the same are also produced below.

1. Determination of perceived light transmission = Using the slope of the calibration curve from the non-patterned samples i.e. 20.5, the perceived light transmission (%) of the patterned samples can be determined

2. Determination of the %contribution by the edges to light transmission = % perceived light transmission measured - expected % light transmission calculated based on print coverage

3. Determination of % glare reduction = (DGP of patterned glass substrate measured - DGP of non-patterned glass substrate) / DGP of bare substrate * 100

In accordance with the method disclosed for optimizing the patterned glass substrate the reduction in glare is directly proportional to a function of area to perimeter ratio per unit pattern and the pattern area coverage, as represented below: where, A and P represent the area and perimeter of a unit pattern and C represents the print coverage. Therefore, for any given requirement of light transmission and visual comfort, either by the end user or an architect, a set of patterns of specific dimensions can be recommended in accordance with the present disclosure.

The patterned glass substrate thus optimized in accordance with the present disclosure having a defined geometry in terms of perimeter, area and pattern coverage, wherein the glare reduction is directly proportional to a function of area to perimeter ratio of per unit pattern and the pattern coverage is obtained. The parameters tailored in accordance with the present disclosure provide a predefined geometrical pattern on the glass substrate which ensures that the glare reduction is achieved along with a combination of aesthetic appeal of patterned glass and visual comfort.

In order to arrive at the area to perimeter ratio and pattern area coverage, image analysis algorithm methodology is used.

Methodology to determine the area to perimeter ratio

1. The JPEG or PNG image of the sample is read into an image processing software like ImageJ or using the Image processing toolbox on MATLAB .

2. Color thresholding is performed on the loaded image. Color thresholding is an image processing method that creates a binary image based on setting a threshold value on the pixel intensity of the original image. While most commonly applied to grayscale images, it can also be applied to color images. The threshold of image intensity (relative image lightness) is set manually at a specific value or automatically set by an application. Pixels below that set threshold value are converted to black (bit value of zero), and pixels above the threshold value are converted to white (a bit value of one). The thresholding process is sometimes described as separating an image into foreground values (black) and background values (white).

3. Outlines of the shapes are extracted using appropriate commands.

4. Area and perimeter are calculated for each isolated shape using appropriate commands. Further using the values achieved, the A/P ratio of individual shapes or the A/P ratio of the whole pattern i.e. total area (pixels)/total perimeter (pixels) is determined. This method can be applied to images of any shape to arrive at the area to perimeter ratio including any abstract image.

Methodology to determine the pattern coverage area

1. The JPEG or PNG image of the sample is read into an image processing software like ImageJ or using the Image processing toolbox on MATLAB.

2. The image is converted into a binary image. i.e. pixels below that set threshold value are converted to black (bit value of zero), and pixels above the threshold value are converted to white (a bit value of one). The thresholding process is sometimes described as separating an image into foreground values (black) and background values (white).

3. % area covered by the black pixels is determined using appropriate commands. The same method can be applied for images of any shape.

By using the above methodologies, we can arrive at a pre-defmed geometry in terms of perimeter, area and pattern area coverage. Although, the patterned glass substrate as described herein in connection with exterior applications such as bus shelters, windows and facades, the application can be extended and implemented to a wide variety of automotive and architectural applications, or any combination thereof, as desired. The optimized patterns can be incorporated on windshields and / or side-lites in automobiles and this could cut down the glare discomfort typically experienced by the drivers. Highly reflective glass articles in building interiors could also be patterned in accordance with the present invention to reduce glare spots.

The present invention is further disclosed by the following examples, which are intended for purposes of illustration and not limitation.

EXAMPLES

The following examples are provided to explain and illustrate various embodiments of the patterned glass substrate of the present invention and do not in any way limit the scope of the invention as described and claimed: SAMPLE DESCRIPTION

300 mm x 300 mm samples were used for the analysis. The patterns with varying designs and coverages were printed on bare glass substrate via screen printing and studied. A non-patterned glass substrate was used as a comparative sample.

SAMPLES TESTED

• Glass patterned with lines of width 3.175 mm of print coverages: 20%, 30%, 40%, 50%, 57%, as illustrated in FIG. la

• Glass patterned with circles of diameter 3.175 mm of print coverages: 20%, 30%, 40%, as illustrated in FIG. lb

• Glass patterned with hole pattern, as illustrated in FIG. lc.

• Glass patterned with gradient hole pattern, as illustrated in FIG. Id.

• FIG. la and lb are compared against the non-patterned base substrate as reference comparative sample.

TESTING METHODOLOGY

• These samples were tested for glare against direct and diffuse sunlight.

• The testing protocol follows the High Dynamic Range (HDR) imaging technique wherein the images of the patterned glass are acquired at multiple exposures and then built together to form an HDR image.

• The HDR image is post processed in Photosphere for luminance calibration and the false color renders of the luminance maps are observed.

• The calibrated HDR image is then processed in Evalglare, a Radiance based tool to calculate the Daylight Glare Probability (DGP).

The percentage reduction in glare is normalized with respect to the DGP of the non-patterned bare substrate so as to demonstrate the % glare reduction as a virtue of just the patterns as follows:

(DGP of the non-patterned sample - DGP of the patterned glass sample)

DGP of non-patterned sample • Each of the circle and line patterned glass samples were studied to understand the relationship between the % glare reduction and the geometrical parameters of a pattern.

The bulk region of the printed patterns cuts down on light transmission equivalent to its opacity, resulting in reduced glare. The edges of the patterns scatter light, thereby aggravating glare (observed in Figure 1). A net decrease in glare is observed when the amount of light blocked by the bulk region of the pattern is higher than the amount of light scattered by the edges of the patterns. This can be predicted using the perimeter/area ratio of the unit pattern.

The perimeter/area ratio of circle patterns:

The perimeter/area ratio of line patterns: where,

Pc = Perimeter of the circle pattern Ac = Area of the circle pattern PL = Perimeter of the line pattern AL = Area of the line pattern n = No. of patterns per unit area d = Diameter of a unit circle a = Width of a unit line 1 = Length of a unit line

Example 1:

To compare the influence of A/P of patterns by virtue of its shape, 2 shapes circles and lines were compared. Circle patterns the ink is printed as circles on glass, so the ink is discontinuous as a pattern on circles. In order to compare them, the width of the unit line pattern, ‘a’ is kept equal to the diameter of the unit circle pattern, ‘d’, i.e. d = a. In this special case, the perimeter/area ratio of the circular patterns is twice that of the line patterns (from Eq. (1) and (2)). Figure 3 shows the comparison of % glare reduction calculated for line patterned glass and circle patterned glass for different print coverages: 30% and 40%. It was observed that the % glare reduction by a line patterned glass is observed to be higher than that of circle patterned glass, when the circle diameter is equal to the line width (seen in Figure 3).

Example 2

In this experiment, circle and line patterns of diameter/width of 4 mm and 12 mm were tested. Figure 4 shows the comparison of percentage reduction in glare calculated for line patterned glass and circle patterned glass at 35% print coverage, but of two different pattern dimensions. The same trend observed previously was observed (glare reduction by lines is higher than circles at the same coverage and pattern dimension). This dataset proves that increasing A/P ratio for the same unit pattern resulted in higher reduction in glare.

Figure 5 shows the % reduction in glare for line patterned glass as a function of increasing print coverages at a constant area/perimeter ratio. As the coverage of the pattern increases, higher reduction in glare is observed. However, at low print coverage, the scattering of light at the pattern edges is not compensated by the cutting down of light transmission by the bulk region of the unit pattern. This results in a higher glare compared to a bare non-patterned glass. In other words, only when the print coverage on glass is higher than a threshold print coverage, glare reduction is observed. The threshold print coverage value is expected to be a function of the area/perimeter ratio and varies depending on the dimensions of the unit pattern.

From the above examples it is clearly understood that glare reduction by a patterned glass is a function of the area to perimeter ratio of its unit pattern and the reduction in glare is also a function of the overall print coverage of the pattern on glass.

OBSERVATIONS i. From the luminance maps (refer to FIG. 2), it is observed that the bulk region of the patterns block light and reduce glare, while the edges of the patterns scatter light and contribute to glare. ii. It was observed that the glare reduction by a pattern is a function of its area/perimeter ratio. iii. Higher glare reduction was observed for increasing print coverage provided the coverage is higher than a threshold print coverage, which is specific to each pattern. iv. Vertical or horizontal orientation of lines do not have an impact on the glare.

Example 3

In this experiment, hole patterns were tested holes, the ink is printed as the continuous layer, and the holes are the regions where there is no ink. This sample consists of an inverted circle pattern in which the patterns are made of holes and the remaining portion of the glass is covered by the frit enamel. HDRI analysis of the samples was performed and the resulting false-color render of the luminance distribution in the image is shown in FIG. lc. The DGP was found to be 0.33. The print coverage of the sample was calculated via image analysis as detailed earlier. The vertical eye illuminance through this sample was measured to be 634 lux. Using this and the relationship between perceived light transmission and vertical eye illuminance, the perceived light transmission through this sample was calculated to be 31.7%. The DGP of the hole patterns measured was found to be 0.45. Using these quantities, the % of glare reduction and % of edge contribution to light scattering were further determined.

Figure 10 shows the study of the luminous intensity along the entire hole pattern edges. Profiling across a single hole -pattern was done. From the luminous intensity profile shown in Figure 10, two scattering peaks were observed at either side corresponding to the pattern edge.

Calculation of percentage of glare reduction for Example 3, hole pattern

DGP of non-patterned glass sample measured = 0.45

DGP measured for patterned glass sample disclosed in Example 3 = 0.33

% glare reduction = (0.45 - 0.33)/0.33 * 100 = 36.4%

Calculation of percentage contribution by the edges to light scattering hole pattern

% contribution = Perceived light transmission - Expected light transmission calculated based on print coverage

Perceived light transmission from measurements = 31.7% To determine expected light transmission calculated based on print coverage, the following formula is used:

= (% VLT of the non-patterned substrate/ 100) * (% non-patterned area/100) * 100 Print coverage of sample determined by image analysis = 54.6%

% VLT of the bare substrate (ST 136) = 34%

% non-patterned area = 100 - Print coverage determined by image analysis = 100 - 54.6 = 45.4%

Expected light transmission calculated based on print coverage = 34/100 * 45.4/100 * 100 = 15.4%

% contribution by the edges to light scattering and therefore light transmission = Perceived light transmission - Expected light transmission calculated based on print coverage

= 31.7% - 15.4%

= 16.3%

Example 4

In this experiment, gradient hole patterns were tested. This sample consists of an inverted pattern in which the patterns are made of gradient holes and the remaining portion of the glass is covered by the frit enamel. Additionally, the hole patterns reduce in size at a constant ratio. HDRI analysis of the samples was performed and the resulting false-color render of the luminance distribution in the image is shown in FIG. Id. The DGP was found to be 0.31. The print coverage of the sample was calculated via image analysis described in the previous section. The % area of black pixels was found to be 40.2% Therefore, the print coverage of this sample was found to be 59.8%. The vertical eye illuminance through this sample was measured to be 574 lux. Using this and the relationship between perceived light transmission and vertical eye illuminance, the perceived light transmission through this sample was calculated to be 28.7%. The DGP of the non-patterned substrate measured at the same conditions was found to be 0.45. Using these quantities, the %glare reduction and %edge contribution to light scattering were determined. Figure 11 shows the luminous intensity along the pattern edges. Profiling across a row of hole pattern was performed. From the luminous intensity profile shown in Figure 11 , peaks of an overall width corresponding to the width of the gradient hole -pattern was observed. The peaks corresponding to the smaller holes were found to be sharp whereas the peaks corresponding to the larger holes were found to be broader. The broader peaks have a set of scattering peaks at either end corresponding to the pattern edges. The trough in the middle is the non-patterned portion of the glass substrate.

Calculation of percentage of glare reduction for Example 4, gradient hole pattern

DGP of non-patterned glass sample measured = 0.45

DGP measured for this patterned glass sample disclosed in Example 4 = 0.31 % glare reduction = (0.45 - 0.31)/0.31 * 100 = 45.2%

Calculation of percentage contribution by the edges to light scattering gradient hole pattern

% contribution = Perceived light transmission - Expected light transmission calculated based on print coverage

Perceived light transmission from measurements = 28.7%

To determine expected light transmission calculated based on print coverage:

= (% VLT of the non-patterned substrate/ 100) * (% non-patterned area/100) * 100 Print coverage of sample determined by image analysis = 59.8%

% VLT of the non-patterned substrate (ST 136) = 34%

% non-patterned area = 100 - Print coverage determined by image analysis = 100 - 59.8 = 40.2%

Expected light transmission calculated based on print coverage = 34/100 * 40.2/100 * 100 = 13.67%

% contribution by the edges to light scattering and therefore light transmission

Perceived light transmission - Expected light transmission calculated based on print coverage = 28.7% - 13.67%

= 15.03%

Example 5

300 * 300 mm clear glass samples with white circle patterns and black circle patterns of identical dimensions were tested using the above recited methods. By matching the false-color image with the scale-bar, it is evident that the luminance on the white dots is higher than that on the black dots. This difference is translated into the glare measurements as well as shown in Figure 13a (white pattern) and 13b (black pattern). The glare through the black circle patterned sample, Figure 12 b was found to be less (DGP of 0.58) than that through the white circle patterned sample (DGP of 0.66), Figure 12 a.

The luminance profile across a unit pattern also shows the difference between the non-patterned region and the patterned region is higher in the case of the black pattern and lesser in the case of the white pattern. This implies that the color of the pattern also has an impact on the glare measured.