Lens appearance customization based on variable skin reflectance

Abstract

This disclosure relates to an optical element (10) adapted to be worn in front of the eyes (20) of a human wearer. The optical element comprises a dye composition configured such that when the optical element (10) is worn by a wearer having a given skin reflectance and is illuminated by a light source from a scene (30): - a first beam (1) is transmitted by the optical element (10) towards the wearer, the first beam having a first chromaticity, - a second beam (2) is transmitted by the optical element (10) towards the scene (30) after being reflected by the wearer's skin (40), the second beam having a second chromaticity, and - the absolute difference between the second chromaticity and the first chromaticity is greater than 6.

Description

Field of the Invention

[0001] The present invention generally relates to the field of ophthalmic optical devices. More specifically, the present invention relates to optical elements, methods for determining dye compositions, methods for manufacturing stained optical elements, uses of optical elements for attenuating light, and uses of optical elements for enhancing color vision. Background Art

[0002] One concern in the field of optical devices is to provide sunglasses or light-colored lenses where the transmitted color seen by the wearer is different from the color seen by an external observer.

[0003] This would allow for a fashionable, specific look, or conversely, to hide colors or filters.

[0004] It has been proposed to include a semi-reflective element (or mirror) on the object-side surface of a colored optical lens. By doing so, the color of the reflected light is not affected by the tint of the optical lens. Alternatively, the optical lens can include a stack of a first colored material layer, a semi-reflective mirror, and a second colored material layer. By doing so, the reflected light has a different color from the transmitted light.

[0005] One drawback of the prior art is that although adding a mirror to an optical lens allows for differentiating between the internal and external colors, such lenses do not appear to the observer as colored lenses.

[0006] Rather, such lenses mainly appear as a colored surface because the color is specularly reflected rather than diffusely reflected at the lens surface.

[0007] Moreover, such a mirror prevents the observer from seeing the wearer's eyes and the skin around the eyes.

[0008] In this context, there is a need for an optical article that exhibits a transmitted color seen by the wearer that is different from the color seen by an external observer, while not preventing the observer from seeing the wearer's eyes and the skin around the eyes. Summary of the Invention

[0009] The present invention is defined by the appended independent claims. Additional features and advantages of the concepts disclosed herein are set forth in the following description.

[0010] This disclosure aims to improve this situation.

[0011] To this end, this disclosure describes an optical element adapted to be worn in front of the eyes of a human wearer, the optical element comprising a dye composition that includes at least one absorptive dye, the dye composition being configured such that when the optical element is worn by a wearer having a given skin reflectance and is illuminated by a light source from a scene:

[0012] - The first light beam is transmitted by the optical element towards the wearer, and the first light beam has a first chromaticity in the CIE L*a*b* color space.

[0013] - The second light beam is transmitted by the optical element towards the scene after being reflected by the wearer's skin, and the second light beam has a second chromaticity in the CIE L*a*b* color space, and

[0014] - The absolute difference between the second chromaticity and the first chromaticity is greater than 6.

[0015] Due to the use of the reflectance spectrum of the skin and the fact that the light passes through the lens twice, the optical element allows the wearer to see a transmitted color that is different from the color seen by an external observer.

[0016] In one example, at least one of the first chromaticity and the second chromaticity is less than 10, preferably less than 3. In another example, the first chromaticity is less than 10, preferably less than 3, in the CIE L*a*b* color space, and the second chromaticity is greater than the first chromaticity, preferably greater than 20, in the CIE L*a*b* color space. This allows the wearer to perceive less color change in the seen scene, while the optical element appears colored to an observer.

[0017] In this regard, another aspect of the present invention relates to the use of an optical element for attenuating light incident on the eyes of a human wearer having a given skin reflectance, so as to change the wearer's color perception as little as possible, wherein the optical element comprises at least one absorptive dye configured such that when the optical element is worn by the wearer and irradiated by a light source from the scene:

[0018] - The first light beam is transmitted by the optical element towards the wearer, and the first light beam has a first chromaticity in the CIE L*a*b* color space.

[0019] - The second light beam is transmitted by the optical element towards the scene after being reflected by the wearer's skin, and the second light beam has a second chromaticity in the CIE L*a*b* color space.

[0020] - The first chromaticity is less than 10, and

[0021] - The absolute difference between the second chromaticity and the first chromaticity is greater than 6.

[0022] According to an embodiment of the present invention, in the range from 475 nm to 650 nm:

[0023] - When the optical element has a light transmittance greater than 0.8*TvD65 when exposed to light conditions corresponding to the standard light source D65, in the CIE L*a*b* color space, the absolute difference between the second chromaticity and the first chromaticity is greater than 16.

[0024] - When the optical element has a light transmittance between 0.43 and 0.8*TvD65 when exposed to light conditions corresponding to the standard light source D65, in the CIE L*a*b* color space, the absolute difference between the second chromaticity and the first chromaticity is greater than 15, and

[0025] - When the optical element has a light transmittance between 0.18 and 0.43*TvD65 when exposed to light conditions corresponding to the standard light source D65, in the CIE L*a*b* color space, the absolute difference between the second chromaticity and the first chromaticity is greater than 10.

[0026] In one example, the second chromaticity is less than 10, preferably less than 3, in the CIE L*a*b* color space, and the first chromaticity is greater than the second chromaticity, preferably greater than 20, in the CIE L*a*b* color space. This allows the optical element to appear colored to the wearer but neutral or gray to an observer.

[0027] In this regard, another aspect of the present invention relates to the use of an optical element for enhancing the color vision of a human wearer having a given skin reflectance, wherein the optical element comprises at least one absorptive dye configured such that when the optical element is worn by the wearer and illuminated by a light source from a scene:

[0028] - A first light beam is transmitted by the optical element towards the wearer, the first light beam having a first chromaticity in the CIE L*a*b* color space, and

[0029] - A second light beam is transmitted by the optical element towards the scene, the second light beam having a second chromaticity in the CIE L*a*b* color space,

[0030] - In the CIE L*a*b* color space, the second chromaticity is less than 10, and

[0031] - The absolute difference between the second chromaticity and the first chromaticity is greater than 6.

[0032] In one example, in the range from 475 nm to 650 nm, when exposed to light conditions corresponding to the standard light source D65, the absorbance of the optical element is less than 0.2*TvD65, and the relative visual attenuation coefficient for identifying / detecting incandescent signal lamps is not less than 0.8 for Qred, not less than 0.6 for Qyellow, not less than 0.6 for Qgreen, and not less than 0.6 for Qblue.

[0033] In another example, in the range from 475 nm to 650 nm:

[0034] - When the optical element has a light transmittance greater than 0.43*TvD65 when exposed to light conditions corresponding to the standard light source D65, in the CIE L*a*b* color space, the absolute difference between the second chromaticity and the first chromaticity is greater than 7.

[0035] - When the optical element has a light transmittance between 0.18 and 0.43*TvD65 when exposed to light conditions corresponding to the standard light source D65, in the CIE L*a*b* color space, the absolute difference between the second chromaticity and the first chromaticity is greater than 6.

[0036] Therefore, the optical element meets the driving standard defined in the latest version of ISO12312 as of the filing date.

[0037] According to an embodiment of the present invention, the first light beam has a first hue in the CIE L*a*b* color space, and the second light beam has a second hue in the CIE L*a*b* color space. In the CIE L*a*b* color space, the absolute difference between the second hue and the first hue is less than 67, preferably less than 50.

[0038] According to an embodiment of the present invention, the optical element as described in any one of the preceding claims, wherein the first light beam has a first hue in the CIE L*a*b* color space, and the second light beam has a second hue in the CIE L*a*b* color space. In the CIE L*a*b* color space, the absolute difference between the second hue and the first hue is greater than 20, and both the first chromaticity and the second chromaticity are greater than 10.

[0039] In one example, the dye composition includes a combination of absorptive dyes. The optical properties of each absorptive dye and their relative proportions in the dye composition allow for fine-tuning of the absorption spectrum of the dye composition.

[0040] According to an embodiment of the present invention, the above optical element contains at least one activatable absorptive dye. Various types of activatable dyes are well known to those of ordinary skill in the art. As a result, the optical element can be switched between different configurations, i.e., it can be switched between an active state and an inactive state in the case of an external source such as an external light source (such as a photochromic or electrochromic type dye).

[0041] In addition, in at least one configuration, at least one of the first chromaticity and the second chromaticity is less than 10, and the absolute difference between the second chromaticity and the first chromaticity is greater than 6.

[0042] In this regard, another aspect of the present invention relates to an optical device that at least includes:

[0043] - The above optical element, wherein at least one of the absorptive dyes is activatable, and

[0044] - A processing circuit, the processing circuit including a processing unit, a non-transitory storage medium, and a communication module,

[0045] The processing circuit is configured to receive an input command and trigger, in response, the activation or deactivation of at least one of the absorptive dyes, such that the optical device switches or switches from one configuration to a configuration in which, preferably, at least one of a first chromaticity and a first chromaticity is less than 10, and the absolute difference between a second chromaticity and the first chromaticity is greater than 6.

[0046] Another aspect of the present invention relates to a method for determining a dye composition, the method comprising:

[0047] - Obtaining a skin reflectance, a first target chromaticity, and a second target chromaticity,

[0048] - Preferably, at least one of the first target chromaticity and the second chromaticity is less than 10 in the CIE L*a*b* color space,

[0049] - The absolute difference between the second target chromaticity and the first target chromaticity is greater than 6 in the CIE L*a*b* color space; and

[0050] - Applying a non-linear least squares analysis to a plurality of absorptive dyes in a dye database to determine a dye composition, the dye composition including at least one absorptive dye from the dye database, such that when the dye composition is incorporated in an optical element worn by a wearer having the skin reflectance and the optical element is illuminated by a light source from a scene:

[0051] - A first light beam is transmitted by the optical element towards the wearer, the first light beam having a first chromaticity equal to the first target chromaticity in the CIE L*a*b* color space, and

[0052] - A second light beam is transmitted by the optical element towards the scene after being reflected by the wearer's skin, the second light beam having a second chromaticity equal to the second target chromaticity in the CIE L*a*b* color space.

[0053] Thus, the method allows for the determination of a dye composition for any skin reflectance, and thus for any skin color, which dye composition, when incorporated in an optical element worn by a wearer having the skin color, looks different to the wearer and to an observer. The inventors have found that non-linear least squares analysis is the most suitable type of optimization algorithm in terms of the computation time required for convergence in order to determine the dye composition.

[0054] Another aspect of the present invention relates to a method for manufacturing a dyed optical element, the method comprising dyeing the optical element with the above-determined dye composition. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] To more fully understand the description provided herein and its advantages, reference is now made to the following brief description taken in conjunction with the accompanying drawings and specific embodiments, in which like reference numerals represent like parts.

[0056] Figure 1 An exemplary optical element is depicted being worn by a wearer and further being illuminated by a light source from a scene.

[0057] Figure 2a An exemplary total skin reflectance spectrum of a so-called NIST skin is depicted, and Figure 2b the total skin reflectance of a so-called Pantone SkinTone(TM) 2R05SP (close to NIST skin) is depicted.

[0058] Figure 3 , for an exemplary optical element, spectra corresponding to an inward appearance and an outward appearance respectively are depicted when the optical element is worn by a wearer, the wearer's skin having an exemplary skin reflectance spectrum of the Pantone SkinTone TM 2R05SP type.

[0059] Figure 4 An exemplary optical device is depicted.

[0060] Figures 5 to 12 , for eight exemplary optical elements respectively, spectra corresponding to an inward appearance and an outward appearance respectively are depicted when the optical element is worn by a wearer, the wearer's skin having an exemplary skin reflectance spectrum of the Pantone SkinTone TM 2R05SP type. DETAILED DESCRIPTION

[0061] In the following description, the drawings are not necessarily to scale. In particular, the relative dimensions of the cavities with respect to the rigid elements may be exaggerated. For purposes of clarity and conciseness or for purposes of providing information, certain features may be shown in a generalized or schematic form. Additionally, although multiple different embodiments of manufacturing and using are discussed in detail below, it should be understood that many inventive concepts can be implemented in a variety of environments as described herein. The embodiments discussed herein are merely representative and do not limit the scope of the present invention. It will also be apparent to those skilled in the art that all technical features defined with respect to a method can be transposed to a system individually or in combination, and vice versa, all technical features with respect to a system can be transposed to a method individually or in combination.

[0062] Now refer to Figure 1 , which depicts an exemplary optical element (10), more specifically an ophthalmic lens of a pair of glasses.

[0063] The ophthalmic lens has two opposite principal surfaces: hereinafter the eye side and the object side.

[0064] The eye side principal surface faces the wearer's eye when worn, while the object side principal surface faces the object or scene, and when worn, the object side principal surface will face the object or scene that the wearer sees through the ophthalmic lens.

[0065] Further assume that the optical element (10) is colored. The hue is obtained by a dye composition comprising at least one absorptive dye or a combination of different absorptive dyes. Generally, the hue of the optical element is defined to reduce the visible light transmittance Tv of a D65 light source to conform to a specific category of sunglasses:

[0066] - An optical element with a visible light transmittance Tv of 80% or higher, also known as a "Category 0" optical element

[0067] - An optical element with a visible light transmittance Tv between 46% and 79%, also known as a "Category 1" optical element

[0068] - An optical element with a visible light transmittance Tv between 18% and 45%, also known as a "Category 2" optical element.

[0069] In Figure 1 , the glasses are depicted as being worn by a wearer and illuminated by one or more light sources from a scene (30).

[0070] The optical path (L) is further depicted and corresponds to a light beam originating from one of such light sources and illuminating the object side principal surface of the optical element (10).

[0071] A first light beam (1) is transmitted by the optical element (10) towards the wearer and at least illuminates the wearer's eye (20).

[0072] The optical path corresponding to the first light beam (1) is further depicted in Figure 1 as originating from the object side principal surface of the optical element (1) and illuminating a patch of skin (40) around the wearer's eye (20).

[0073] The color of the first light beam (1) perceived by the wearer is affected by the hue of the optical element. In other words, the color of the first light beam depends on the nature of the dye composition.

[0074] The first light beam (1) is diffusely reflected by the wearer's skin (40) at a second location towards the eyeball-side main surface of the optical element (10), and then at a third location, it transmits through the optical element (10) and returns to the scene (30) as the second light beam (2).

[0075] The optical path corresponding to the second light beam (2) is further depicted in Figure 1 as transmitting from the wearer's skin (40) and eyeball, through the optical element (10), and originating from the object-side main surface of the optical element (1) and pointing towards the scene (30).

[0076] Since the second light beam (1) corresponds to a light beam originating from the scene (30), and this beam transmits through the optical element (10) twice and is combined with the diffuse reflection by the wearer's skin (40), the color of the second light beam (2) is affected not only by the hue of the optical element but also by the reflectivity of the wearer's skin (40). Moreover, the second light beam is affected by the internal reflections present at each interface of the successive materials having different refractive indices defined in the optical element.

[0077] As a general consideration, the following terms are used throughout this document:

[0078] - The first light beam has a first chromaticity, denoted as C*, and a first hue, denoted as H*, in the CIE L*a*b* color space, corresponding to an "inward appearance", denoted as T%, that is, related to the light transmitted by the optical element towards the wearer.

[0079] - The second light beam has a second chromaticity, denoted as C**, and a second hue, denoted as H**, in the CIE L*a*b* color space, corresponding to an "outward" appearance, denoted as R%, that is, related to the light transmitted by the optical element through the wearer, then diffusely reflected by the wearer's skin / eyeball, and then transmitted again by the optical element towards the scene (e.g., towards an observer facing the wearer), and

[0080] - The difference between the second chromaticity and the first chromaticity is denoted as Cboost = C** - C*, and the difference between the second hue and the first hue is denoted as Hboost = H** - H*.

[0081] Two embodiments are then developed:

[0082] - In the first embodiment, the inward appearance is light, "neutral" or light gray, and corresponds to a lower first chromaticity C* perceived by the wearer, while the outward appearance is more saturated and fashionable, and thus corresponds to a higher second chromaticity C** perceived by the wearer. As a result, compared with the inward light beam, the outward light beam exhibits a "positive color enhancement", or

[0083] - In contrast, in the second embodiment, the inner appearance exhibits a relatively high first chromaticity C*, thus enhancing the wearer's perception of a specific color, while the outer appearance corresponds to a much lower second chromaticity C**, such that the color perception of an observer viewing the wearer's eyes is hardly affected by the presence of the optical lens (10), while the wearer's color perception is maximized. As a result, compared to the inward beam, the outward beam exhibits a "negative enhancement", i.e., the color becomes darker.

[0084] In both embodiments, the difference between the inner appearance (T%) and the outer appearance (R%) is maximized, and Cboost is a non-zero integer, positive in the first embodiment above and negative in the second embodiment.

[0085] There are several different factors that can affect the optimization of the inner and outer appearances.

[0086] One of these factors is any modification of the natural reflectance curve of the wearer's skin, for example through the use of makeup.

[0087] Another factor is the use of interference coatings, but this method, which requires complex and expensive manufacturing steps, will be ignored.

[0088] This last factor is outside the scope of the present invention and will not be further developed, as the present invention is entirely based on the optimization of the dye composition and excludes the use of interference coatings for the purpose of optimizing the difference between the inner and outer appearances of the beam.

[0089] Yet another factor that can be affected in order to maximize the difference between the inner appearance (T%) and the outer appearance (R%) is the design of the optical element (10). More specifically, the transmittance curve of the optical element can be adjusted by selecting a specific dye composition. Incidentally, it should be noted that the transmittance curve of the optical element is always strictly the same in both directions, as dictated by the laws of physics.

[0090] Throughout this document, different specific exemplary optical elements are described, and the C*, C**, and absolute Cboost values corresponding to these exemplary optical elements are provided.

[0091] C* is inherent in the transmittance curve of the optical element (10).

[0092] C** and Cboost are affected by the skin reflectance of the wearer, which is external to the optical element (10), and by internal reflections and interferences at the different interfaces between the different materials that make up the optical element and the surrounding (air) of the optical element. The reflectance of the wearer's skin varies from person to person.

[0093] In fact, according to the present invention, the transmittance curve of the optical element (10) is customized by selecting a specific dye composition for the skin of a specific individual or for a specific type of skin shared by a group of individuals.

[0094] For example, the specific values of C** and Cboost disclosed in this document always explain the "reference skin reflectance" corresponding to a "reference wearer" (i.e., a mental construct rather than an actual wearer). The skin reflectance of the "reference wearer" corresponds to the average skin reflectance spectrum (50) obtained from the study of "Reflectance Measurements of Human Skin" conducted by NIST (i.e., skin reflectance as a function of wavelength), the photographic illustration of which is accessible on the https: / / www.nist.gov / programs-projects / reflectance-measurements-human-skin date of filing and is reproduced in Figure 2.

[0095] To maximize the difference between the inward appearance (T%) and the outward appearance (R%), the dye composition is specifically configured, taking into account at least one given skin reflectance corresponding to an actual wearer or a reference wearer, such that at least one of the first chromaticity and the second chromaticity is preferably less than 10, and the absolute difference between the second chromaticity and the first chromaticity is greater than 6. This can only be achieved by configuring the dye composition to filter the exact correct wavelengths according to the skin reflectance under consideration.

[0096] Making one of the first chromaticity and the second chromaticity less than 10 allows one of the inward appearance or the outward appearance to be a neutral color in terms of color.

[0097] Making both the first chromaticity and the second chromaticity greater than 10, and the first hue and the second hue greater than 20 allows the inward appearance and the outward appearance to be colored and to be perceived as being different in color from each other.

[0098] Making the absolute difference |Cboost| between the first chromaticity and the second chromaticity greater than 6 allows the inward appearance and the outward appearance to be clearly two different colors for the human eye, one of which may be neutral or light gray.

[0099] Also making the absolute difference |Hboost| between the first hue and the second hue greater than 6, and each of the first chromaticity and the second chromaticity higher than 20 allows the inward appearance and the outward appearance to be each perceived as having a specific color (hue) for the human eye.

[0100] In some exemplary embodiments, the dye composition is configured such that |Cboost| is greater than a threshold value, which is greater than 6, such as 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, etc.

[0101] An exemplary method for determining a dye composition that meets the above requirements is described below.

[0102] Transmittance spectra of a variety of absorptive dyes are obtained, for example, calculated or acquired from a dye database. The absorptive dyes may include existing real dyes available on the market. The absorptive dyes may further include so-called "perfect" dyes that absorb light only within a limited wavelength range, such as a 20-nm wavelength range. For example, a "perfect dye" has a uniform absorbance within the limited wavelength range and can be specifically created by specialized companies (Exciton, Epolin..) with a specific chemical composition according to the targeted limited wavelength range. The absorptive dyes may include activatable dyes, i.e., dyes that change color upon activation. Examples include temperature-sensitive dyes activated by temperature changes, electroactive dyes activated when a potential difference is applied, piezoelectric dyes activated when pressure is applied, photochromic dyes activated when a light difference is applied, etc.

[0103] By combining the retrieved transmittance spectra of such absorptive dyes, the transmittance spectra of various dye compositions can be determined. More specifically, a dye composition is defined as including any combination of a variety of the absorptive dyes in any corresponding proportions. As a result, the first chromaticity C* and the first hue H* of the light transmitted through an optical element colored with a given dye composition can be calculated.

[0104] In addition, as Figure 2a or Figure 2b depicted in, the skin reflectance spectrum is considered for a given person or group of people. The skin reflectance spectrum corresponds to a specific skin color, for example, associated with a specific wearer or a reference wearer.

[0105] Taking into account the given transmittance spectrum of a given dye composition, the given skin reflectance spectrum, and the given materials of the different layers (substrate base material, hard coating, anti-reflection coating, anti-static coating...) that make up the optical element, the second chromaticity C** and the second hue ** of the light transmitted through the optical element colored with the given dye composition, then reflected by the skin with the given skin reflectance spectrum, and then transmitted through the optical element again can be obtained.

[0106] In an illustrative embodiment, the outgoing beam spectrum can be modeled by:

[0107] (T% of the optical element * R% of the skin * T% of the optical element) + R% of the interference at different interfaces

[0108] Various optimization methods allow for the determination of a dye composition that meets specific predefined requirements regarding a first chromaticity C* and a second chromaticity C**. According to the requirements defined above, a first target chromaticity and a second target chromaticity are obtained or defined such that preferably at least one of the first target chromaticity and the second target chromaticity is less than 10 in the CIE L*a*b* color space, and the absolute difference between the second target chromaticity and the first target chromaticity is greater than 6 in the CIE L*a*b* color space. Additional requirements and constraints can be further defined. Examples of additional requirements can be preset values of a first target hue or a second target hue. Examples of additional constraints can be that the dye composition should have a transmittance exceeding a given threshold within a given wavelength range.

[0109] Generally, the optimization method includes testing various dye compositions. Testing a dye composition includes determining at least the values of a first chromaticity C* and a second chromaticity C** for this composition, as well as the values of any additional relevant parameters regarding predefined requirements or constraints, such as H* and H**.

[0110] Examples of such optimization methods can include least squares analysis or non - linear least squares analysis.

[0111] In another embodiment of the present invention, a subtractive mixing method known to those skilled in the art can be used to calculate the concentration of each primary colorant. Then, the lens can be manufactured after selecting its color from the color range established in the foregoing manner.

[0112] Several tested dye compositions may differ from each other in the nature of the dyes they include. In this regard, one objective can be to select suitable dyes to be incorporated into the dye composition.

[0113] In addition, several tested dye compositions can have the same composition and differ only in the relative proportions of the dyes they include. For example, multiple absorptive dyes can be preselected as components of the dye composition to be determined, and one stage of the optimization method can be to determine the most appropriate relative proportions of the preselected dyes, i.e., the proportions that allow the closest match between the calculated first chromaticity C* and first hue H* and the corresponding first target chromaticity and first target hue, as well as between the calculated second chromaticity C** and second hue H** and the corresponding second target chromaticity and second target hue.

[0114] For example, the optimization method can be a multi-stage method. The purpose of the first stage can be to determine a first absorptive dye among a plurality of candidate dyes that best matches the constraints and requirements. The purpose of the second stage can be to identify a second absorptive dye among the candidate dyes other than the first dye such that a combination of a specific relative proportion of the first absorptive dye and the second absorptive dye exhibits a closest match to the constraints and requirements. Other stages can allow for further refining the dye composition by adding more than one component at a time.

[0115] Once the dye composition is determined, an optical element (10) comprising the dye composition can be manufactured. For example, the dye of the dye composition can be inserted into the substrate of an ophthalmic lens, such as a Trivex substrate, or into an additional layer covering the substrate, such as an epoxy resin layer.

[0116] Reference Figure 3 , for an exemplary optical element (10), which shows a first spectrum (51) corresponding to the inward appearance (T%). The first spectrum is the spectrum of a first light beam (1) when the optical element is irradiated with a white light source corresponding to the standard light source D65 from a scene and the first light beam (1) is transmitted through the optical element (10) towards the wearer.

[0117] Figure 3 Also shown is a second spectrum (52) corresponding to the outward appearance (R%). In the above case, the second spectrum is the spectrum of a second light beam (2) transmitted back to the scene when the first light beam (1) is diffusely reflected towards the optical element (10) according to a reference skin reflectance spectrum.

[0118] Figure 3 Also shown for reference is the considered reference skin reflectance spectrum (50).

[0119] Table 1 below indicates a series of values corresponding respectively to Figure 3 the first spectrum (51) and the second spectrum (52) depicted in, more specifically, the values of L*, a*, b*, a first chroma C*, a second chroma C**, a first hue H* and a second hue H** in the CIE L*a*b* color space are indicated together with the corresponding RGB values at a 10° angle of incidence. Table 1 also indicates the light transmittance and light reflectance of the optical element (10) when irradiated with a white light source corresponding to the standard light source D65 at a 2° angle of incidence, denoted as Tv(%) and Rv(%), respectively, as shown in Table 1 below.

[0120] Light transmittance measurements were performed on a sample in the form of a disc with a diameter of 25 mm and a thickness of 1.5 mm, made of a Trivex substrate with an HMC coating (Crizal Sun on the concave and convex surfaces) deposited on each of its first and second surfaces, using a Cary 50 spectrometer sold by Varian. A Pantone 2R05SP artificial skin sample was placed against the surface (second surface) of the optical element opposite the light source (0 mm distance).

[0121] L a b Chromaticity Hue R G B (％) (51) 75 6 -2 6 345 194 181 186 Tv = 47 (52) 39 20 7 21 21 210 135 136 Rv = 11

[0122] In this example, as Figure 3 the spectrum shows, the dye composition is optimized to emphasize the red tones of the reference wearer's skin:

[0123] - The second spectrum (52) shows that the light blue wavelengths are significantly absorbed by the optical element (10): the outward appearance (R%) is saturated red, where the high chroma value C** exceeds 21

[0124] - While the light red and light blue wavelengths of the first spectrum (51) are transmitted, and the inward appearance (T%) is faint and almost colorless, where the low chroma value C* of purple / light gray is 6. Thus, the first spectrum (51) shows that most of both the light blue and light red wavelengths are transmitted by the optical element (10) towards the wearer: the inward appearance (T%) is neutral gray, where the low chroma value C* is less than 6.

[0125] As a result, Cboost exceeds 15.

[0126] This can only be achieved by a dye composition that is configured to filter the precise correct wavelengths according to the skin color under consideration.

[0127] More generally, using combinations of known dyes, the dye composition contained in the optical element (10) can be optimized so that the optical element (10) appears more colored to an observer than to the wearer when worn. More specifically, in this regard, the dye composition can be optimized such that:

[0128] - The inward appearance (T%) resulting from the transmittance spectrum of the dye composition corresponds to a first chroma C* that is less than 10, for example less than 6, while

[0129] - The outward appearance (R%) resulting from the combination of the transmittance spectrum of the dye composition and the reflectance spectrum of the reference wearer's skin, along with any internal reflections at the interfaces between the different material layers of the optical element and air, corresponds to a second chroma C** that is greater than the first chroma C*, where Cboost = C** - C* ≥ 6. A second chroma C** greater than 15 is particularly sought.

[0130] For example, the dye composition can be optimized such that, for an optical element having a visible light transmittance Tv of 80% or higher (also referred to as a "Class 0" optical element), Cboost is preferably greater than 10.

[0131] For example, the dye composition can be optimized such that, for an optical element having a visible light transmittance Tv between 46% and 79% (also referred to as a "Class 1" optical element), Cboost is preferably greater than 15.

[0132] For example, the dye composition can be optimized such that, for an optical element having a visible light transmittance Tv between 18% and 45% (also referred to as a "Class 2" optical element), Cboost is preferably greater than 16.

[0133] The possible color of the outward appearance (R*) is largely related to the skin color of the wearer. The reference skin reflectance spectrum (50) corresponds to Caucasian skin with an orange - red hue.

[0134] As a result, by calculating the ideal - theoretical - transmittance curve that allows the maximum Cboost of the reference wearer, the second spectrum (52) obtained with a dye composition having such a transmittance curve corresponds to an orange - red hue.

[0135] By calculating other possible theoretical transmittance curves that allow positive Cboost for the reference wearer, the second spectrum (52) obtained with dye compositions having these other possible transmittance curves corresponds to a mixture of at least one red wavelength and at least one other (non - red) wavelength. Thus, the possible color of the outward appearance (R*) for the reference wearer is centered around red (H** = 30°) on the CIE L*a*b color wheel and may extend from yellow (H** = 90°) to purple (H** = 340°).

[0136] In the case of the theoretical dye combinations, for the above - mentioned HMC lenses, the highest calculated values of Cboost for different given values of the second hue H** (taking into account the reference skin reflectance spectrum) are shown in Table 2 below.

[0137] H** Class 2, Tv = 40% Class 1, Tv = 60% Class 0, Tv = 90% Yellow (90°) 12 16 12 Orange (50°) 24 21 19 Red (30°) 24 21 15 Purple (340°) 7 5 0

[0138] Table 2

[0139] The other calculations have been performed under the following additional constraints: only combinations of commercial dyes are allowed, rather than the perfect dyes mentioned above, and they comply with the road use requirements for ophthalmic lenses. For example, according to the latest version of ISO 12312 at the filing date, these requirements stipulate that in the range of 475 nm to 650 nm, when exposed to the light conditions corresponding to the standard light source D65, the absorbance of the ophthalmic lens should be less than 0.2 * TvD65 (or conversely, the light transmittance should be greater than 0.8 * TvD65), and the relative visual attenuation coefficients for identifying / detecting incandescent signal lights should be not less than 0.8 for Qred, not less than 0.6 for Qyellow, not less than 0.6 for Qgreen, and not less than 0.6 for Qblue.

[0140] As a result of these calculations, Table 3 below shows the highest calculated values of Cboost for different given hues, considering the reference skin reflectance spectrum and also allowing compliance with the road use requirements.

[0141] Hue h* Class 2, Tv = 40% Class 1, Tv = 60% Class 0, Tv = 90% Yellow (90°) 10 10 12 Orange (50°) 13 18 17 Red (30°) 18 18 16 Purple (340°) 7 5 -

[0142] Table 3

[0143] Table 4 below indicates a series of values associated with twelve exemplary optical elements (10) that appear more color-revealing to an observer rather than the wearer when the reference wearer wears these exemplary optical elements.

[0144] <![CDATA[C* 10° > <![CDATA[h* 10° > R G B <![CDATA[Tv D65 %]]> <![CDATA[C** 10° > <![CDATA[h** 10° > Cboost #1 1 59 172 170 167 39 26 38 24 #2 8 335 192 176 186 45 23 24 14 #3 6 345 194 181 186 47 24 20 18 #4 5 51 181 171 166 41 23 37 18 #5 4 341 207 200 202 59 21 30 18 #6 2 91 169 167 161 39 16 58 13 #7 4 102 205 204 195 60 22 52 18 #8 4 54 178 170 165 40 27 52 24 #9 9 132 164 173 157 40 19 93 10 #10 10 110 202 202 181 60 20 92 10 #11 5 287 163 164 171 36 12 353 7

[0145] Table 4

[0146] More specifically, each exemplary optical element (10) is referred to using a corresponding identifier ID. The range of the identifiers is #1 to #12.

[0147] For each optical element so identified:

[0148] - Regarding the inward appearance (T%), the values indicating the first chroma (C*) and the first hue (H*) in the CIE L*a*b* color space, as well as the RGB values,

[0149] - Regarding the outward appearance (R%), indicating the second chroma (C**) and the second hue (H**) in the CIE L*a*b* color space, considering the skin reflectance corresponding to the reference skin reflectance spectrum, and

[0150] - Also indicating the light transmittance of the optical element (10) when irradiated by a white light source corresponding to the standard light source D65, denoted as Tv (%).

[0151] The inward appearance (T%) of all exemplary optical elements (10) corresponds to a first chromaticity C* that is less than or equal to 10 and thus appears neutral and gray to the wearer.

[0152] In addition, the outward appearance (R%) of all exemplary optical elements (10) corresponds to a second chromaticity C**, such that Cboost = C** - C* is greater than 6. The second hue H** is significantly different among the exemplary optical elements (10). In fact, considering the reference skin reflectance spectrum, #1 to #5 appear red to the observer, while #6 to #8 appear orange, #9 and 10 appear yellow, and #11 and 12 appear purple.

[0153] In yet another embodiment, a combination of known dyes can be used to optimize the dye composition to be included in the optical element (10) such that the optical element (10) appears more chromatic to the wearer rather than the observer when worn. For example, when worn, the optical element (10) may appear gray to the observer but be colored, such as blue, to the wearer.

[0154] To enhance this effect, the optical element (10) can be combined with a specific makeup having similar spectral management. For example, one can wear glasses with green lenses, which prevent the observer from seeing a slightly greenish makeup that is only fully revealed when the glasses are removed.

[0155] More specifically, in this regard, the dye composition can be optimized such that:

[0156] - The inward appearance (T%) resulting from the transmittance spectrum of the dye composition corresponds to the first chromaticity C*, while

[0157] - The outward appearance (R%) resulting from the combination of the transmittance spectrum of the dye composition and the reflectance spectrum of the reference wearer's skin corresponds to a second chromaticity C** that is less than the first chromaticity C* and also less than 10,

[0158] Cboost = C** - C* ≤ -6.

[0159] As already mentioned, the second chromaticity C** and the second hue H** depend not only on the transmittance spectrum of the dye composition but also on the reflectance spectrum of the wearer's skin.

[0160] As a result, for the optical element (10) to appear light gray to the observer when worn but be colored to the wearer, the maximum possible absolute value of Cboost, denoted as |Cboost|, is obtained when the first hue (H*) is the complementary color of the wearer's skin color.

[0161] The complementary color of the orange - red hue (30° hue) corresponding to the reference skin reflectance curve is blue - green (210° hue). Thus, in this case, the highest possible value of |Cboost| is obtained when the first hue H* is approximately 210° (blue - green). The range of possible values of the first hue H* that allows Cboost = C** - C* ≤ - 6 and C** < 10 is from 150° (green) to 270° (blue).

[0162] The values of Cboost have been calculated using combinations of theoretical dyes, using different given values of the first hue H* as constraints and considering the reference skin reflectance spectrum. The values are shown in Table 5 below.

[0163] H* Class 2, Tv = 40% Class 1, Tv = 60% Class 0, Tv = 90% Yellow (90°) >0 >0 >0 Green (150°) -14 -8 >0 Blue - green (210°) -21 -15 -6 Blue (270°) -18 -11 >0

[0164] Table 5

[0165] The values of Cboost have been further calculated using combinations of existing dyes obtained from a library, using different given values of the first hue H* as constraints, meeting the road - use requirements, and considering the reference skin reflectance spectrum. The values are shown in Table 6 below.

[0166] H* Class 2, Tv = 40% Class 1, Tv = 60% Class 0, Tv = 90% Green (150°) -11 -9 >0 Blue - green (210°) -9 -10 -5 Blue (270°) -9 -6 >0

[0167] Table 6

[0168] As described above, it can be seen that:

[0169] - The yellow first hue H* does not meet the requirement of making Cboost less than - 6,

[0170] - The blue - green first hue H* produces the best results and meets the said requirements even for class 0 optical elements (10), and

[0171] - The green or blue first hue H* also meets the said requirements, provided that the absorbance of the dye composition is high enough.

[0172] Table 7 below indicates a series of values associated with six exemplary optical elements (10) which, when worn by a reference wearer, appear colored to the wearer or observer and neutral to other subjects under consideration.

[0173] <![CDATA[C* 10° > <![CDATA[h* 10° > R G B <![CDATA[Tv D65 %]]> <![CDATA[C** 10° > <![CDATA[h** 10° > Cboost #13 22 270 151 176 212 40 6 285 -16 #14 19 270 186 207 240 59 8 300 -11 #15 6 41 195 181 176 49 18 61 +12 #16 13 231 197 230 242 74 2 165 -11 #17 22 210 117 184 191 40 8 169 -14 #18 22 210 147 213 220 58 7 187 -15

[0174] Table 7

[0175] More specifically, each exemplary optical element (10) is referred to using a corresponding identifier ID. The range of the identifier is from #13 to #18. For the wearer, identifiers #13 and #14 correspond to blue - looking optical elements, and identifier #15 corresponds to orange - looking (Figure 5 ),identifier #16( Figure 6 )、#17 and #18 correspond to cyan optical elements. For an observer looking through the optical element at the wearer's skin, they appear neutral (C** between 2 and <10). They all have negative Cboost values (between -16 and -7)

[0176] In contrast, identifier #15( Figure 5 ) appears orange (C** is 18) to an observer looking through the optical element at the wearer's skin, while the wearer perceives it as neutral, with C* below 10, i.e., 6. It defines a positive Cboost value.

[0177] Instead of the above example where one of the in-beam or out-beam colors is hardly perceptible (neutral or light gray with chroma below 10), in the following examples shown in Table 8, at least a perceptible color is defined in each of the in-beam and out-beam, and the in-beam or out-beam defines a more saturated color (absolute value of Cboost > 6, preferably higher than 10, more preferably higher than 20).

[0178] More precisely, in these examples, each of C* and C** is higher than 10, but in terms of color, C* and C** are defined to be below a predetermined value to define the at least perceptible color:

[0179] - For yellow, one of C* or C** is below 30, preferably below 40 (ID17, Figure 7 ),

[0180] - For red, both C* and C** are below 45, preferably below 50, (ID19, Figure 9 ),

[0181] - For blue, both C* and C** are below 30, preferably below 35, (ID21, Figure 11 )

[0182] - For green, both C* and C** are below 20, (not shown in ID23 and ID24)

[0183] In contrast, in some other examples in the same Table 8, both the in-beam and out-beam have a clearly perceptible color, the chroma of which is defined to be higher than a predetermined value according to the selected color, for example:

[0184] - For yellow, both C* and C** are greater than 30, preferably greater than 40 (ID18, Figure 8 ),

[0185] - For red, both C* and C** are greater than 45, preferably greater than 50, (ID20,Figure 10 )

[0186] - For blue, both C* and C** are greater than 30, preferably greater than 35, (ID22, Figure 12 )

[0187]

[0188]

[0189] Table 8

[0190] For each optical element thus identified:

[0191] - Regarding the inward appearance (T%), the values of the first chromaticity (C*) and the first hue (H*) in the CIE L*a*b* color space, as well as the RGB values,

[0192] - Regarding the outward appearance (R%), the second chromaticity (C**) and the second hue (H**) in the CIE L*a*b* color space, considering the skin reflectance corresponding to the reference skin reflectance spectrum, and

[0193] - Also indicate the light transmittance of the optical element (10) when irradiated by a white light source corresponding to the standard light source D65, denoted as Tv (%).

[0194] Now refer to Figure 4 , which depicts an exemplary optical device.

[0195] The optical device (60) includes at least one optical element (10) and a processing circuit (70). For example, the optical device can be a pair of glasses, and as a pair of optical elements, they are mounted on a spectacle frame that encloses the processing circuit.

[0196] The optical element (10) includes a dye composition that includes at least one activatable absorbing dye.

[0197] The optical element (10) further includes an activation module (11) that is configured to activate or deactivate at least one activatable absorbing dye upon receiving a corresponding output command. As a result, the optical element (10) can switch between different configurations. Each configuration is associated with a corresponding transmittance spectrum and thus with a specific combination of the inward appearance (T%) and the outward appearance (R%).

[0198] In at least one configuration, the dye composition is further configured such that, when the optical element (10) is worn by a wearer having a given skin reflectance and is irradiated by a light source from the scene (30):

[0199] - The first light beam (1) is transmitted towards the wearer by the optical element (10), and the first light beam has a first chromaticity in the CIE L*a*b* color space.

[0200] - The second light beam (2) is transmitted towards the scene (30) by the optical element (10) after being reflected by the skin (40) of the wearer, and the second light beam has a second chromaticity in the CIE L*a*b* color space.

[0201] - At least one of the first chromaticity and the second chromaticity is less than 10, and

[0202] - The absolute difference between the second chromaticity and the first chromaticity is greater than 6.

[0203] The processing circuit (70) includes at least a processing unit (71), a non-transitory storage medium (72), and a communication interface (73).

[0204] The communication interface (73) can interact with the human-machine interface (12) to receive an input command, thereby indicating a request to switch at least one optical element (10) from the current configuration to a desired configuration. The human-machine interface can be part of the optical device (60) and can be formed as a button or a slider. Alternatively, the human-machine interface can be part of a remote device, such as a user terminal, which is configured to transmit the input command to the communication interface (73) of the optical device (70) through a communication channel.

[0205] Such an input command can be processed by the processing circuit according to the instructions of a computer program stored on the non-transitory storage medium, so as to generate an output command. The output command is an electrical signal applied to the activation module (11) of at least one optical element (10). As a result, the activation module triggers the activation or deactivation of at least one absorptive dye, and the optical element (10) is switched from the current configuration to the desired configuration.

Claims

1. An optical element designed to be worn in front of the eyes of a human wearer, the optical element comprising a dye composition including at least one absorptive dye, the dye composition being configured to have a specific transmittance determined according to a given skin reflectance corresponding to an actual wearer or a reference wearer, such that when the optical element is worn by a wearer having the given skin reflectance and is irradiated by a light source from a scene: - A first light beam is transmitted by the optical element towards the wearer, the first light beam having a first chromaticity in the CIE L*a*b* color space, - A second light beam is transmitted by the optical element towards the scene after being reflected by the skin of the wearer, the second light beam having a second chromaticity in the CIE L*a*b* color space, and - The absolute difference between the second chromaticity and the first chromaticity is greater than 6.

2. The optical element according to claim 1, wherein, At least one of the first chromaticity and the second chromaticity is less than 10 in the CIE L*a*b* color space.

3. The optical element according to claim 1, wherein, The first chromaticity is less than 10 in the CIE L*a*b* color space, and the second chromaticity is greater than the first chromaticity in the CIE L*a*b* color space.

4. The optical element according to claim 3, wherein, In the range of 475 nm to 650 nm: - When the optical element has a light transmittance greater than 0.8*TvD65 when exposed to light conditions corresponding to the standard light source D65, in the CIE L*a*b* color space, the absolute difference between the second chromaticity and the first chromaticity is greater than 16, - When the optical element has a light transmittance between 0.43 and 0.8*TvD65 when exposed to light conditions corresponding to the standard light source D65, in the CIE L*a*b* color space, the absolute difference between the second chromaticity and the first chromaticity is greater than 15, and - When the optical element has a light transmittance between 0.18 and 0.43*TvD65 when exposed to light conditions corresponding to the standard light source D65, in the CIE L*a*b* color space, the absolute difference between the second chromaticity and the first chromaticity is greater than 10.

5. The optical element according to claim 1, wherein, The second chromaticity is less than 10 in the CIE L*a*b* color space, and the first chromaticity is greater than the second chromaticity.

6. The optical element according to claim 5, wherein, In the range of 475 nm to 650 nm: - When the optical element has a light transmittance greater than 0.43*TvD65 when exposed to light conditions corresponding to the standard light source D65, in the CIE L*a*b* color space, the absolute difference between the second chromaticity and the first chromaticity is greater than 7, - When the optical element has a light transmittance between 0.18 and 0.43*TvD65 when exposed to light conditions corresponding to the standard light source D65, in the CIE L*a*b* color space, the absolute difference between the second chromaticity and the first chromaticity is greater than 6.

7. The optical element according to claim 1, wherein, The first light beam has a first hue in the CIE L*a*b* color space, and the second light beam has a second hue in the CIE L*a*b* color space. In the CIE L*a*b* color space, the absolute difference between the second hue and the first hue is less than 67.

8. The optical element according to claim 1, wherein The first light beam has a first hue in the CIE L*a*b* color space, and the second light beam has a second hue in the CIE L*a*b* color space. In the CIE L*a*b* color space, the absolute difference between the second hue and the first hue is less than 20, and both the first chromaticity and the second chromaticity are greater than 10.

9. The optical element according to claim 1, wherein, In the range of 475 nm to 650 nm, when exposed to the light conditions corresponding to the standard light source D65, the absorbance of the optical element is less than 0.2 * TvD65, and wherein the relative visual attenuation coefficient for identifying or detecting incandescent signal lights is not less than 0.8 for Qred, not less than 0.6 for Qyellow, not less than 0.6 for Qgreen, and not less than 0.6 for Qblue.

10. The optical element according to claim 1, wherein, At least one absorptive dye can switch between an active state and an inactive state under an external source of an external light source.

11. A method for determining a dye composition, the method comprising: - obtaining a skin reflectance corresponding to an actual wearer or a reference wearer, - determining a desired transmittance based at least on the obtained skin reflectance such that when the dye composition having the desired transmittance is incorporated in an optical element worn by a wearer having the skin reflectance and the optical element is irradiated by a light source from a scene, ○ a first light beam is transmitted by the optical element towards the wearer, the first light beam having a first chromaticity in the CIE L*a*b* color space, ○ a second light beam is transmitted by the optical element towards the scene after being reflected by the skin of the wearer, the second light beam having a second chromaticity in the CIE L*a*b* color space, ○ the absolute difference between the second chromaticity and the first chromaticity is greater than 6 in the CIE L*a*b* color space; and - determining the dye composition having the desired transmittance based on the determined desired transmittance.

12. The method according to claim 11, wherein, Determining the desired transmittance includes: - obtaining a target spectral characteristic T%total of the second light beam, the target spectral characteristic satisfying a predetermined requirement regarding the second chromaticity, and - calculating the desired transmittance T% from T%total = T% * R%skin * T% + R%, where R%skin corresponds to the obtained skin reflectance and R% corresponds to a predetermined reflectance related to parasitic reflectance.

13. A method for manufacturing a dyed optical element, the method comprising dyeing an optical element with a dye composition determined according to claim 11 or 12.

14. Use of an optical element for attenuating light incident on the eyes of a human wearer having a given skin reflectance without changing the color perception of the wearer, wherein, The optical element comprises at least one absorptive dye configured to have a specific transmittance determined according to the given skin reflectance such that, when the optical element is worn by the wearer and illuminated by a light source from the scene: - A first light beam is transmitted by the optical element towards the wearer, the first light beam having a first chromaticity in the CIE L*a*b* color space, - A second light beam is transmitted by the optical element towards the scene after being reflected by the wearer's skin, the second light beam having a second chromaticity in the CIE L*a*b* color space, and - The absolute difference between the second chromaticity and the first chromaticity is greater than 6.

15. Use of an optical element for enhancing the color vision of a human wearer having a given skin reflectance, wherein, The optical element comprises at least one absorptive dye configured to have a specific transmittance determined according to the given skin reflectance such that, when the optical element is worn by the wearer and illuminated by a light source from the scene: - A first light beam is transmitted by the optical element towards the wearer, the first light beam having a first chromaticity in the CIE L*a*b* color space, and - A second light beam is transmitted by the optical element towards the scene, the second light beam having a second chromaticity in the CIE L*a*b* color space, and - The absolute difference between the second chromaticity and the first chromaticity is greater than 6.

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