The present invention generally relates to the field of light sensitivity.

It more particularly relates to a method for determining a visual discomfort and/or a visual performance of a user as well as a method for determining at least one filter for a transparent support able to improve or to maintain the visual comfort and/or visual performance of a user.

It also relates to a computer system and a computer program product comprising code instructions for performing said methods.

It has been observed that most people, close to 9/10 people, experience sensitivity to light. It can be a sensation of discomfort, headache, pain, dazzling, or fatigue. It is a visual discomfort which can occur in many lighting conditions, notably in lighting conditions specific for a given user.

It is known to correlate a light sensitivity to a light intensity. In this regard, it is possible to determine for a user a light sensitivity threshold at which a light exposure becomes uncomfortable.

However, it is difficult to evaluate such light sensitivity in a global manner. Indeed, a user may be exposed to different kinds of lights in his everyday life and may have a light sensitivity which varies with these kinds of lights. These light exposures are for example a warm light, a cold light or a blinking light.

As an example, a user may be very sensitive to cold light or blinking light but less sensitive to warm light. Another user may have a low sensitivity to warm and cold light but a high sensitivity to blinking light. It could thus be very difficult, notably for an eye care professional (ECP) or for the user himself, to accurately evaluate the light sensitivity of this user in a global manner. Particularly, it is difficult to easily obtain a meaningful quantity or value representative of the global light sensitivity of the user. Furthermore, directly combining these different light sensitivity thresholds do not allow to obtain a usable data actually representative of the light sensitivity of the user. Indeed, these data do not refer to the same luminance, to the same light conditions and/or the same nature of threshold. Combining these data is purely theoretical and do not provide usable data.

A problem that the invention aims to solve is thus to provide a parameter representative of a visual discomfort of a user with regard to different light conditions, this parameter allowing to compare light sensitivity of different users with each other.

To solve this problem, the invention provides a method for determining a visual discomfort and/or a visual performance of a user, the method comprising the following steps:

- providing at least two quantities representative of a light sensitivity threshold of the user;

- determining a resistance level based on said at least two quantities representative of a light sensitivity threshold of the user using a percentile scale based on a population baseline.

The eye resistance level is the capacity of the eye to manage the light intensity through photoreceptor and/or cortical processing, i.e. before the photoreceptors are saturated. Therefore, the eye resistance level is a global parameter which is able to evaluate the ability of a user to withstand light exposure.

Determining said eye resistance level depending of quantities representative of a light sensitivity threshold allows to enhance the accuracy and robustness of this parameter.

Using a percentile scale based on a population baseline allows to make it possible to use a same reference to gather these quantities representative of a light sensitivity threshold. When these quantities are expressed using a same reference, it is meaningful to combine thereof to determine said eye resistance level. As such, it is possible to obtain a parameter which depends on quantities representative of a light sensitivity threshold which may be obtained using different light conditions. For example, these light conditions can be a warm light exposure, a cold light exposure or a blinking light exposure. The present method allows to combine different information related to the light sensitivity of the user, for example for different light conditions, by using a same comparable reference scale.

According to an embodiment of the determining method, the step of determining said resistance level comprises:

- determining, for each quantity of said at least two quantities representative of a light sensitivity threshold of the user, a percentage value corresponding to the quantity representative of a light sensitivity threshold of the user in said percentile scale,

- determining said resistance level depending on said percentage values.

According to an embodiment of the determining method, said resistance level is determined as a combination of said percentage values.

According to an embodiment of the determining method, said percentage values are determined using a same percentile scale.

According to an embodiment of the determining method, said at least two quantities representative of a light sensitivity threshold of the user are determined by exposing the user to different light conditions.

According to an embodiment of the determining method, said at least two quantities representative of a light sensitivity threshold of the user comprise a first and a second quantities respectively representative of a low and a high light sensitivity threshold of the user, said high sensitivity threshold corresponding to a discomfort of the user greater than the low sensitivity threshold.

According to an embodiment of the determining method, said at least two quantities representative of a light sensitivity threshold of the user is at least one among: a warm light sensitivity threshold, a cold light sensitivity threshold and a blinking light sensitivity threshold.

According to an embodiment of the determining method, the step of determining said resistance level comprises:

- providing a plurality of resistance level groups based on a resistance level distribution of said population baseline, - determining a resistance level group corresponding to the user depending on said resistance level.

According to an embodiment of the determining method, it further comprises the step of determining at least one filter for a transparent support able to improve or to maintain the visual comfort and/or visual performance of a user based on said determined resistance level.

According to an embodiment of the determining method, a first resistance level is determined based on at least two quantities representative of a light sensitivity threshold of a first user using a percentile scale based on a first population baseline, said method further comprising;

- determining an updated population baseline based on said at least two quantities representative of a light sensitivity threshold of a first user and/or said first resistance level,

- determining a second resistance level based on at least two quantities representative of a light sensitivity threshold of a second user using a percentile scale based on said updated population baseline.

The invention also relates to a method for determining at least one filter for a transparent support able to improve or to maintain the visual comfort and/or visual performance of a user, the method comprising the following steps:

- determining a resistance level using the method according to any one of the preceding claims,

- determining, for each light environment among a group of light environments, an index representative of the level of protection required by the user;

- determining a score for each light environment among the group of light environments and for each filter among a group of filters, said score being representative of the capacity of the filter to reach the level of protection required by the user;

- determining at least one filter among the group of filters based on the scores of said at least one filter in a plurality of light environments among the group of light environments. According to an embodiment of the determining method, it further comprises a step of comparing said at least one quantity representative of a light sensitivity threshold of the user to a sensitivity reference to determine if the user is slightly sensitive or non-sensitive.

According to an embodiment of the determining method, said index representative of the level of protection required by the user is determined using a different questionnaire if the user is determined as a slightly sensitive or non sensitive user.

According to an embodiment of the determining method, the light sensitivity threshold is determined using a device configured to expose the user to an increasing light level and to determine the at least one quantity representative of the user's light sensitivity threshold based on a user's feedback representative of a discomfort.

According to an embodiment of the determining method, the method is a computer-implemented method.

The invention further provides a computer system for determining a visual discomfort and/or a visual performance of a user, the system comprising :

- a processor; and

- a memory with computer code instructions stored thereon, the memory operatively coupled to the processor such that, when executed by the processor, the computer code instructions cause the computer system to perform a method for determining a visual discomfort and/or a visual performance of a user, the method comprising the following steps:

• providing at least two quantities representative of a light sensitivity threshold of the user;

• determining a resistance level based on said at least two quantities representative of a light sensitivity threshold of the user using a percentile scale based on a population baseline.

The invention further provides a computer program product comprising code instructions for performing a method for determining at least one filter for a transparent support able to improve or to maintain the visual comfort and/or visual performance of a user, the method comprising the following steps: • providing at least two quantities representative of a light sensitivity threshold of the user;

• determining a resistance level based on said at least two quantities representative of a light sensitivity threshold of the user using a percentile scale based on a population baseline.

The invention is described in more detail below by way of the figures that show only one preferred embodiment of the invention.

Figure 1 schematically shows a graph of a plurality of sets of initial data expressed in a percentile scale based on a population baseline.

Figure 2 schematically shows a flowchart of a filter determining method.

Figure 3 schematically shows a light sensitivity test performed using a dedicated device.

Figures 4 to 6 schematically shows a data restitution regarding the results of the light sensitivity test displayed on displaying device for respectively warm light, cold light and blinking light conditions.

Figure 7, schematically shows a first questionnaire for sensitive or highly sensitive users.

Figure 8 schematically shows a second questionnaire for non-sensitive or slightly sensitive users.

Figure 9 shows a flowchart of a score determining step.

Figure 10 schematically shows a data restitution regarding the results of the questionnaire displayed on a displaying device.

Figure 11 shows schematically a data restitution of a filter determining step displayed on displaying device.

In the description which follows, the drawing figures are not necessarily to scale and certain features may be shown in generalized or schematic form in the interest of clarity and conciseness or for informational purposes. In addition, although making and using various embodiments are discussed in detail below, it should be appreciated that as described herein are provided many inventive concepts that may embodied in a wide variety of contexts. Embodiments discussed herein are merely representative and do not limit the scope of the invention. It will also be obvious to one skilled in the art that all the technical features that are defined relative to a process can be transposed, individually or in combination, to a device and conversely, all the technical features relative to a device can be transposed, individually or in combination, to a process.

The terms "comprise" (and any grammatical variation thereof, such as "comprises" and "comprising"), "have" (and any grammatical variation thereof, such as "has" and "having"), "contain" (and any grammatical variation thereof, such as "contains" and "containing"), and "include" (and any grammatical variation thereof such as "includes" and "including") are open-ended linking verbs. They are used to specify the presence of stated features, integers, steps or components or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps or components or groups thereof. As a result, a method, or a step in a method, that "comprises", "has", "contains", or "includes" one or more steps or elements possesses those one or more steps or elements but is not limited to possessing only those one or more steps or elements.

The present invention provides a method for determining a visual discomfort and/or a visual performance of a user. To this end, a specific physiologic parameter is determined: the eye resistance level.

The resistance level is the capacity of the eye to manage the light intensity through photoreceptor and/or cortical processing. If the light exposure is lower to the eye resistance level, the visual processing is optimal on the retina, i.e. the comfort and vision are optimal due to a quick adaptation. If the light exposure is higher to the eye resistance level, the photoreceptors are saturated ( Mainster MA, Turner PL. Glare's causes, consequences, and clinical challenges after a century of ophthalmic study. American journal of ophthalmology. 2012;153(4):587-593 and Efalov VJ. Rod and cone visual pigments and phototransduction through pharmacological, genetic, and physiological approaches. J Biol Chem. 2012;287(3): 1635-1641 ), neural hyperexcitability appears ( Mainster MA, Turner PL. Glare's causes, consequences, and clinical challenges after a century of ophthalmic study. American journal of ophthalmology. 2012;153(4):587-593 ), inducing discomfort, disability and pain for the user ( Noseda R, Kainz V, Jakubowski M, et al. A neural mechanism for exacerbation of headache by light. Nat Neurosci. 2010; 13(2) : 239-245. doi: 10.1038/ nn.2475 ) .

Eye resistance level thus refers to a limit before an over light exposure inducing a saturation of the photoreceptors causing discomfort, pain.

This method comprises the provision of a plurality of quantities representative of a light sensitivity threshold of the user. These quantities are preferably an illuminance expressed in lux.

By "sensitivity to light" of the user, what is meant is any relatively intense and prolonged reaction or modification of comfort or visual performance in relation to a temporary or continuous light flux or stimuli.

The light sensitivity threshold may be determined based on measurements using a dedicated device. This dedicated device may be a device configured to emit light toward one or both eyes of the user. The light sensitivity threshold may be determined depending on a response provided by the user subsequently to the light exposure. This response may be intentional by asking the user to indicate when a discomfort very disturbing occurs or determined by an external device configured to detect physical response to the user to a given light flux. In both cases, the quantity representative of a light sensitivity threshold of the user may be determined as a radiometric parameter or a photometric parameter.

A photometric parameter may be the illuminance (Lux) which is to a luminous flux incident on a surface (e.g. the front of the eyes) or the luminance (cd/m ² ) which is a luminous flux per unit solid angle per unit projected source area. A photometric parameter may also be the luminous exposure (Lux second) which is the time-integrated illuminance.

A radiometric parameter is the energy of the eye without taking into account eye sensitivity to wavelength (visibility). Said radiometric parameter may be the irradiance or flux density (Watt per square meter, i.e. W/m ² ) which is the radiant flux received by a surface per unit area. This is sometimes also confusingly called "intensity". Said radiometric parameter is equivalent to Illuminance in radiometry. Said radiometric parameter may also be the spectral irradiance or spectral flux density (Watt per square meter, per meter, i.e. W/m ³ ) which is the irradiance on a limited range of wavelength, e.g. only blue light. Said radiometric parameter may be the radiance (Watt per steradian per square meter, i.e. W.srTnv ² ) which is the radiant flux emitted, reflected, transmitted or received by a surface, per unit solid angle per unit projected area. Radiance is equivalent to Luminance in radiometry. Said radiometric parameter may also be the spectral radiance (Watt per steradian per square meter, per meter, i.e. W.srTnr ³ ) which is the radiance of a surface per unit of wavelength. Alternatively, said radiometric parameter may be a number of photon reaching the eye per second on all visible spectrum or a limited part of the spectrum or the troland (cd/m ² .mm ² ) which is the luminance weighted by pupil size.

The light sensitivity threshold may be set to define different levels or natures of discomfort of the user. In other words, the level or nature of the light sensitivity threshold may vary among the plurality of quantities representative of a light sensitivity threshold of the user. Hence, said plurality of quantities representative of a light sensitivity threshold of the user mays comprise a first quantity representative of a first light sensitivity threshold of the user and a second quantity representative of a second light sensitivity threshold of the user.

A variation of the nature or level of the light sensitivity threshold preferably refers to different symptoms of the user. As an example, the light sensitivity threshold may identify a just perceptible discomfort or a very disturbing discomfort. A just perceptible discomfort may refer to a start of tension in the eyelids of the user or tingling in the eyes. A very disturbing discomfort may refer to a moment when a significant effort is required to keep the eyes open.

In a preferred embodiment, said plurality of quantities representative of a light sensitivity threshold refer to different levels of discomfort of the user. In other words, said at least two quantities representative of a light sensitivity threshold of the user may comprise a first and a second quantities respectively representative of a low and a high light sensitivity threshold of the user, said high sensitivity threshold corresponding to a discomfort of the user greater than the low sensitivity threshold. The low light sensitivity threshold may refer to a just perceptible discomfort and the high light sensitivity threshold may refer to a very disturbing discomfort. More generally, the different light sensitivity thresholds may comprise a low, at least one intermediate and a high light sensitivity thresholds.

Determining the resistance level based on different levels of discomfort of the user allows to obtain a more detailed view of the light discomfort of the user. Indeed, the user may experience an early starting discomfort but a very late disturbing discomfort. On the contrary, another user may experience very close just perceptible and very disturbing discomforts. Considering different levels of light sensitivity threshold allows to better reflect the sensitivity of the user.

Furthermore, quantities representative of a light sensitivity threshold may be determined by exposing the user to different light conditions or environments.

It has been observed that a light environment cannot be accurately defined by only considering a single parameter as light intensity, this light environment is dynamic and composed of a plurality of components allowing to better describe thereof. Light may be defined as comprising at least four main components (called "4D"): an intensity component, a spatial component, a temporal component and a spectral component.

The intensity component refers to the luminous flux emitted by a light source in Lumen. The intensity component induces an illuminance at the wearer's position expressed in Lux. The illuminance may be determined using a light sensor disposed at a user's eye position which measures the illuminance in Lux induced by a light source. Some of the factors affecting the illuminance are the energetic intensity of a light source (the initial volume), the distance between the user and the source (the volume at any point along a light path) and any modifying elements in the light path (air, clouds, filters, reflectors, etc.). For example, the amount of outdoor light a person is exposed to can vary depending on geographical location, season, time of day, local weather, etc. The intensity component may refer to any one of the radiometric and photometric parameters previously mentioned.

The spatial component is the relative position of the light source regarding the user. This relative position depends on the angular distance between the user and the light source. The spatial component can be punctual or wide, and it can affect the individual's perception of light. Thus, for a given radiant flux, a punctual light source will have a higher luminance due to its smaller size. For example, vehicle headlights of similar radiant flux differ in luminance according to their size and distance.

The temporal component defines the period during which the light source emits. Indeed, light may be present for a short or long period of time, which may change the perception of the light by the user. Exposure to light for a given duration may be continuous or intermittent (which may also vary in frequency). In other words, the user may be exposed to a blinking light. For instance, car headlamps may only contribute to the light environment for a few seconds and move constantly across the field of vision.

The spectral component refers to the spectrum of the light which is emitted and its associated energy. This spectrum may be expressed using the wavelength of the light flux in nanometers. As an example, the visible spectrum of the light is comprised between 380 nm and 780 nm. A light flux of white light may appear warmer or colder depending on its spectrum. The spectral component may also be directly expressed as a color of light, e.g. a cold or warm white light. Emitting light reflecting a cold or warm light, e.g. by emitting more blue light or more red light, allows to respectively simulate substantially artificial or natural light or different light ambiance. Varying the color of light emitted toward the user allows to vary the light spectrum. Light sensitivity of the user can thus be determined with regard to a variation of the spectral component of the light.

At least two of these components may be combined to obtain specific light conditions representative of a predetermined environment, e.g. an environment representative of a frequent daily situation that can be a source of discomfort for the user.

Said resistance level is then determined based on said at least two quantities representative of a light sensitivity threshold of the user. The resistance level is determined using a percentile scale based on a population baseline. A "percentile scale" is a scale wherein the distribution of ordered values is partitioned into 100 intervals containing the same number of data (100-order quantiles).

The "population baseline" is a plurality of initial data representative of light sensitivity threshold of a set of initial users. By "initial users" we mean users which participate to a similar determination of quantities representative to light sensitivity threshold before the present method is performed on said user. In other words, initial users provide objective and/or subjective data allowing to build-up a reference scale expressed as a percentile scale.

A set of initial data is preferably provided for each quantity representative of a light sensitivity of the user. In doing so, when a first quantity representative of a light sensitivity threshold of the user is determined using first light conditions, a first set of initial data obtained using said first light conditions is provided. This first set of initial data comprises a plurality of quantities representative of a light threshold of the initial users. Using the same light conditions for each of the set of initial data and the quantity representative of a light sensitivity threshold of the user allows to compare thereof using the same conditions of experiment.

In a preferred embodiment, the population baseline comprises at least two sets of initial data respectively corresponding to said at least two quantities of a light sensitivity threshold of the user.

An example of a graph 30 of a plurality of sets of initial data expressed in a percentile scale based on a population baseline is shown on figure 1.

Said population baseline comprises six sets of initial data: a first set of initial data 10, a second set of initial data 12, a third set of initial data 14, a fourth set of initial data 16, a fifth set of initial data 18, a sixth set of initial data 20. Each of these sets of initial data correspond to specific experimental conditions. A curve is illustrated for each of these sets of initial data.

The first set of initial data 10 corresponds to a continuous warm light exposure wherein the light sensitivity threshold refers to a just perceptible (JP) discomfort of the initial users. The second set of initial data 12 corresponds to a continuous warm light exposure wherein the light sensitivity threshold refers to a very disturbing (VD) discomfort of the initial users.

The third set of initial data 14 corresponds to a continuous cold light exposure wherein the light sensitivity threshold refers to a just perceptible (JP) discomfort of the initial users.

The fourth set of initial data 16 corresponds to a continuous cold light exposure wherein the light sensitivity threshold refers to a very disturbing (VD) discomfort of the initial users.

The fifth set of initial data 18 corresponds to a blinking warm light exposure wherein the light sensitivity threshold refers to a just perceptible (JP) discomfort of the initial users.

The sixth set of initial data 20 corresponds to a blinking warm light exposure wherein the light sensitivity threshold refers to a very disturbing (VD) discomfort of the initial users.

These sets of initial data are in a system having a logarithmic x-axis representing the illuminance 24 in Lux and y-axis representing the percentile scale 22 in percentage.

Said graph 30 should be used as follows: a quantity representative of a just perceptible discomfort of the user obtained with a continuous warm light exposure is 300Lux corresponds to 30%. It means that 70% of the initial users of the first set of initial data 10 have experienced a just perceptible discomfort at a higher illuminance. As another way to express this result, the light sensitivity of the user belongs to the second decile of the population baseline corresponding to the first set of initial data 10.

When determining the resistance level, a percentage value corresponding to the quantity representative of a light sensitivity threshold of the user in said percentile scale is determined for each quantity of said at least two quantities representative of a light sensitivity threshold of the user. In the example of the graph 30, each quantity representative of a light sensitivity threshold of the user is correlated to a corresponding curve to obtain a percentage value. Said resistance level is then determined depending on said percentage values. Particularly, said resistance level is determined as a combination of said percentage values. This combination may be a mean of these percentage values. A ponderation may also be applied between these quantities, e.g. because of precision of one measurement to another or to taking into account lifestyle.

We can take as an example a first quantity representative of a just perceptible discomfort of the user obtained with a continuous warm light exposure and a second quantity representative of a very disturbing discomfort of the user obtained with a continuous warm light exposure. The first quantity is 300Lux and the second quantity is 500Lux. Using the graph 30 of figure 1, the first percentage value (JP) corresponding to said first quantity is 30% and the second percentage value (VD) corresponding to said second quantity is 20%. The resistance level of the user may be determined as the exact mean between these first (JP) and second (VD) percentage values, i.e. 25%. In an alternative way, a ponderation may be applied to the second percentage value to obtain a resistance level more representative of a very disturbing discomfort. If this ponderation is 2 for the second percentage value, we obtain a resistance level of 27%. The ponderation could also be related to a set of initial data which corresponds to a light exposure which is more frequent for the user and therefore more relevant for determining an ophthalmic product.

This resistance level may be determined as a percentage value, a score or a group. Hence, when the resistance level expressed as a percentage value is 25%, said resistance level expressed as a score may be 2/10 and expressed as a group may be "Low resistance level". Expressing said resistance level as a score or a group makes it easier to figure it out for a user.

Said determining method may comprise the provision of a plurality of resistance level groups based on a resistance level distribution of said population baseline. As an example, we can see on figure 1 that three groups are determined: "low resistance" between 0 and 30% corresponding to a score between 1 and 3, "medium resistance" between 31% and 70% corresponding to a score between 4 and 7 and "high resistance" between 71% and 100% corresponding to a score between 8 and 10. A resistance level group may be determined depending on said resistance level. A filter determining method is further provided to determine at least one filter which fulfills the level of protection required by a user based on an improved determination of the user's sensitivity of light. This filter determining method comprises the above-mentioned resistance level determining method.

By "transparent support", we mean any support through which light may pass and onto which a filter can be disposed to modulate light transmission. The transparent support may be any support intended to be disposed on or in front of an eye of the user. Furthermore, the transparent support may be an ophthalmic lens, a lighting device, an illuminated display, a windshield, a head- mounted display (called "HMD"), a glass, a glass of a portable terminal, etc.

By " filter ", we mean any means able to modulate light, particularly at least one component of the light (see "4D" below). The filter may be a filter coating or a filtering function which can be used to provide a filter coating. The filter may be in the form of a passive filter (uniform, with a gradient or with a spatial variation) or an active filter as photochromic or electrochromic filters.

The level of protection needed by a user can be better defined when considering a determining method which takes into account all these light components to define light environments. The contribution of this definition of the light in the filter determining method is detailed later in this description.

As shown on figure 2, the filter determining method comprises a step 100 of determining a quantity representative of a light sensitivity threshold of the user, a step 200 of determining an index representative of the level of protection required by the user for specific light environments, a step 300 of determining a score for each light environment and for a plurality of filters and a step 400 of determining at least one filter based on the scores determined at step 300.

The light sensitivity determining step 100 comprises the determination of a quantity representative of a light sensitivity threshold of the user. This quantity is preferably an illuminance expressed in lux.

The light sensitivity threshold may be determined based on measurements using a dedicated device. This dedicated device may be device 10 configured to emit light toward one or both eyes of the user, as shown on figure 3. The device 10 is configured to expose the user to an increasing/decreasing light level and to determine the user's light sensitivity threshold based on a user's feedback representative of a discomfort. The light intensity is increased or decreased to form a light varying sequence. Preferably, this sequence comprises increasing light intensity so as to start light emission with a comfortable intensity for the user. The light sensitivity threshold is then determined depending on a response provided by the user. This response may be intentional by asking the user to indicate when a discomfort very disturbing occurs or determined by an external device configured to detect physical response to the user to a given light flux. In both cases, the quantity representative of a light sensitivity threshold of the user may be determined as the illuminance for which a response of the user is detected.

Furthermore, the light sensitivity threshold may be determined for different colors of light to obtain a threshold reflecting cold or warm white light. Emitting light reflecting a cold or warm light, e.g. by emitting more blue light or more red light, allows to respectively simulate substantially artificial or natural light or different light ambiance. Varying light spectrum through modulation of relative proportion various wavelength allows perceived variation of color (and stimulate differently photoreceptors on the retina). Light sensitivity of the user can thus be determined with regard to a variation of the spectral component of the light.

This light sensitivity determining step 100 is for example performed as follows. The device 10 is disposed in front of the eyes of the user and a light source emits a light flux toward the eyes of the user. A measurement sequence is performed comprising three measurement steps. The first measurement step is a continuous light emission to induce an illuminance from a minimum to a maximum values increasing the illuminance by stages, e.g. from 25 Lux to 10211 Lux. For example, the light emission may start with an illuminance of 25 Lux for 5 seconds to adapt the eye to the light condition and cancel all previous light exposure before the measurement and then continue with an increase of the illuminance of 20% each second to the maximum illuminance. In a more general way, the light may be emitted to induce an illuminance varying from 25 Lux to 15000Lux. This first measurement step is performed with warm light. The second measurement step is performed identically to the first measurement step but with cold light.

Then, the third measurement step is a flashing light emission to induce an illuminance from a minimum value to a maximum value increasing the illuminance by stages, e.g. from 25 Lux to 8509 Lux. The illuminance of the flashing light emission is preferably increased by at least 20%, preferably by 40%, most preferably by at least 44%. Before and between each flash light emission, the user is subjected to a light emission lowerthan the minimum value of illuminance of the flashing light emission, e.g. 10 Lux. The time of each flashing light emission is preferably 0,5s and the time between each flashing light emission is preferably 2s.

According to a preferred embodiment, at least one of the first, second and third measurement steps is performed to determine the light sensitivity threshold of the user. A quantity representative of the light sensitivity threshold of the user is thus determined on the basis of the results obtained with at least one of said first, second and third measurement steps. Regarding the definition of light described above, this light sensitivity determining step 100 allows to determine a quantity representative of the light sensitivity threshold with regard to a variation of the intensity, the spatial, the temporal and the spectral components of the light. A global interpretation of the light sensitivity profile of the user may be defined to make the user correspond to a predetermined light sensitivity category, for example from multisensitive to non-sensitive or slighty sensitive. This light sensitivity category is preferably a resistance level group as defined above. As can be seen on figures 4 to 6, these resistance level groups may be "low resistance", "medium resistance" and "high resistance". A high resistance level means that your retina is in good shape. A low resistance level means that you would need more protection in bright conditions to be comfortable.

As shown on figures 4 to 6, results obtained during the light sensitivity determining step 100 may be displayed on a displaying device, as a screen of the computer system. Particularly, these results may comprise at least one light sensitivity threshold determined in at least one of said first, second and third measurement steps. Preferably, each light sensitivity threshold is shown compared to a population baseline to allow the user to see its light sensitivity position based on a light sensitivity baseline from the distribution of the global population. Furthermore, the light sensitivity category determined earlier may also be displayed to inform the user regarding the related issues and providing some recommendations.

As shown on figures 4 to 6, the results are reported to the user in the three light conditions: the warm light, the cold light and the blinking light. A first 50 and a second 52 quantities respectively representative of a just perceptible and a very disturbing discomfort are displayed on each curve of figures 4 to 6.

According to an embodiment, the light sensitivity determining step 100 may comprise a mock step before the first measurement step wherein continuous warm light is emitted toward the user. Alternatively, any light allowing to acclimate the user's with sensation and/or symptoms may be used to have a better reliability. This mock step allows the user to better understand how the device 10 works and acclimate the user's eyes to the light emission of the device 10.

The method also comprises a resistance level determining step 150 using the method detailed above for determining a resistance level. Said resistance level is then preferably displayed on a displaying device. This resistance level determining step 150 may be performed in parallel to the light sensitivity determining step 100. Particularly, said resistance level determining step 150 is preferably performed before the results of the light sensitivity determining step 100 are displayed.

The user index determining step 200 comprises the determination of a user index representative of the level of protection required by the user, for each light environment among a group of light environments.

By "level of protection required by the user", we mean a level of protection based on answers or inputs coming from the user himself, via a questionnaire. Hence, the purpose of this user index determining step 200 is to determine the user's need protection (anamnesis), which kind of light condition does the user face and for which he needs protection. This index determining step 200 thus allows to determine, and potentially select, the light conditions from which the best filter can be chosen.

The light environments are frequent daily situations that can be a source of discomfort for the user. The group of light environments is selected among a set of environments wherein each environment of the set is associated with a given light level with different light components or characteristic (e.g. intensity, spectral, temporal and spatial components). Particularly, the environments of the set are preferably associated with different combinations of light components or characteristic from each other.

According to a preferred embodiment, each light environment is selected to depict a specific combination of the 4D light components (intensity component, spatial component, spectral component and temporal component). Hence, the group as a whole is determined to have the most representative components of the 4D light components gathered in different light environments. We mean by "light environment" a situation which symbolized by means of a picture and/or words a specific light configuration. For instance, a night situation may imply medium to high light intensity (intensity component) with movable light sources (spatial component) which may be only emitted toward the user during a few seconds (temporal component). The group of light environments preferably comprises at least one outdoor situation, at least one indoor situation and at least one night situation. Each light environment may be symbolized either by an image or by a description representative of the situation.

According to a preferred embodiment, the group of light environments comprises five light environments 40 which are shown in figure 7. Each light environment 40 is defined by a level in each of the 4D light components. The higher the level is, the more significant the component is. When the component has no evaluation in a component, this component is meaningless in the light environment.

As shown on figure 7, an image and/or a short description representative of each light environment 40 of the group of environments is provided to the user. In both cases, the image and the description are configured to make the user understand or imagine the light conditions induced by the described light environment 40. The description may be provided to the user either by displaying a text on a displaying device (e.g. a title) and/or via a soundtrack. For each light environment 40, the user is asked to assess the level of discomfort associated to the light environment 40 and/or the recurrence of this light environment 40. By " recurrence ", we mean the frequency at which the user expects to face such a light environment 40.

In a preferred embodiment, questions asked to the user with regard to these light environments 40 are different depending on its light sensitivity. In other words, the user is asked to answer to a first questionnaire if he is considered as a sensitive or highly sensitive user and to a second questionnaire if he is considered as a slightly sensitive or non-sensitive user.

In this preferred embodiment, a slightly sensitive or non-sensitive determining step is performed before the user index determining step 200. Said quantity of light sensitivity threshold of the user is compared to a sensitivity reference to determine if the user is slightly sensitive or non-sensitive.

If the user is determined as sensitive or highly sensitive the first questionnaire may consist in displaying the light environments 40 and ask the user to select the light environments 4 he experiments in his daily life, as shown on figure 7.

If the user is determined as a slightly sensitive or non-sensitive user, the user index determining step 200 is performed using said second questionnaire. This second questionnaire may be specifically adapted to a slightly sensitive or non-sensitive profile. Figure 8 shows an example of said second questionnaire wherein the user is asked for each light environment 40 if he needs to close his eyes, if he blinks and wants to look away and if he doesn't have a problem.

An index 60 representative of the level of protection required by the user is determined based on either the first or the second questionnaire.

Preferably, the user interacts with the computer system to provide his answers. The answers of the user are preferably recorded on a memory of the computer system. The images of the light environments 40 are preferably displayed on the displaying device of the computer system. A discomfort level is then be determined for each light environment 40 of the group depending on the answers of the user.

Then, a score for each light environment 40 and for a plurality of filters is determined at the score determining step 300. As shown on figure 9, the score determining step 300 comprises a step 310 for determining an index representative of the protection provided by a given filter, called the filter index. Each filter of the plurality of filter is at least defined by a filtering ability. According to a preferred embodiment, the filtering ability comprises a luminous transmittance value (Tv) of the given filter. The luminous transmittance (Tv) is a ratio of the luminous flux transmitted by the lens or filter to the incident luminous flux. The luminous transmittance defines the percentage of light from a light flux transmitted through the filter. Hence, a surface with a luminous transmittance of 0 % prevents the whole light flux to pass through the surface whereas a surface with a luminous transmittance of 100 % allows the whole light flux to pass through it without absorbing it.

The luminous transmittance in the visible spectrum may be determined using the equation as follows:

Tv = 100 where

T(A) is the spectral transmittance of the tinted spectacle lens;

V(A) is the spectral luminous efficiency function for daylight (see ISO/CIE 10527);

¾65 _L (Ί) is the spectral distribution of radiation of the illuminant D 65 according to the standard of the International Commission on illumination (see ISO/CIE 10526).

The filter index determining step 310 first comprises a step of determining the filtering ability of each filter of the plurality of filter. Then, the filter index of each filter is determined using the equation as follows: 100

Filter index -

Tv

The filter index thus defines the amount of light cut by the filter. A filter may have a single luminous transmittance value, i.e. a fixed value, or a plurality of luminous transmittance values, as a photochromic or electrochromic lens. In the case where the filter is a varying filter, the lower and higher luminous transmittance values are preferably calculated to determine the compliance of the filter to the user for each lower and higher luminous transmittance values.

The score determining step 300 further comprises a score calculation step 320 for determining the score for each light environment 40 among the group of light environments 40 and for each filter among a group of filters. Said score is representative of the effectiveness of a filter in a given situation, i.e. the ability of a given filter to reach the level of protection required by the user. The score for a given filter and a given light environment 40 is calculated based on the user index in said given light environment 40 and the filter index of said given filter. Particularly, the score is calculated as the ratio between the user index and the filter for said given filter and said given light environment 40. For instance, the score is equal to 1 for a filter index of 6.67 and a user index of 6.67. A score of 1 means that the filter covers 100% of the user's protection needs for said light environment 40. If a filter index is higher than 1, it means that the filter fully protects the user so that light comfort is optimal but there is a risk of vision loss.

The score is therefore a score representative of the compliance for a user of a given filter in a given light environment 40. Providing the score for selected light environment 40 which have been identified by the user as having a high level of discomfort and/or recurrence allows to help determining the best protection for the user.

Then, the filter determining step 400 comprises the determination of at least one filter based on the scores determined at the score determining step 300. This filter determining step 400 aims at ranking the filters based on their scores for the light environments 40. Preferably, the filters are ranked only with regard to the light environments selected by the user.

Each score is associated with a value representative of the compliance of a given filter in a given light environment 40 in view of the level of protection required by the user. Then, a global value may be determined based on all the values determined for a same filter. All the values of a same filter for each light environment 40 or each selected light environment 40 may be added to obtain this global value. The plurality of filters are then ranked based on the global values.

According to a preferred embodiment, one or more filters are determined for at least two transparent supports having different purposes. For example, when the transparent support is an ophthalmic lens, one or more filters are determined for at least two spectacles having different use. One spectacle may be used as sunglasses and another spectacle may be used as everyday eyeglasses. The ranking of the filters is performed with regard to specific light environment which are associated to the use of the transparent support.

According to a preferred embodiment, the closer to 100% the score is, the higher the value is. Particularly, scores from a low compliance threshold to a high compliance threshold may be associated to a positive value whereas scores out of this compliance range may be associated to a negative value. In doing so, the global value of each filter is weighted based on a predetermined degree of compliance to the user's need. For instance, the compliance range may be set from 86% to 200%. Furthermore, scores 50 which are considered to be significantly non-compliant to the user's need, e.g. scores under 50% and above 300%, may be associated to a low value. As an example, scores between 86% and 200% are associated with a value of 2, scores lower than 50% or high than 300% are associated with a value of -2 and scores from 51% to 85% or from 201% to 299% are associated with a value of -0,5. Therefore, if we consider a filter having scores equal to 42, 104, 174, 123 and 185, the respective associated values would be -2, 2, 2, 2 and 2. The global value, i.e. the sum of the values, would be 6. The scores which are summed are at least those which have been selected in the index determining step 200. One or more filters may be then determined to have the best compliance with the user's protection need. Preferably, at least two filters from different categories of filters are determined to provide the user or the ECP with a broader list of compliant filters. Preferably, these different filter categories correspond to different purposes or for different pair of spectacles. Different categories of filter may be filters intended to be put on sunglasses and filters intended to be put on everyday eyeglasses.

As shown on figure 10, an overview of the results of the previous steps may be displayed to the user. This overview may comprise displaying the resistance level group of the user for each light condition. A gaussian diagram 42 may also be displayed showing the resistance level of the user depending on a population baseline. Light protection needs 44 for each light environment 40 and recommended products 46 are also displayed..

As shown on figure 11, one or more ophthalmic products which have been determined as the most compliant with the user's protection needs may be displayed on the displaying device of the computer system. By "ophthalmic product" we mean a filter or a transparent support as described above. Particularly, an information representative of the compliance of each ophthalmic product with regard to each light environment 40 or selected light environment 40 may be displayed. A score of each ophthalmic product may be also determined and optionally displayed for all the selected light environments 40 to give a global performance of each filter. As mentioned above, the filter determining method may be a computer-implemented method which can be performed using code instructions from a computer program product or a computer system. The computer system comprises a processor; and a memory with computer code instructions stored thereon. The memory operatively is coupled to the processor such that, when executed by the processor, the computer code instructions cause the computer system to perform the filter determining method.

In a preferred embodiment, when a resistance level is determined, said population baseline is modified to incorporate said at least two quantities representative of a light sensitivity threshold of the user to obtain a modified population baseline. Then, a resistance level is determined for a next user using said modified population baseline. In doing so, the population baseline is currently updated to make it more accurate. This update may be only partial, i.e. only a portion of the determined quantities are used to determine the modified population baseline.

This update may be performed for a predetermined group of users or users having a same characteristic. This characteristic may be a physical characteristic of the user, e.g. the age or the gender of the user, or a characteristic related to the life of the user, e.g. a geographic area. In this last example, the resistance level may therefore be determined depending on a population baseline corresponding to the country where the user lives.

This update of the population baseline may be described as follows. A first resistance level is determined based on at least two quantities representative of a light sensitivity threshold of a first user using a percentile scale based on a first population baseline. Then, an updated population baseline is determined based on said at least two quantities representative of a light sensitivity threshold of a first user and/or said first resistance level. Finally, a second resistance level is determined based on at least two quantities representative of a light sensitivity threshold of a second user using a percentile scale based on said updated population baseline. This update may be iterated a plurality of times to improve the accuracy of the population baseline. As indicated above, this update may be only partial, i.e. a user selection is made with regard to the user onto which the method is performed depending on a predetermined selection parameter.

Said update of the population baseline may be performed using artificial intelligence. In this embodiment, said method may comprise the use of a machine learning algorithm to update or adapt the population baseline with the results obtained when performing the resistance level determining method.

In a preferred embodiment, said device 10 configured to perform said resistance level determining method is a machine learning-based equipment for determining a resistance level.