OPTICAL ELEMENT FOR A DEVICE FOR DETERMINING THE RELATIVE GLOSS OF A MULTIPLE CAPILLARY FIBERS

Abstract

Optical element (10) for a device for determining the relative brightness of a plurality of hair fibers, or more particularly of a strand of hair, in which the optical element (10) comprises a body (2) made of an isotropic material and defines a measurement zone (36) disposed outside the body (2) and forming a measurement surface of the optical element (10).The optical element (10) includes, in particular, a first incident optical surface (20) of the body (2), through which a measurement light beam (30) emitted by a light-emitting unit (12) is able to pass to enter the body (2) of the optical element (10), and a first emergence optical surface (24) of the body (2), through which the measurement light beam (30) from the first incident optical surface (20) is able to pass to exit the body (2) of the optical element (10), and in which the first emergence optical surface (24) is configured so that the measurement light beam (30) emerges in the direction of the measurement zone (36) configured to receive the plurality of hair fibers or, more particularly, a strand of hair. Figure 1.

Description

Title of the invention: OPTICAL ELEMENT FOR A DEVICE FOR DETERMINING THE RELATIVE BRIGHTNESS OF A PLURALITY OF CAPILLARY FIBERS Field of invention

[0001] The present invention relates to an optical element for a device for determining the relative brightness of a plurality of hair fibers and the associated device. Prior art

[0002] In a known manner, document FR2950695 describes a method for measuring the visual appearance of birefringent fibers arranged randomly and regularly. The method comprises the emission of light, the polarization of the light, the illumination of the fiber from the polarized light, the generation of reflection components and finally the observation of said reflection components.

[0003] However, these solutions do not give complete satisfaction.

[0004] Indeed, the solution presented in document FR2950695 is very bulky and does not allow for domestic use.

[0005] The present invention aims to resolve all or part of the drawbacks mentioned above. Statement of the invention

[0006] To this end, the present invention relates to an optical element for a device for determining the relative brightness of a plurality of hair fibers, or more particularly of a lock of hair, in which the optical element comprises a body made of an isotropic material and defines a measurement zone arranged outside the body and forming a measurement surface of the optical element, said optical element comprising: • a first incident optical surface of the body, through which a measuring light beam emitted by a light emitting unit is able to pass to penetrate into the body of the optical element; • a first optical surface of emergence from the body, through which the measurement light beam coming from the first incident optical surface is able to pass to exit the body of the optical element, and in which the first optical surface of emergence is configured so that the measurement light beam emerges in the direction of the measurement zone configured to receive the plurality of hair fibers or more particularly a lock of hair; • a second incident optical surface of the body, through which a diffuse reflection and a specular reflection generated when the plurality of capillary fibers are placed in the measurement area and more particularly at the measurement surface, are able to pass to penetrate into the body; and • a second optical surface of emergence from the body, through which the diffuse reflection and the specular reflection are able to pass to exit the body of the optical element.

[0007] For the purposes of the present invention, the term "capable of passing through" means that at least a portion of the beam passes through the determined surface.

[0008] Advantageously, such an arrangement makes it possible to obtain an optical element that can be easily integrated into a device for determining the relative brightness of hair fibers in which the measurement zone and the unit for measuring the specular reflection and the diffuse reflection are separated by the optical element. This makes it possible to seally isolate the unit for measuring the specular reflection and the diffuse reflection from the medium comprising the measurement zone. In other words, thanks to these arrangements, the measurement device can be integrated into a sealed volume intended to operate in a humid environment, for example a hairbrush generally used in a bathroom.

[0009] By means of the optical element, the measuring light beam coming from the first incident optical surface is thus configured to be reflected by the hair fibers received in the measuring zone in a diffuse reflection and a specular reflection. Furthermore, the greater the specular reflection, the greater the brightness of the hair fibers. Conversely, the greater the diffuse reflection, the less the brightness of the hair fibers.

[0010] Advantageously, such an arrangement also makes it possible to obtain a device for determining the relative shine of hair fibers which is compact and can be integrated into a hairdressing appliance, for example.

[0011] According to one embodiment, the body of the optical element is made of Polymethyl methacrylate otherwise designated by the acronym PMMA.

[0012] According to one embodiment, the body comprises a recess forming a prism and having an optical reflection surface configured to reflect the measuring light beam coming from the light emission unit towards the first optical emergence surface.

[0013] Advantageously, such an arrangement makes it possible to redirect the light flux from the light source towards the measurement zone while limiting the size of the device for determining the relative brightness of hair fibers. Indeed, the light emission unit emitting the measurement light beam in the direction not of the first optical surface of emergence but in the direction of the optical surface of reflection allows the light emission unit to be arranged in such a way as to save space.

[0014] According to one embodiment, the first optical emergence surface is configured so that the measuring light beam which passes through it forms a substantially perpendicular angle with its surface.

[0015] For the purposes of the present invention, the term “substantially perpendicular” means “perpendicular or perpendicular to within 5°”.

[0016] Advantageously, such an arrangement makes it possible to limit parasitic reflections and thus makes it possible to retain the majority of the flux in the measurement zone, and thus to improve the precision of the measurement of the relative brightness of a plurality of hair fibers or more particularly of a lock of hair.

[0017] According to one embodiment, the measuring surface is defined on a plane forming a substantially non-zero angle with the measuring light beam coming from the first emerging optical surface.

[0018] For the purposes of the present invention, the term “substantially non-zero” means “non-zero or non-zero to within 5°”.

[0019] According to one embodiment, the plane of the measuring surface forms an angle substantially equal to 45° with the measuring light beam coming from the first emerging optical surface. Such an arrangement makes it possible to obtain good reflection of the measuring light beam in a diffuse reflection and a specular reflection. For the purposes of the present invention, the term “substantially equal to 45°” means “equal to 45° or equal to 45° to within 5°”.

[0020] According to one embodiment, the first optical emergence surface forms a substantially perpendicular angle with the second incident optical surface.

[0021] For the purposes of the present invention, the term “substantially perpendicular” means “perpendicular or substantially perpendicular to within 5°”.

[0022] Such an arrangement makes it possible to limit parasitic reflections while retaining the majority of the flux coming from the measurement zone, and thus makes it possible to improve the precision of the measurement of the relative brightness of a plurality of hair fibers or more particularly of a lock of hair.

[0023] According to one embodiment, the optical element comprises a first collimation unit distinct from the body and arranged upstream of the first incident optical surface and configured to carry out collimation of the measuring light beam.

[0024] Advantageously, such an arrangement makes it possible to obtain a precisely oriented measuring light beam.

[0025] According to an alternative, the optical element comprises a first collimation unit formed by the first incident optical surface and configured to achieve a collimation limitation of the measuring light beam.

[0026] Advantageously, such an arrangement makes it possible to obtain a measuring device having a small footprint.

[0027] According to one embodiment, in order to obtain a first incident optical surface configured to carry out collimation, said first incident optical surface has a convex curvature.

[0028] According to another embodiment, in which the second optical emergence surface has a convex curvature so that the diffuse reflection and the specular reflection arrive substantially perpendicular to this second optical emergence surface.

[0029] Such an arrangement makes it possible to avoid any reflection of the diffuse reflection and the specular reflection. This therefore allows the diffuse reflection measuring unit and the specular reflection measuring unit to respectively obtain an optimized measurement and thus to obtain a better measurement of the relative brightness of a plurality of hair fibers, or more particularly of a lock of hair.

[0030] According to one embodiment, the optical element comprises a light filtering unit disposed between the first incident optical surface and the first emerging optical surface.

[0031] According to another embodiment, the light filtering unit comprises a first diaphragm and a second diaphragm, the combination of the first diaphragm and the second diaphragm being arranged to filter the light beam according to a horizontal and vertical component.

[0032] The invention also relates to a device for determining the relative shine of a plurality of hair fibers, or more particularly of a lock of hair, in which the determination device comprises a measuring device comprising: • a light emitting unit configured to emit a measuring light beam; • an optical element as described above; and • a specular reflection measurement unit configured to measure a specular flux from the second optical emergence surface of the optical element, and • a diffuse reflection measuring unit configured to measure a diffuse flux from the second optical emergence surface, and • a calculation unit arranged to calculate a ratio between a measured specular flux resulting from the specular reflection and a measured diffuse flux resulting from the diffuse reflection.

[0033] Advantageously, such an arrangement makes it possible to ensure the precision of the measurement of relative shine of a plurality of hair fibers.

[0034] According to one embodiment, the optical element is configured to separate a first medium comprising the measurement zone from a second medium comprising the light emission unit as well as the unit for measuring specular reflection and diffuse reflection.

[0035] According to one embodiment, the device for determining the relative brightness of a plurality of hair fibers comprises a protective shell configured to receive the optical element.

[0036] According to one embodiment, the protective shell is configured to hermetically isolate from the external environment all the components of the optical element except the measurement zone and the surface of the body of the optical element in which the measurement surface is inscribed.

[0037] This arrangement makes it possible to protect the components of the optical element from impurities in the measurement zone. For the purposes of the present invention, the impurities can be of any kind, such as dust or micro-particles, for example.

[0038] In other words, the shell and the optical element separate an internal medium comprising the light emitting unit, the specular reflection measuring unit and the diffuse reflection measuring unit from an external medium arranged opposite the measuring area.

[0039] According to one embodiment, the diffuse reflection measuring unit and the specular reflection measuring unit are arranged on the same plane.

[0040] Such an arrangement makes it possible to limit the size of the measuring device.

[0041] According to one embodiment, the diffuse reflection measurement unit is configured to measure the diffuse reflection from the second optical emergence surface having an angle substantially equal to 35° with a normal to the measurement surface.

[0042] For the purposes of the present invention, the term “substantially equal” means “equal to or equal to within 5°”.

[0043] According to one embodiment, there are a plurality of diffuse reflections, each having a different angle with the normal to the measurement surface. Measuring the diffuse reflection having an angle substantially equal to 35° makes it possible to obtain an accurate measurement of said diffuse flux.

[0044] According to one embodiment, the specular reflection measurement unit is configured to measure the specular reflection from the second optical emergence surface having an angle substantially equal to 51° with the normal to the measurement surface.

[0045] According to one embodiment, the light emitting unit is arranged to form a measuring light beam of rectangular section whose length is oriented according to the width of the body of the optical element.

[0046] According to one embodiment, the width of the rectangular section of the measuring light beam is less than 4 mm.

[0047] According to one embodiment, the diaphragm among the first diaphragm and / or the second diaphragm arranged to carry out the filtering of the light beam according to the vertical component has an opening height less than the width of the rectangular section of the measuring light beam.

[0048] According to one embodiment, the diffuse reflection measurement unit and the specular reflection measurement unit are optically isolated from the external environment.

[0049] According to one embodiment, the light emitting unit is a light emitting diode or a vertical cavity surface emitting laser diode otherwise designated by the English acronym VCSEL.

[0050] According to one embodiment, the emission unit is oriented so that the light beam directly defines a substantially perpendicular angle with the first optical emergence surface.

[0051] According to one embodiment, the emission unit is oriented so that the light beam defines a substantially perpendicular angle with the first optical emergence surface after it has been reflected by the optical reflection surface.

[0052] Advantageously, such an arrangement makes it possible to limit parasitic flows and thus to improve the measurement of the relative shine of a plurality of hair fibers, or more particularly of a lock of hair.

[0053] According to one embodiment, the filtering unit is optically arranged between the first incident optical surface and the first emerging optical surface.

[0054] According to one embodiment, the filtering unit is optically arranged between the first incident optical surface and the first reflection optical surface.

[0055] According to one embodiment, the outer surfaces of the body of the optical element are made opaque, with the exception of the first incident optical surface, the second incident optical surface, the first emergence optical surface and the second emergence optical surface.

[0056] For the purposes of the present invention, the term “opaque” means “opaque or allowing 10% of the light to pass through”.

[0057] Advantageously, such an arrangement makes it possible to limit parasitic flows and thus to improve the measurement of the relative shine of a plurality of hair fibers, or more particularly of a lock of hair.

[0058] According to one embodiment, the surfaces of the body of the optical element are opacified by black screen printing.

[0059] According to one embodiment, the first diaphragm and the second diaphragm are formed by overmolding material onto the body of the optical element.

[0060] The invention applies to a hairdressing appliance comprising a deter- reduction of the relative shine of a plurality of hair fibers as described above.

[0061] The different aspects defined above which are not incompatible can be combined. Brief description of the figures

[0062] The invention will be even better understood with the aid of the detailed description which is set out below with reference to the appended drawings in which: [Fig.l] [Fig.l] represents a schematic view illustrating the operating principle of a device for determining the relative brightness of a plurality of hair fibers in accordance with the present invention; [Fig.2] [Fig.2] represents a view of an optical element according to a first embodiment in accordance with the present invention; [Fig.3] [Fig.3] represents a sectional view of the optical element of [Fig.2]. [Fig.4] [Fig.4] represents a schematic view of a device for determining the relative brightness of a plurality of hair fibers according to a second embodiment in accordance with the present invention. Description with reference to figures

[0063] [Fig.l] represents a schematic view illustrating the operating principle of a device for determining the relative brightness of a plurality of hair fibers, comprising in particular an optical element 10 for a device for determining the relative brightness of a plurality of hair fibers, or more particularly of a lock of hair, configured to separate a first medium comprising a measurement zone 36 where the plurality of hair fibers are placed, from a second medium containing a light emission unit 12 and light measurement units 40, 42. .

[0064] The optical element 10 comprises a body 2 made of a translucent isotropic material, for example polymethyl methacrylate otherwise designated by the acronym PMMA, defining the measurement zone 36 arranged outside the body 2.

[0065] The optical element comprises a first incident optical surface 20 of the body 2, through which a measuring light beam 30 emitted by a light emitting unit 12 is able to pass to penetrate into the body 2 of the optical element 10. The light emitting unit 12 may be a light emitting diode or a vertical cavity surface emitting laser diode otherwise designated by the English acronym VCSEL.

[0066] This light emission unit 12 is arranged to form a light beam 30 of rectangular section whose length is oriented according to the width of the body 2 of the optical element 10.

[0067] The width of the rectangular section of the measuring light beam 30 is less than to 4 mm.

[0068] As illustrated in the schematic view of [Fig.l], the body 2 of the optical element 10 comprises a recess forming an optical reflection surface 28 configured to reflect the measuring light beam 30 coming from the light emission unit 12 towards a first optical emergence surface 24.

[0069] Thus, the light-emitting unit 12 and the optical reflection surface 28 are oriented so that the measuring light beam 30, after it has been reflected by the optical reflection surface 28, defines a substantially perpendicular angle with the first optical emergence surface 24. Advantageously, such an arrangement makes it possible to redirect the light beam from the light-emitting unit 12 towards the measurement zone 36 while limiting the size of the device for determining the brightness of hair fibers. Indeed, since the light-emitting unit 12 emits the measuring light beam 30 in the direction not of the first optical emergence surface 24 but in the direction of the optical reflection surface 28, this makes it possible to arrange the light-emitting unit 12 in such a way as to save space.

[0070] The first optical emergence surface 24 is configured so that the measurement light beam 30 emerges at a substantially perpendicular angle with its surface in the direction of the measurement zone 36 configured to receive the plurality of hair fibers or more particularly a lock of hair. For the purposes of the present invention, the term “substantially perpendicular” means “perpendicular or perpendicular to within 5°”. Advantageously, such an arrangement makes it possible to limit parasitic reflections and thus makes it possible to improve the accuracy of the measurement of the relative brightness of a plurality of hair fibers or more particularly of a lock of hair.

[0071] According to an embodiment not illustrated, the emission unit 12 is oriented so that the measuring light beam 30 at the output of the emission unit 12 directly defines a substantially perpendicular angle with the first optical emergence surface 24. Such an embodiment makes it possible to dispense with the optical reflection surface 28.

[0072] The first optical emergence surface 24 forms a substantially perpendicular angle with a second incident optical surface 22 onto which a portion of the measurement light beam 30 is reoriented after having reached the plurality of hair fibers, or more particularly the lock of hair arranged on the measurement zone 36. This arrangement of the second incident optical surface 22 relative to the first optical emergence surface 24 makes it possible to limit parasitic reflections while retaining the majority of the flux from the measurement zone 36 leaving for the second incident optical surface 22, and thus makes it possible to improve the accuracy of the measurement of the relative brightness of a plurality of hair fibers or more particularly loosely from a lock of hair.

[0073] The measuring light flux 30 from the measuring zone 36 is broken down into a diffuse reflection 32 and a specular reflection 34 generated when the plurality of hair fibers is placed in the measuring zone 36 and more particularly at the measuring surface. The greater the specular reflection, the greater the brightness of the hair fibers. Conversely, the greater the diffuse reflection, the less brightness of the hair fibers. Advantageously, such an arrangement makes it possible to obtain a compact measuring device that can be integrated into a hairdressing instrument, for example.

[0074] The optical element 10 also comprises a second optical emergence surface 26 of the body 2, through which the diffuse reflection 32 and the specular reflection 34 are able to pass to exit the body 2 of the optical element. For the purposes of the present invention, the term “able to pass through” means that at least a portion of the beam passes through the determined surface.

[0075] The second incident optical surface 22 may also have a concave surface so as to reorient the part of the measuring light beam 30 coming from the measuring zone 36 towards this second optical emergence surface 26 of the body 2.

[0076] Such a configuration therefore allows the optical element 10 to separate the first medium comprising the measurement zone 36 from the second medium comprising the light emission unit 12 as well as the specular reflection measurement unit 42 and diffuse reflection measurement unit 40. Advantageously, such an arrangement makes it possible to obtain a device for determining the relative brightness of hair fibers in which the measurement zone 36 and the specular reflection measurement unit 42 and diffuse reflection measurement unit 40 are separated by the optical element 10. This makes it possible to isolate in a sealed manner the specular reflection measurement unit 42 and the diffuse reflection measurement unit 40 from the medium comprising the measurement zone 36. In other words, thanks to these arrangements, the measurement device can be integrated into a sealed volume intended to move in a humid environment, for example a hairbrush generally used in a bathroom.

[0077] The diffuse reflection measuring unit 40 and the specular reflection measuring unit 42 are arranged on the same plane, which makes it possible to limit the size of the measuring device. The diffuse reflection measuring unit 40 is configured to measure the diffuse reflection 32 coming from the second optical emergence surface 26 having an angle substantially equal to 35° with a normal to the measuring surface. For the purposes of the present invention, the term “substantially equal” means “equal to or equal to within 5°”. According to one embodiment, there are a plurality of diffuse reflections, each having a different angle with the normal to the measuring surface. Measuring the diffuse reflection having an angle substantially equal to 35° allows to obtain an accurate measurement of diffuse reflection 32.

[0078] The specular reflection measuring unit 42 is configured to measure the specular reflection 34 coming from the second optical emergence surface 26 having an angle substantially equal to 51° with the normal to the measuring surface. Such an arrangement makes it possible to obtain a precise measurement of the specular flux.

[0079] According to one embodiment, the second optical emergence surface 26 is curved so that the specular reflection 42 and the diffuse reflection 40 which passes through it form a substantially perpendicular angle with said optical emergence surface 26.

[0080] More precisely, the second optical emergence surface 26 has a convex curvature so that the diffuse reflection 32 and the specular reflection 34 arrive substantially perpendicular to this second optical emergence surface 26.

[0081] The measuring surface is defined on a plane forming a substantially non-zero angle with the measuring light beam 30 coming from the first emerging optical surface 24. For the purposes of the present invention, the term “substantially non-zero” means “non-zero or non-zero to within 5°”. Such an arrangement allows the plane of the measuring surface to form an angle substantially equal to 45° with the measuring light beam 30 coming from the first emerging optical surface 24. Such an arrangement makes it possible to obtain good reflection of the measuring light beam 30 in diffuse reflection and specular reflection. For the purposes of the present invention, the term “substantially equal to 45°” means “equal to 45° or equal to 45° to within 5°”.

[0082] As illustrated more particularly in Figures 2 and 3, the optical element 10 comprises a collimation unit 44 formed by the first incident optical surface 20 and configured to perform collimation of the measurement light beam 30. Advantageously, such an arrangement makes it possible to obtain an optical element 10 and therefore a measurement device having a more limited size. In order to obtain a first incident optical surface 20 configured to perform collimation, said first incident optical surface 20 has a convex curvature.

[0083] According to an alternative as shown in [Fig.4], the device for determining the relative brightness of a plurality of hair fibers, or more particularly of a lock of hair, comprises a collimation unit 44 separate from the body 2 and arranged upstream of the first incident optical surface 20 of the body 2 of the optical element 10, and configured to carry out a collimation of the measurement light beam 30. Advantageously, such an arrangement makes it possible to obtain a precisely oriented measurement light beam 30.

[0084] The body 2 of the optical element 10 forms a light filtering unit 38, op tically arranged between the first incident optical surface 20 and the first emerging optical surface 24; and thus makes it possible to limit parasitic flows and to improve the measurement of the relative brightness of a plurality of hair fibers, or more particularly of a lock of hair.

[0085] More specifically, in the embodiment presented, the light filtering unit 38 is optically disposed between the first incident optical surface 20 and the first reflecting optical surface 28.

[0086] The light filtering unit 38 comprises a first diaphragm 38a and a second diaphragm 38b both arranged in the path of the measuring light beam 30.

[0087] In the embodiment presented, the first diaphragm is arranged on an edge of a cavity 3 provided on the body 2 of the optical element 10.

[0088] This first diaphragm 38a has a height less than the width of the rectangular section of the measuring light beam 30. This first diaphragm 38a thus eliminates all the components of the light beam 30 which would diverge too much in the direction of the height of the optical element 10 or width of the rectangular section of the light beam 30.

[0089] The second diaphragm 38b is disposed between the first diaphragm 38 and the reflection surface 28 and is formed by a narrowing 4 across the width of the body 2 of the optical element 10.

[0090] This second diaphragm 38b has a width less than the length of the rectangular section of the light beam 30. This second diaphragm 38b thus eliminates all the components of the light beam 30 which would diverge too much in the direction of the width of the optical element 10 or length of the rectangular section of the light beam 30.

[0091] Also, the external surfaces of the body 2 of the optical element 10 are made opaque, by applying black screen printing, with the exception of the first incident optical surface 20, the second incident optical surface 22, the surface of the cavity 3 opposite the second incident optical surface 22, the first emergence optical surface 24 and the second emergence optical surface 26.

[0092] For the purposes of the present invention, the term “opaque” means “opaque or allowing 10% of the light to pass through”. Advantageously, such an arrangement makes it possible to limit parasitic fluxes and thus to improve the measurement of the relative brightness of a plurality of hair fibers, or more particularly of a lock of hair. The device for determining the relative brightness of a plurality of hair fibers, or more particularly of a lock of hair, also comprises a calculation unit (not illustrated) arranged to calculate a ratio between a measured specular flux resulting from the specular reflection 42 and a measured reflected flux resulting from the diffuse reflection 32. Interestingly, such an arrangement makes it possible to ensure the accuracy of the relative gloss measurement of a plurality of hair fibers.

[0093] The device for determining the relative brightness of a plurality of hair fibers also comprises an opaque overmolding part (not shown) configured to receive the optical element 10. This opaque overmolding part optically isolates the entire optical part 10 with the exception of the zones outside the body 2 of the optical element 10 and the surfaces of the body 2 through which the measurement light beam 30 passes.

[0094] Thus, this overmolding part contributes to forming the first diaphragm 38a and the second diaphragm 38b.

[0095] The overmolding part is also used as a mechanical support for the optical element 10 by being inserted partly into the cavity 3 and at the level of the narrowing 4 of the body 2 of the optical element 10.

[0096] This overmolding part can be made in one or more parts.

[0097] A protective shell enveloping the optical element 10 and the overmolding part is configured to hermetically isolate from the external environment all the components of the optical element 10 except the measurement zone 36. The diffuse reflection measurement unit 40 and the specular reflection measurement unit 42 are also optically isolated from the external environment. This arrangement makes it possible to protect the components of the device for determining the relative brightness of a plurality of hair fibers from impurities in the measurement zone 36. For the purposes of the present invention, the impurities can be of any kind such as micro-particles for example. In other words, the shell and the optical element 10 separate an internal environment comprising the light emission unit 12, the specular reflection measurement unit 42 and the diffuse reflection measurement unit 40 from an external environment in which the measurement zone 36 operates.

[0098] Of course, the invention is not limited to the embodiments shown and described above, but on the contrary covers all variants thereof.

Claims

Claims

1. Device for determining the relative shine of a plurality of hair fibers, or more particularly of a lock of hair, wherein the determining device comprises a measuring device comprising: • a light emitting unit (12) configured to emit a measuring light beam (30); • an optical element (10) comprising a body (2) made of an isotropic material and defines a measurement zone (36) arranged outside the body (2) and forming a measurement surface of the optical element (10), said optical element (10) comprising a first incident optical surface (20) of the body (2), through which a measuring light beam (30) emitted by a light emitting unit (12) is able to pass to penetrate into the body (2) of the optical element (10); said optical element (10) comprising a first optical emergence surface (24) of the body (2), through which the measurement light beam (30) coming from the first incident optical surface (20) is able to pass to exit the body (2) of the optical element (10), and in which the first optical emergence surface (24) is configured so that the measurement light beam (30) emerges in the direction of the measurement zone (36) configured to receive the plurality of hair fibers or more particularly a lock of hair; said optical element (10) comprising a second incident optical surface (22) of the body (2), through which a diffuse reflection (32) and a specular reflection (34) generated when the plurality of capillary fibers are placed in the measurement zone (36) and more particularly at the measurement surface, are able to pass to penetrate into the body (2); and said optical element (10) comprising a second optical emergence surface (26) of the body (2), through which the diffuse reflection (32) and the specular reflection (34) are able to pass to exit the body (2) of the optical element (10) • a specular reflection measuring unit (42) configured to measure a specular flux from the second optical emergence surface (26) of the optical element (10), and • a diffuse reflection measurement unit (40) configured to measure a diffuse flux from the second optical emergence surface (26), and • a calculation unit arranged to calculate a ratio between a measured specular flux from the specular reflection (34) and a measured diffuse flux from the diffuse reflection (32), the optical element (10) being configured to separate a first medium comprising the measurement zone (36) from a second medium comprising the light emission unit (12) as well as the specular reflection measurement unit (42) and the diffuse reflection measurement unit (40).

2. A device for determining the relative brightness of a plurality of hair fibers according to claim 1, wherein the body (2) comprises a recess forming a prism and having an optical reflection surface (28) configured to reflect the measuring light beam (30) from the light emitting unit (12) towards the first optical emergence surface (24).

3. Device for determining the relative brightness of a plurality of hair fibers according to any one of claims 1 to 2, in which the first optical emergence surface (24) is configured so that the measuring light beam (30) which passes through it forms a substantially perpendicular angle with its surface.

4. Device for determining the relative brightness of a plurality of hair fibers according to any one of claims 1 to 3, in which the measuring surface is defined on a plane forming a substantially non-zero angle with the measuring light beam (30) coming from the first emerging optical surface (24).

5. A device for determining the relative brightness of a plurality of hair fibers according to any one of claims 1 to 4, wherein the first emerging optical surface (24) forms a substantially perpendicular angle with the second incident optical surface (22).

6. A device for determining the relative brightness of a plurality of hair fibers according to any one of claims 1 to 5, in wherein the optical element (10) comprises a first collimation unit (44) separate from the body (2) and arranged upstream of the first incident optical surface (20) and configured to carry out collimation of the measuring light beam (30).

7. A device for determining the relative brightness of a plurality of hair fibers according to any one of claims 1 to 5, wherein the optical element (10) comprises a first collimation unit (44) formed by the first incident optical surface (20) and configured to collimate the measurement light beam (30).

8. Device for determining the relative brightness of a plurality of hair fibers according to any one of claims 1 to 7, in which the second optical emergence surface (26) has a convex curvature so that the diffuse reflection (32) and the specular reflection (34) arrive substantially perpendicular to this second optical emergence surface (26).

9. A device for determining the relative brightness of a plurality of hair fibers according to any one of claims 1 to 8, wherein the optical element (10) comprises a light filtering unit (38) disposed between the first incident optical surface (20) and the first emerging optical surface (24).

10. A device for determining the relative brightness of a plurality of hair fibers according to claim 9, wherein the light filtering unit (38) comprises a first diaphragm (38a) and a second diaphragm (38b), the combination of the first diaphragm (38a) and the second diaphragm (38b) being arranged to perform filtering of the light beam according to a horizontal and vertical component.

11. A device for determining the relative gloss of a plurality of hair fibers according to one of claims 1 to 10, wherein the diffuse reflection measuring unit (40) and the specular reflection measuring unit (42) are arranged on the same plane.

12. A device for determining the relative brightness of a plurality of hair fibers according to any one of claims 1 to 11, wherein the diffuse reflection measuring unit (40) is configured to measure the diffuse reflection (32) from the second optical emergence surface (26) having an angle substantially equal to 35° with a normal to the measuring surface.

13. Device for determining the relative brightness of a plurality of hair fibers according to any one of claims 1 to 12, wherein the specular reflection measuring unit (42) is configured to measure the specular reflection (34) from the second optical emergence surface (26) having an angle substantially equal to 51° with the normal to the measuring surface.

14. A device for determining the relative brightness of a plurality of hair fibers according to any one of claims 1 to 13, wherein the light emitting unit (12) is arranged to form a measuring light beam (30) of rectangular section whose length is oriented along the width of the body (2) of the optical element (10).

15. A device for determining the relative brightness of a plurality of hair fibers according to claim 14 wherein the width of the rectangular section of the measuring light beam (30) is less than 4 mm.

16. Device for determining the relative brightness of a plurality of hair fibers according to any one of claims 14 or 15 in its dependence on claim 10, in which the diaphragm among the first diaphragm (38a) and / or the second diaphragm (38b) arranged to carry out the filtering of the light beam according to the vertical component has an opening height less than the width of the rectangular section of the measuring light beam (30).

17. A device for determining the relative brightness of a plurality of hair fibers according to one of claims 14 to 16, wherein the diffuse reflection measuring unit (40) and the specular reflection measuring unit (42) are optically isolated from the external environment.

18. A hairdressing appliance comprising a device for determining the relative shine of a plurality of hair fibers according to any one of claims 1 to 17.

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