FR2708735A1 - Device making it possible to evaluate the effects of light on the skin and its application to detection of pathologies of the skin - Google Patents

Abstract

The invention relates to a colorimeter device (1), in particular for evaluating the effects of light on the human skin, making it possible to carry out direct measurements on a skin region and comprising a pulsed light source (10), a first reflecting enclosure (11), a light guide (14), a second reflecting enclosure (21), electro-optical measurement sensors (28) and optical filters (27) with defined wavelength spectra, arranged on a plate (26) which is removable or in rotation about the axis ( DELTA ) of symmetry of the device so as to allow permutation of filters. The first enclosure (10) may comprise a diffusing screen (12). An electronic reference sensor (30, 31), measuring a fraction of the emitted light energy, is also provided. Application in particular to determine certain pathologies of the human skin.

Description

 The present invention relates to a device for evaluating the effects of light on human skin, and in particular for measuring the colorations induced after exposure to photoactive radiation such as ultraviolet.

 In what follows, the term skin is understood in its most general acceptance: under this name is meant the skin itself (dermis and epidermis) but also any mucous membrane.

 The invention also relates to the application of such a device to the evaluation of certain skin pathologies.

 We will first briefly recall the phenomena involved.

 After exposure to light from human skin, physical effects are manifested by changes in its coloring. In the following seconds, along with the increase in temperature linked to the absorption of energy in the skin layers, a dermal vasodilation leads to a red coloration due to the blood flow under the epidermis, a reflex intended to dissipate heat . Within a few minutes to a few hours, alterations in molecules or macromolecules, by temperature increase or by oxidations induced by free radicals or activated oxygen species, trigger a complex inflammatory phenomenon: known phenomenon under the usual name of "sunburn", ie an erythema accompanied by more or less marked edema.

The erythema results in a red coloration due to the blood flow, by inflammatory vasodilation of the dermal capillaries. In the longer term, and with a more or less marked intensity depending on the photonic energy of the radiation and the subject's skin type, a physiological protective reaction appears, leading to the production of diffusing and absorbing pigments, the melanins, which are The origin of the tan.

 The long-term effects of repeated exposure to the ultraviolet are manifested by an increase in the thickness of the skin, a prelude to an acceleration of the aging of the exposed tissues. On these degenerative, structural and physiological modifications, keratinocyte cancers can appear. In addition, much more quickly, probably associated with other factors, repeated and especially early sunburn in life, are statistically associated with the occurrence of melanocyte tumors. These cancers spread quickly, and therefore have a very poor prognosis. The increased incidence of these melanomas in fair-skinned populations is causing serious public health concern.

 Another pathology results from exposure to light, in the ultraviolet or visible band, by reactions revealing antagonistic structures or activating molecules which become toxic. In parallel with the increase in the incidence of allergic pathologies, there is an increase in cases of photo-allergies, and photo-toxicity reactions, which can be linked to medications or to household, industrial or cosmetic products.

 It is therefore advantageous to have a reliable means of evaluating inflammatory skin reactions, which result in an increase in the red coloration of the skin, resulting from the absorption bands in the green of the hemoglobin, mainly for the purpose of tests allowing advice or therapy.

The complexity of the situations, certain effects manifesting only for particular spectral domains, makes these explorations difficult to analyze, in the absence of an objective rating of the inflammatory effects. It is recognized that erythema best represents the intensity of inflammatory reactions.

 Outside this general framework of inflammatory states, certain physiological or pathological states can also be manifested by changes in the color of the integuments, for example the presence of biologic pigments which are not eliminated is manifested by jaundice, with a greenish coloration of the mucous membranes or the skin, certain intoxications can also reveal specific colorations (cyanosis, methemoglobinemia: specific absorption bands of the combined forms of hemoglobin). The use of a photocolorimeter would therefore make it possible to carry out various colorimetric measurements, and to appreciate the cutaneous, physiological reactions, the pathological states, this by the selection of specific spectral domains of the reflected light.

 There are known complex and expensive spectrometry devices used in industry or in the laboratory. By way of example, mention may be made of the devices described in patents US-A-4,029,085 (De Witt et al.) And US-A-4,267,844 (De Witt et al.). Both relate to single fiber optic spectrometers using a spectrometer. These professional devices are used in medicine. Other devices are used in the field of general spectrometry.

However, the skin or the mucous membranes have peculiarities which limit the use of the apparatuses used in other fields, such as the reprography industries, and in general all the apparatuses not having a standardized light source, or provided with a continuous light source, even of low average power. A rise in temperature by absorption of excitatory light will cause a local vasodilation reaction which distorts the results. Biological variations can induce very slight changes in color,
or be in a narrow spectral range, which implies a high sensitivity
measuring devices, and to operate by limiting stray light. The impé
Sensitivity constraints require the use of spectrophotometers, most often fitted with a fiber optic sensor and require uniform illumination generally using a dlilbricht sphere.

This first type of device is sensitive, but of a high cost and more difficult to handle. In addition, the local pressure of a measuring head can reduce the inflow
capillary blood and attenuate a coloration linked to micro circulation.

 Another indirect approach consists in taking photographs (slides) according to a precise and invariable protocol, for example with a ring flash, and to analyze secondarily by colorimetry all or part of the photographs.

The impossibility of total reproducibility and rigorous standardization means that this method is rarely used. It requires expensive spectrography equipment, and consumes significant time.

A really usable approach should implement a direct type colorimetric method meeting the following requirements:
* Low energy input, in terms of average power, allowing rapid dissipation of the heat resulting from the absorbed light, which can thus have a high instantaneous power
* Very short measurement time, allowing a high instantaneous energy supply, allowing a good sensitivity, and a low sensitivity to parasitic external lightings
* Standardized broad spectrum excitation source, as close as possible to the visible solar continuum
* Automated compensation for excitation source power deviations
* Independence of the positioning effects of the measuring head
* No direct pressure from the measuring device on the measuring area
* Small surface of the measurement zone, allowing to increase the number of test zones
* Easy interchangeability of the selection bodies of the spectral measurement domains
* Easy interpretation of results
* hIaniability, portability, low cost.

The present invention sets itself as the main aim of meeting these requirements. To do this, it combines the following elements:
* A light source consisting of a discharge lamp, providing a broad spectrum of light emission, mainly in the visible range.

 * A light guide distributing the light evenly over a reduced measurement area.

 * A measurement head without direct local contact with the measurement area.

 * A device recovering the light reflected by the measurement area, in a maximum opening angle, apart from direct illumination of the source. In a preferred embodiment, this device consists of an enclosure of revolution, more particularly spherical, whose interior surface is diffusing and uniformly reflecting in the spectral range of the measurements, without presenting its own emission, either spontaneous or under the effect of incident radiation.

 * Electro-optical sensors protected from direct light from the source, by an internal diaphragm in the recovery device. The distribution of the reflected light is thus uniform over the sensors.

* An electro-optical sensor dedicated to measuring the light emitted by the source
* An interchangeable and / or removable device for selecting the spectral range of measurement.

* A fast response time measurement device, temporally coupled with the emission of the source
* A device for modifying the parameters of the measurements, as well as the methods of calculating the results, advantageously constituted by a microcomputer assembly
* A low voltage, autonomous power supply device.

 The subject of the invention is therefore a colorimeter, in particular for the evaluation of the effects of light on human skin, comprising a light source generating light energy, means for transmitting this light energy to said measurement area and means making it possible to recover and measure at least part of the energy reflected by said area to be measured; characterized in that the light source comprises a discharge lamp generating a pulse of light energy and a first enclosure with reflecting internal surface, in that the transmission means comprise a light guide with an axis of symmetry substantially perpendicular to the said area to be measured, capturing the light energy reflected inside the first enclosure and transmitting it to said area to be measured so as to ensure uniform lighting of this area and in that the means for recovering and measuring the energy light reflected on said area to be measured are constituted by a non-contacting measurement head comprising a second enclosure with internal reflecting surface and electro-optical measurement sensors receiving the light energy reflected inside the second enclosure , these sensors being protected from direct light from the source.

The invention will be better understood and other characteristics and advantages will appear on reading the description which follows and with reference to the appended figures, and among which:
- Figure 1 is a perspective view of the optical part, without filters, of a colorimeter device according to a preferred embodiment of the invention.

 - Figures 2a and 2b illustrate two alternative embodiments of the light source of the colorimeter device according to the invention.

 - Figure 3 is a schematic vertical section of the optical part, supplemented by sensors and filters.

 - Figures 4a to 4c illustrate two alternative embodiments of the device for illuminating the surface studied.

- Figures 5a and 5b illustrate two variants of optical filter holders that can be implemented in all embodiments of the device according to the invention
- Figures 6a and 6b illustrate the light energy source according to an additional embodiment of a colorimetric device according to the invention.

 - Figure 7 is a block diagram of an example of electronic circuits for measurement, calculation and display that can be implemented in the context of the invention.

 We will now describe, in detail, a colorimeter device according to a preferred embodiment of the invention with reference to Figures 1 to 5b. The colorimetric device will be called in the following colorimeter for reasons of simplicity. The colorimeter 1 comprises a light source assembly, composed of a discharge lamp 10 of elongated shape, preferably a lamp of the Xenon flash type, and of a reflective element 11 directing the light emitted towards a cylindrical light guide 14. L 'reflective element it can possibly be omitted. In this case, the lamp 10 must then be placed at a small distance from the end of the light guide 14, their respective axes of symmetry A and Al being perpendicular.

The reflective element 11 can be produced according to several variants. A first alternative embodiment consists, as illustrated in FIG. 2b, of a semi-cylindrical reflector 1 1 ′, coaxial with the lamp 10, returning part of the flux thereof to the light guide 14, of axis A perpendicular to that of the lamp, in its center.

 A second variant embodiment, illustrated in FIGS. 1, 2a and 3, simple and requiring no adjustment, consists of a sphere 11 whose internal surface is equally diffusing in the spectral range studied, without its own emission, whether or not provided an internal screen 12 also diffusing, in order to prevent direct illumination of the light guide 14 by the lamp 10 placed inside the sphere 11. This arrangement ensures total depolarization of the light coming from the light guide towards the area to be studied, but reduces the efficiency, the lamp no longer emitting directly in the light guide. An advantageous solution consists in using a diffusing sphere 11, as has just been described, the lamp 10 being placed coaxially with the light guide 14 whose end 151 is flush with the surface of the sphere II through an orifice 111 made in this one. The diameter of the sphere will be as small as possible relative to that of the "core" of the light guide 14, the efficiency being all the better the lower their ratio, for the same coefficient of diffuse reflection of the sphere. The sphere It has a second orifice, opposite to the orifice 110, through which the lamp 10 and its connections with the outside can be introduced (not shown).

 The light guide 14 may advantageously consist simply of a cylindrical bar 15 (called "core") made of transparent material in the spectral range to be studied, of relative optical index 77, allowing total refraction on the cylinder of the generatrices. The opening angle is designated in the figure by a (a "= 90 signal n-1). The lateral surface of the bar 15 may be made reflective by metallic deposit 150, or opacified and absorbent, in order to avoid leaks light in its path. In a preferred embodiment, the axis of the light guide is coincident with the main axis A of the device 1, in order to uniformly illuminate the central part of the skin area to be studied 29, without illuminating the edges of the opening 17 of a reflected light collector 21, and this without requiring any element for rectifying the light emitted on the measured area 29. The light guide 14 can also be made up of small diameter guides 151. ..15n, for example based on optical fibers, guides assembled in a beam 141 (cross-section view of FIG. 4c). The light collecting ends are regularly spread over the surface of the sphere containing the lamp 10, as illustrated pat Figure 4a This arrangement has the advantage of better uniformity of illumination of the measurement area, by limiting internal reflections for the same length of light guide, and by less disturbing the operation of the sphere at level of the light collection area. Another variant, shown in FIG. 4b, consists in distributing the collecting ends of the elementary guides along the lamp, for example by including them in a support 153.

 The emitting end 152 of the light guide 14 can be extended by a cylinder 16, as illustrated more particularly by FIG. 3, the internal surface of which is absorbent, or even provided with absorbent grooves or crowns constituting a trap for the rays inclined on the axis, in order to diaphragm the beam of rays F coming from the light guide 14, and to prevent these rays inclined on the axis A from directly reaching the surface of the collector 21 of reflected light. This arrangement is useful if the bar 15 is reflectorized up to its emitting end 152, the limiting angle of refraction a no longer being able to restrict the angular opening of the exit of the light guide. The opening is then limited to the angle y by the cylinder 16.

 The reflected light collector 21 is advantageously constituted by a surface of revolution 210, cylindrical, ellipsoid or preferably spherical, the axis of which coincides with the main axis A of the device. On this surface, an opening 17 covers the measurement area illuminated by the light guide 14.

 In a preferred embodiment, illustrated by FIGS. 1 and 3, the collector being spherical, the opening 17 is circular, resulting from the cutting of a polar cap diametrically opposite to the cap 211 allowing the passage of the light guide 14. On a meridian circle, small openings 20 are made, intended to allow the exit of the light scattered in the collector 21 to the electro-optical measurement sensors 28. These sensors 28 convert light energy into electrical signals usable by measurement circuits which will be explained below. The openings 20 are masked from the direct view of the opening 17, by one or more screens or mask 18. This mask can be produced individually for each opening 20. In a preferred embodiment, for reasons of ease of manufacture, the mask 18 consists of a coaxial circular disc integral with the light guide 14. The diameter of this disc is such that it intercepts any light ray 19 going from the opening 17 towards one of the openings 20 (these rays form a cone between the measurement opening 17 and the circle tangent externally to the orifices 20). It is preferable to limit the diameter of the mask 18 to half the internal diameter of the surface of revolution of the collector 21, at the same meridian plane, in order to reduce unnecessary reflections which reduce the proportion of light received by the orifices of the sensors compared to that collected at the measurement orifice. It is therefore desirable for the openings 20 to be made on a meridian with the smallest possible radius around the passage orifice 211 of the light guide 14. The number of these openings 20 is at least three. However, this number can be higher, if it is desired to have a sufficient number of electro-optical measurement sensors 28 in order to study more finely the spectral distribution of the re-emitted light. However, care must be taken to limit the total area of the openings 20 so as not to disturb the operation of the collector, by taking too much light, which would result in a lack of homogeneity in the intensities or the spectral distributions received by each. For the same purpose, the openings 20 will be arranged in equal divisions of the circle, along their meridian, so as to maintain a symmetry of revolution of the assembly.

 By way of nonlimiting example of the scope of the invention and to fix ideas, in a preferred embodiment illustrated by FIG. 3, the collector 21 is a sphere with an internal diameter of 50 mm, the opening 17 is a circle of diameter 20 mm, the axis of each of the openings 20, parallel to the main axis, is on a circle of radius 10 mm, the openings 20 are circular with a diameter of 5 mm, and three in number, arranged at 1200, the light guide 14 contains a methacrylate bar 15, of diameter 6 mm, surrounded by a protective layer 150 (reflecting on the surface of the bar) of thickness I mm, the mask 18 is a disc of thickness 1 mm, 25 mm in diameter, located in the plane of the equator of 21.

The following surfaces are diffusing, uniformly in the spectral range studied, without presenting their own emission, spontaneously or under the effect of an excitation radiation:
- the internal surface of the collector 21
- the surface of the mask (s) 18, on all their faces
the external surface of the light guide 14, for its portion contained in the collector 21, and
- the external surface of the diaphragm 16
A flat plate 24 is positioned tangentially to the manifold 21, at the orifice 211 for passage of the light guide 14. Opposite the orifices 20, it has orifices 240 of the same diameter and of the same axial arrangement.

Between each pair of orifices 240, a light guide 22, similar to the light guide 14, conducts the light received towards the spectral selection device 27, and towards the electro-optical sensor or sensors 28.

 The electro-optical measurement sensor (s) 28 are intended to supply an electrical signal in relation to the quantity of light received. In a preferred embodiment, for cost reasons, they are advantageously photodiodes with corrected response in the visible spectrum.

 Spectral selection devices 27 are interposed between the guides 22 and the electro-optical measurement sensors 28. They can advantageously be constituted by transmission filters, either narrow band if it is desired to analyze a specific spectral range, or by three-color selection filters, such as a Red / Green / Blue combination, with low areas of overlap.

 These filters are mounted on a holding member 26. According to one embodiment of the invention, this holding member 26 is removable, with a recess 261 making it possible to insert it laterally between flat plates 24 and 25 as illustrated by the Figure 5b. According to another form of the invention, the holding member 26 is movable, pivoting around the light guide 14, either using a manual zipper 265 as illustrated in FIG. 5b, or motorized (according to a variant not shown). n is then provided with a number of locations of optical filters 27 multiple of that of the guides 22, and makes it possible to select at least two combinations of filters. n can be supplemented with a positioning device by elastic pawl 262 positioned in a notch 263 with which the support 26 is provided, and / or automatic recognition, by modification of an electrical circuit informing the control unit on the nature and correct positioning of the filters, device (not shown) produced by optical barrier, fixed or mobile contactors.

The pull tab 265 pivots in the opening 301 made in an external covering 300, ensuring the optical seal. A circular skirt 264, integral with the pivoting filter holder 24, prevents the penetration of light through the slot 301 of the pull tab 265.

 As shown in FIG. 3, a positioning member 25 for the electro-optical measurement sensors 28 is arranged parallel to the plate 24. n may consist of a flat plate hollowed out to position the electro-optical measurement sensors 28 opposite the guides 22. This device is opaque in order to prevent the entry of stray light at the level of the electro-optical measurement sensors 28, electrical insulation if the sensor housing is not at ground potential, or if the sensors 28 must be isolated from each other.

 An electro-optical sensor 30, hereinafter called the reference sensor, measures an aliquot fraction of the light emitted by the lamp 10. Its position in the assembly is not critical, it can be illuminated directly by an orifice 112 made in the light box II from the source 10, or receive the light picked up by a light guide 31 connecting its sensitive surface to a surface receiving a fraction of the light emitted by the lamp 10. Preferably, this sensor will be of the same type as those represented under the reference 28, in particular for reasons of internal electrical capacitances, and of response time, the measurement being carried out on a pulse mode.

 A positioning ring 23 is interposed between the plane of the measurement orifice 17 and the skin surface to be studied 29 and, more generally, the surface of the area to be studied. It can be omitted for the measurement of inert surfaces. However, in the case of use in Dermatology or in Medicine, in general, this device allows to postpone the pressure zone away from the studied zone 29, and not to disturb the micro-circulation of this local zone 29.

 We will now describe a second embodiment of a device according to the invention, and more particularly the production of the light source part.

This embodiment is illustrated by Figures 6a and 6b. FIG. 6a more particularly illustrates the progress of the light rays emitted by the sourcel0. Figure 6b illustrates the same device seen in perspective. As in the embodiment of the variant illustrated in FIG. 2b, the reflector consists of a portion of cylindrical reflector 11a, of axis of symmetry Ar parallel to that AI of the lamp. The axis A1 of the lamp 10 is orthogonal to the axis of symmetry Adu light guide 14, as well as the projection of the axis of revolution of the reflector Il a, but these two axes are spaced a short length d, the lamp 10 is therefore offset from the reflector 11a. The light guide 14 preferably consists of a bundle 141 of optical fibers 15n. The angular opening of the reflector 11a is large (about I60), the rays coming from the lamp no longer satisfy the conditions of the Gauss approximation, but converge in an area around the mean axis A of the light guide 141 , area where the ends of the guides 15n are placed. This reflector 1 off-center can be completed with a reflector 1 lb coaxial with the lamp 10, placed head to tail, open on 1800, on the side of the ends of the guides. This reflector 1 lob returns the light to the reflector 1 1 a, in order to increase the efficiency of the assembly. This variant involves adjusting the positioning of the lamp with respect to the various constituent elements. The radius r of the reflector 1 lb is less than the radius R of the reflector 11a.

 The other elements of the device, according to this second embodiment can be produced in a manner identical to those described for the first mode and there is no need to redefine them further.

 We will now describe more precisely the operation of the device according to the invention with reference to FIG. 7. This FIG. 7 illustrates a possible example, among others, of electronic measurement, calculation and display circuits which can be implemented in the context of the invention. They cannot in any case restrict its scope.

 These circuits typically include a computation unit 100, for example a conventional microprocessor comprising, also conventionally, an arithmetic and logic central unit (CPU) 101, a random access memory (RAM) 102, intended to record programs and data, a read-only memory (ROM) 103, containing sequences of instructions and routines, output input circuits (PIO) 104 and a data bus 105 connecting the different circuits. Other elements necessary for the proper functioning of the microprocessor such as clock, address bus, etc., have not been shown. They are well known to those skilled in the art.

 The microprocessor or, more generally, the computation unit 100 receives data and instructions in particular via a keyboard 120 and an analog-digital converter (ADC) 130. The results are displayed on a screen, for example a crystal screen liquids (LCD) 110. A power supply backup set comprising a mains supply 122, a transformer (TR) 121 and a battery-backed converter 120. This assembly supplies the microprocessor 100 as well as the various other circuits shown in FIG. 7. It also supplies a direct supply voltage V + intended for supplying the electro-optical measurement sensors 28.

 A 5measurement control signal is generated by the input-output circuits 104 of the microprocessor 100. n actuates 160. The operational amplifier 150 has a very high input impedance so as not to disturb the measurements.

 In response to a trigger pulse (Measured signal), each electro-optical measurement sensor 28 is connected in series to a low-leakage capacitor C which will accumulate the charges passing through the sensor 28, under the effect of the lighting. , and whose armatures will therefore present a potential difference proportional to the quantity of light received, correction made of the quantum yields according to the wavelengths. After a waiting period covering this switching time, the lamp 10 is activated.

 To do this, it receives from the input-output circuits 104 a Flash control signal transmitted to appropriate control circuits 140 of the lamp 10. These generate the high voltage supply necessary for the proper functioning of the lamp 10 and when the conditions required for this lamp to function correctly are reached, they transmit to the input-output circuits 104 a signal indicating this state: Spret. The Sflash signal causes the lamp 10 to light up.

 The lamp 10 emits a short duration light pulse, of the order of a millisecond. The exciting light reaches the measurement zone 29, via the light guide 14, and is reflected there towards the collector 21, either specularly or diffuse. After multiple reflections on the diffusing surface of the collector assembly, equal fractions of this reflected light reach the measurement orifices 20, pass through the guides 22, are filtered at 27, and reach the electro-optical measurement sensors 28. At the same time, a portion of the exciting light is measured by the reference sensor 30.

 After a measurement delay of the order of a few milliseconds, each measurement capacitor C is isolated from the electro-optical measurement sensor with which it is associated.

 The differential amplifier 150 with very high input impedance is mounted as a unit gain voltage follower. Its non-inverting input is connected to the insulated armature of the measurement capacitor C. The output of the voltage follower, at low impedance, is connected to an amplifier 160 with adjustable gain. The outputs of these amplifiers are connected to the acquisition inputs 161 of the multiplexer 130 of the analog-digital converter 130 connected to the input-output circuits 104 of the microprocessor 100, which stores the measurement in the random access memory 102 of the computer system.

 The multiplexer 131 also receives on an input S30 the signal coming from the reference electro-optical sensor 30, processed in a similar way to those generated by the electro-optical measurement sensors 28, by a measurement chain (not shown).

 After a series of measurements of the potential differences at the output of the amplifiers 160, and their storage (memory 102), the reset signal SRAz emitted by the processor 100 causes the measurement capacitors C to discharge.

The processing of the measurement information is then carried out by the microprocessor 100, in a conventional manner, using programs stored in the read-only memory 103 and / or in the random access memory 102. The corresponding instructions can be entered by the keyboard 120 or by any other means: floppy drive, etc. (not shown). For example, the following operations can be performed:
- elimination of outliers according to a statistical algorithm
- calculation of the mean and standard deviation of each measurement channel
- transformation by the correlation equation, giving the optical density of the spectral area measured
- specific calculations related to the type of measurement, and for example:
* Red / Green ratio giving an estimate of the degree of erythema
* report (Red + Green + Blue) J Reference, giving an overall reflection coefficient of the surface.

 * Blue / Reference report giving an estimate of the production of eumelanins (zone between 500 and 540 nm), or of bilirubin (450 to 500 nm).

 * these values allow you to enter a multidimensional table providing an estimate of the skin type and its pathophysiological state (erythema, tanning). The classification results are displayed on the system screen.

 * specific band / Reference ratio in the case of a coloration linked to a physiopathological state particularized by one or more determined spectral bands (jaundice).

 Naturally in a conventional manner, it will be necessary to carry out initial calibration phases, phases which may be repeated over time.

This calibration meets three objectives:
* determine the response of the device for an ideally absorbing black standard, determining the baseline of each channel.

 * determine the response of the device for an ideal white diffusing standard, making it possible to calculate the corrective factors for each of the measurement channels in use in three-color analyzer.

 * determine the response of the device for gray diffusing standards, in order to determine the correlation curve between the electrical quantities and the reflections, for each channel. Each correlation curve is kept in a non-volatile memory, to deduce from the electrical measurements the corresponding densities, used for the calculations.

 The basic curve can be determined by placing an opaque and absorbing mask on the measurement orifice 17, and performing a series of measurements without triggering the lamp 10.

 The invention is not limited to only the embodiments precisely described in relation, in particular, to FIGS. 1 to 7. although it finds a particularly interesting application in the field of the evaluation of the effects of light on the skin and the determination of certain pathologies, it can also be implemented in other fields of physics, for the measurement of the light reflected by zones of small surface.

Claims (14)

 1. Colorimeter device, in particular for the evaluation of the effects of light on human skin, comprising a light source (10-12) generating light energy, means (14) for transmitting this light energy to said measurement area (29) and means (20-28) for recovering and measuring at least part of the energy reflected by said area to be measured (29); characterized in that the light source comprises a discharge lamp (10) generating a pulse of light energy and a first enclosure with internal reflecting surface (I 1, III, 11a, IIb), in that the means for transmission comprise a light guide (14) of axis of symmetry (/ \) substantially perpendicular to said area to be measured (29), capturing the light energy reflected inside the first enclosure and transmitting it to said area to be measured (29) so as to ensure uniform illumination of this area and in that the means for recovering and measuring the light energy reflected on said area to be measured (29) consist of a measurement head without contact with it ci comprising a second enclosure with an internal reflecting surface (21) and electro-optical measurement sensors (28) receiving the light energy reflected inside the second enclosure (21), these sensors being protected from lt direct light from the source (11, 1 1 ', l la, 1 lb).  2. Device according to claim 1, characterized in that the first enclosure (11) is a spherical enclosure of revolution inside which is disposed the discharge lamp (10).  3. Device according to claim 1, characterized in that the first enclosure (11 ') is a semi-cylindrical enclosure of revolution inside which the discharge lamp (10) is arranged so that, the discharge lamp (10) having an elongated shape around an axis of symmetry (AI), this axis of symmetry is coincident with the axis of the enclosure (11 ') of semi-cylindrical shape.  4. Device according to claim 1, characterized in that the first enclosure consists of first (1 la) and second (1 lb) cylinder portions, internal reflecting surfaces and parallel axes of symmetry, placed head to tail, between which is disposed the discharge lamp (10) so that the latter, having an elongated shape around an axis of symmetry (A1), this axis of symmetry is coincident with the axis of symmetry (A1) from the first cylinder portion (1 la) and at a determined distance (d) from the axis of symmetry of the second cylinder (1 lb) and inside the first cylinder portion (1 la), in that the axis of symmetry (A) of the light guide (14) is perpendicular to the axes of symmetry of the first and second cylinder portions, and in that the radius (R) of said first cylinder portion (1a) is greater to the radius (r) of said second portion of cylinder (I lb) and the entry face (151) of the guide light (14) is flush with the surface of the second cylinder (1 lb), the latter being centered on the axis of symmetry (A) of the light guide, so that the region of convergence of rays of energy reflected by the reflecting surfaces is substantially included in the surface of the diopter formed by the entry face (151) of the light guide (14).  5. Device according to any one of claims 1 to 4, characterized in that the first reflecting enclosure (11) is optically coupled to an electro-optical sensor (30, 31) measuring an aliquot fraction of the light energy emitted by the discharge source (10) so as to serve as a reference.  6. Device according to claim 1, characterized in that the light guide (14) comprises a cylindrical bar (15) made of glass.  7. Device according to claim 6, characterized in that the bar (15) is provided with a layer (150) of external metallization.  8. Device according to claim 1, characterized in that the light guide (14) comprises a bundle (141) of optical fibers (15n).  9. Device according to claim I, characterized in that the second reflecting enclosure (21) is a spherical enclosure of revolution into which the exit face of the light guide (14) opens and to which the sensors are optically coupled electro-optical measurement (28), these sensors (28) being arranged symmetrically around the axis of symmetry (A) of the guide (I 4).  10. Device according to claim 9, characterized in that the electro-optical measurement sensors (28) are arranged on a plate arranged outside the second reflective enclosure (21) and are optically coupled thereto to the using light guides (22).  11. Device according to any one of claims 1 to 10, characterized in that the electro-optical measurement sensors are each associated with at least one optical filter (27) transmitting a spectrum of determined wavelengths.  12. Device according to claim 11, characterized in that the optical filters (27) associated with the electro-optical measurement sensors (28) are arranged on a removable support (26) comprising an opening (261) into which the guide (14).  13. Device according to claim 11, characterized in that the filters associated with the electro-optical measurement sensors (28) are arranged on a support movable in rotation about an axis coincident with the axis (A) of the light guide (14), the total number of optical filter filters (27) being an integer multiple of the number of electro-optical measurement sensors (28) so as to associate with these sensors optical filters with different optical characteristics depending on the position angle of the support (26).  14. Device according to any one of claims 1 to 13, characterized in that it is applied to the determination of pathologies of human skin.