METHOD FOR ILLUMINATION AND SYSTEM FOR DETERMINING A SPECTRAL DISTRIBUTION OF LIGHT FOR ILLUMINATION

Abstract

A method for illuminating an object (200) to be observed and the background, the method comprising the steps of: determining a color matching function and obtaining an xy color value diagram using the color matching function; obtaining a relationship between wavelength and spectral radiance of the object (200) to be observed while the object (200) to be observed and the background are illuminated by a first light source emitting light having an average color rendering index of 40 or more, a color temperature in the range of 3000 K to 10000 K and a continuous spectrum in the wavelength range of 380 nanometers and 780 nanometers; and determining a representative wavelength value corresponding to a local maximum value of the spectral radiance of the object (200) to be observed plotted against the wavelength; and selecting the wavelength.which is closest to the complementary wavelength of the single representative wavelength value in the xy color value diagram, as a reference wavelength value, and illuminating the object to be observed (200) and the background with the light of the representative wavelength value and light of the reference wavelength value.

Description

Technical FieldThe present invention relates to a method of illumination and a system for determining / determining a spectral distribution of light for illumination used to increase the visibility of an object to be observed.Background ArtIn several cases of medical field diagnosis, product inspection in the manufacturing industry, and the like, objects are observed while being illuminated with light for illumination. In such cases, it is preferable to select light for illumination that increases the visibility of objects to be observed. Conventionally, after many attempts and errors, individual observers have selected light for illumination that increases the visibility of objects to be observed based on their personal observations.JP 2014-135 195 A discloses a method in which light for illumination is efficiently used by controlling a spectral distribution of the light for illumination and spectral reflection of color material, and an illumination system using the method. However, JP 2014-135 195 A does not disclose how to determine light for illumination that increases the visibility of objects to be observed.A method of illumination and a system for detecting a spectral distribution of light for illumination that increases the visibility of objects to be observed without the aid of individual observer's own observations and without attempts and errors have not been developed yet.DE 11 2014 005 132 T5 discloses a dimmable solid state lighting device comprising a plurality of LED segments and an LED segment selection circuit, wherein the LED segment selection circuit is configured to selectively control current through the plurality of LED segments to shift the light emitted from the device towards the predetermined spectral energy distribution in response to a dimming input. US 2016 / 0 227 626 A1 discloses a method for determining a spectral power distribution of a light source. JP 2013-246 961 A discloses a lighting device.SUMMARY OF THE INVENTIONProblem to be Solved by the InventionAccordingly, there is a need for a method of illumination and a system for determining a spectral distribution of light for illumination that increases the visibility of objects to be observed without the aid of individual observer's own observations and without attempts and errors. The object of the present invention is to provide a method of illumination and a system for determining a spectral distribution of light for illumination which increase the visibility of objects to be observed without the aid of individual observer's own observations and without attempts and errors.means for achieving the objectAccording to the present invention there are provided a method according to claim 1, a method according to claim 2, a method according to claim 3, a method according to claim 5 and a lighting system according to claim 7. Exemplary embodiments are defined in the dependent claims.A method of illumination according to a first exemplary aspect is a method of illuminating an object to be observed and the background. The method includes the steps of: acquiring a color matching function and acquiring an xy chromaticity diagram (xy chromaticity diagram / xy chromaticity diagram) using the color matching function; acquiring a relationship between wavelength and spectral irradiance of the object to be observed while the object to be observed and the background are illuminated by a first light source that emits light having an average color rendering index of 40 or more, a color temperature in the range of 3000 K to 10000 K, and a continuous spectrum in the wavelength range of 380 nanometers and 780 nanometers; and acquiring a value of a representative wavelength corresponding to a maximum value of the spectral irradiance of the object to be observed plotted against the wavelength or values of a representative wavelength, corresponding to maximum values of the spectral radiation density of the object to be observed plotted against the wavelength, obtaining a value of a comparative wavelength for the value or values of the representative wavelength using the value or values of the representative wavelength and the xy chromaticity diagram so as to increase a contrast ratio between the object to be observed and the background, and illuminating the object to be observed and the background with the light of the value or values of the representative wavelength and light of the value of the comparative wavelength.In the illumination method according to the present aspect, the value of the comparative wavelength for the value or values of the representative wavelength is obtained using the value or values of the representative wavelength and the xy chromaticity diagram, so as to increase a contrast ratio between the object to be observed and the background. Accordingly, the visibility of the objects to be observed can be increased without the aid of own observations from individual observers and without attempts and errors.In the illumination method according to a first embodiment of the first aspect, a stop band of the comparison wavelength is determined before the value of the comparison wavelength is obtained, and the value of the comparison wavelength is determined such that the value is outside the stop band.According to the illumination method according to the present embodiment, a color taste of an observer can be taken into account by detecting the blocking zone of the comparison wavelength in an image.In the illumination method according to a second embodiment of the first aspect, in the step of acquiring the comparison wavelength, a single value of the representative wavelength is used, and the wavelength closest to the complementary wavelength of the single value of the representative wavelength in the xy chromaticity diagram is selected as the value of the comparison wavelength.According to the illumination method according to the present embodiment, the contrast ratio between the object to be observed and the background can be increased by selecting the complementary wavelength of the value of the representative wavelength in the xy chromaticity diagram as the value of the comparative wavelength.In the illumination method according to a third embodiment of the first aspect, in the step of acquiring the value of the comparison wavelength, a plurality of values of the representative wavelength are used, and the wavelength corresponding to the point at which a sum of color differences from the plurality of points representing the plurality of values of the representative wavelength in the xy chromaticity diagram is maximized is selected as the value of the comparison wavelength.According to the illumination method according to the present embodiment, the contrast ratio between the object to be observed and the background can be increased by selecting the wavelength corresponding to the point at which a sum of color differences from the plurality of points representing the plurality of values of the representative wavelength is maximized in the xy chromaticity diagram as the value of the comparison wavelength.In the illumination method according to a fourth embodiment of the first aspect, in the step of acquiring the value of the comparison wavelength, a plurality of values of the representative wavelength are used, and in the xy chromaticity diagram, the wavelength closest to the complementary wavelength of the average of the plurality of values of the representative wavelength in the xy chromaticity diagram is selected as the value of the comparison wavelength.According to the illumination method according to the present embodiment, the contrast ratio between the object to be observed and the background can be increased by selecting, in the xy chromaticity diagram, the wavelength closest to the complementary wavelength of the average of the plurality of values of the representative wavelength selected as the value of the comparative wavelength.A method of illumination according to a second exemplary aspect is a method of illuminating an object to be observed and the background. The method includes the steps of: acquiring a relationship between wavelength and spectral irradiance of the object to be observed while the object to be observed and the background are illuminated by a first light source emitting light having an average color rendering index of 40 or more, a color temperature in the range of 3000 K to 10000 K, and a continuous spectrum in the wavelength range of 380 nanometers and 780 nanometers; and obtaining a value of a representative wavelength corresponding to a maximum value of the spectral irradiance of the object to be observed plotted against the wavelength or values of a representative wavelength corresponding to a maximum value of the spectral irradiance of the object to be observed plotted against the wavelength, acquiring a relationship between wavelength and spectral irradiance of the background while the object to be observed and the background are illuminated by the first light source, and acquiring a value of a comparison wavelength corresponding to a maximum value or a minimum value of the spectral irradiance of the background plotted against the wavelength or values of a comparison wavelength corresponding to maximum values or minimum values of the spectral irradiance of the background plotted against the wavelength, and illuminating the object to be observed and the background with the light of the value or values of the representative wavelength and light of the value or values of the comparison wavelength.In the illumination method according to the present aspect, the relationship between wavelength and spectral irradiance of the object to be observed is obtained while the object to be observed and the background are illuminated by the first light source, the value of a representative wavelength corresponding to a maximum value of the spectral irradiance of the object to be observed plotted against the wavelength or the values of a representative wavelength corresponding to maximum values of the spectral irradiance of the object to be observed plotted against the wavelength are obtained, the relationship between wavelength and spectral irradiance of the background is obtained while the object to be observed and the background are illuminated by the first light source, and the value of a comparative wavelength corresponding to a maximum value or a minimum value of the spectral irradiance of the background plotted against the wavelength is obtained, If the values of a comparison wavelength corresponding to maximum values or minimum values of the spectral radiation density of the background plotted against the wavelength are determined and the object to be observed and the background are illuminated with the light of the value or the values of the representative wavelength and light of the value or the values of the comparison wavelength. Accordingly, the value or values of the comparison wavelength can be determined for the value or values of the representative wavelength, such that the contrast ratio between the object to be observed and the background is increased. The visibility of the object to be observed can thus be increased without the aid of own observations by individual observers and without attempts and errors.In the illumination method according to a first embodiment of the second aspect, a blocking zone of the representative wavelength and the comparative wavelength is obtained before the value or values of the representative wavelength and the value or values of the comparative wavelength are obtained, and the value or values of the representative wavelength and the value or values of the comparative wavelength are obtained such that the value or values of the representative wavelength and the value or values of the comparative wavelength are outside the blocking zone.In the illumination method according to the present embodiment, the value or values of the representative wavelength and the value or values of the comparative wavelength can be more easily obtained by detecting the stop band. Furthermore, preferences of an observer can be taken into account by ascertaining the blocking zone.A system for determining / obtaining a spectral distribution of light for illumination according to a third exemplary aspect includes a first light source that emits light having an average color rendering index of 40 or more, a color temperature in the range of 3000 K to 10000 K, and a continuous spectrum in the wavelength range of 380 nanometers and 780 nanometers, a spectral irradiance meter, and a processor connected to the spectral irradiance meter. The system is configured to determine a value or values of a representative wavelength and a value or values of a comparative wavelength according to the method of the first or second aspect.According to the system for obtaining a spectral distribution of light for illumination according to the present aspect, light for illumination can be obtained such that the contrast ratio between the object to be observed and the background is increased.An illumination system according to a fourth exemplary aspect includes the system for determining a spectral distribution of light for illumination according to the third aspect and a second light source for illumination with the determined light for illumination.According to the illumination system according to the present aspect, the visibility of the object to be observed can be increased without the aid of own observations from individual observers and without attempts and errors.In the illumination system according to a first embodiment of the fourth aspect, the second light source is composed of the first light source and a plurality of filters.By using the first light source, the illumination system can be simplified.Brief Description of DrawingsFIG. 1 shows a configuration of an illumination system 100 used for an illumination method according to the present invention, FIG. 2 is a flowchart for describing the method of illumination according to the first aspect of the present invention, FIG. 3 shows the xy chromaticity diagram determined using the chromaticity coordinate function, FIG. 4 shows relative values of spectral irradiation of the xenon lamp without a filter, FIG. 5 is an image showing the object to be observed and the background illuminated by the xenon lamp without a filter, FIG. 6 is a graph representing the spectral radiation density of the region numbered 1 in FIG. 5 in the object to be observed illuminated by the xenon lamp without a filter, FIG. 7 is a graph representing the spectral radiation density of the region numbered 25 in FIG. 5 in the background illuminated by the xenon lamp without a filter, FIG. 8 is a flowchart for describing step S 1040 of FIG. 2 , FIG. 9 is a graph representing the spectral radiation density of the region numbered 1 in FIG. 5 in the object to be observed illuminated with light of the value of the representative wavelength (470 nanometers) and light of the value of the comparative wavelength (560 nanometers), FIG. 10 is a graph representing the spectral radiation density of the region numbered 25 in FIG. 5 in the background illuminated with light of the value of the representative wavelength (470 nanometers) and light of the value of the comparative wavelength (560 nanometers), FIG. 11 is an image showing the object to be observed and the background illuminated with light of the value of the representative wavelength (470 nanometers) and light of the value of the comparative wavelength (560 nanometers), FIG. 12 is a graph representing the spectral radiation density of the region numbered 1 in FIG. 5 in the object to be observed illuminated by the xenon lamp without a filter, FIG. 13 is a graph representing the spectral radiation density of the region numbered 25 in FIG. 5 in the background illuminated by the xenon lamp without a filter, FIG. 14 is an image showing the object to be observed and the background illuminated by the xenon lamp without a filter, FIG. 15 shows an xy chromaticity diagram determined using a chromaticity coordinate function, FIG. 16 is a flowchart for describing step S 1040 of FIG. 2 when two wavelength values are selected as the values of the representative wavelength, FIG. 17 shows an xy chromaticity diagram determined using a chromaticity coordinate function, FIG. 18 shows a spectral radiation density distribution of an object to be observed illuminated by the first light source, FIG. 19 shows a spectral radiation density distribution of the background illuminated by the first light source, FIG. 20 shows an image of the object to be observed and the background illuminated by the first light source, FIG. 21 shows an image of the object to be observed and the background illuminated by the second light source emitting the light of the representative wavelength and the comparative wavelength in the additional example of the first aspect of the present invention, FIG. 22 is a flowchart for describing the method of illumination according to the second aspect of the present invention, FIG. 23 shows a spectral radiation density distribution of an object to be observed illuminated by the first light source, FIG. 24 shows a spectral radiation density distribution of the background illuminated by the first light source, FIG. 25 shows an image of the object to be observed and the background illuminated by the second light source emitting the light of the representative wavelength and the comparative wavelength in the first example of the second aspect of the present invention, FIG. 26 shows a spectral radiation density distribution of an object to be observed illuminated by the first light source, FIG. 27 shows a spectral radiation density distribution of the background illuminated by the first light source, FIG. 28 shows an image of the object to be observed and the background illuminated by the second light source emitting the light of the representative wavelength and the comparative wavelength in the second example of the second aspect of the present invention, FIG. 29 shows a spectral radiation density distribution of an object to be observed illuminated by the first light source, FIG. 30 shows a spectral radiation density distribution of the background illuminated by the first light source; and FIG. 31 shows an image of the object to be observed and the background illuminated by the second light source emitting the light of the representative wavelength and the comparative wavelength in the third example of the second aspect of the present invention.DESCRIPTION OF EMBODIMENTSFIG. 1 shows a configuration of a lighting system 100 used to perform a lighting method according to the present invention. The illumination system 100 includes a light source subsystem 110, a two-dimensional spectral irradiance meter 120, and a processor 130. The light source subsystem 110 includes a plurality of light sources 111 used with replaceable filters, light guides 113, and a projector 115. Light for illumination having a desired wavelength is generated by the plurality of light sources 111 used with replaceable filters and transmitted via the light guides 113 to the projector 115 which illuminates an object with the light for illumination. Generally, a light source emitting light having the following features should be employed. The light has an average color rendering index (Ra) of 40 or more, a color temperature in the range of 3000 K to 10000 K, and a continuous spectrum in the wavelength range of 380 nanometers and 780 nanometers. A light source having the above-described features is referred to as a first light source. The first light source may be, for example, a xenon lamp, a metal halide lamp, a mercury lamp, a halogen lamp, a white LED (Light Emitting Diode), and the like. Each of the plurality of light sources 111 used with replaceable filters is a combination of the first light source and one of the replaceable filters. For example, each of the plurality of filters is configured to transmit light having a determined wavelength value, and the determined values are at 10-nanometer intervals. Thus, by appropriately selecting filters of the plurality of light sources 111 used with replaceable filters, the light source subsystem 110 functions as a variable spectrum light source. The object 200 is an object to be observed and the background. The two-dimensional spectral irradiance meter 120 measures the spectral irradiance of the object 200 under pre-detected conditions described later. The measured spectral irradiance data of the object 200 is sent to the processor and light for illumination that enhances the contrast between the object to be observed and the background and that enhances the visibility for an observer is determined by the processor 130. The light for illumination thus detected is realized by the plurality of light sources 111 used with replaceable filters. A light source for the illumination light for enhancing visibility thus realized is referred to as a second light source. Generally, the second light source may be a light source separate from the first light source other than a combination of the first light source and filters.A system for detecting a spectral distribution of light for illumination according to the present invention is used to detect the second light source, and includes the first light source, the spectral irradiance meter 120, and the processor 130. The illumination system 100 is a combination of the above-described system for determining a spectral distribution of light for illumination and the above-described second light source.In the following description, a xenon lamp is used as the first light source.FIG. 2 is a flowchart for describing the method of illumination according to the first aspect of the present invention.In step S 1010 of FIG. 2, a color adjustment function for an observer or these are determined for a color sensor of a camera of a machine vision system and the like.First, how to determine a color matching function for an observer will be described. Although individual differences in color perception of white light observers such as sunlight and white LED light can be ignored, individual differences in color perception of white light observers for illumination whose color has been adjusted by metamerism cannot be ignored. Accordingly, it is desirable that a color matching function is obtained for a single observer to increase the visibility specific to the single observer. However, the present step may be omitted when the visibility specific to the single observer can be ignored and the visibility for an average observer is to be increased by enhancing the contrast between an object to be observed and the background, and a standard color matching function may be employed.Next, how to determine a color adjustment function for a color sensor of a camera will be described. Since a color adjustment function for a color sensor of a camera is not available, a color adjustment function for a color sensor of a camera must be prepared.A color matching function is obtained by a color matching experiment. For the color matching experiment, a light source for generating light of a single wavelength and a light source for generating light of a combination of RGB lights of reference color stimulations are prepared. As described above, two light sources including two sets of light source subsystems 110 may be employed. Two adjacent regions of a white screen are separately illuminated with light of a single wavelength and light of a combination of RGB lights of reference color stimulations by a respective one of the two light sources described above, respectively, and the radiation intensity of each of the RGB lights is adjusted using image data captured by the camera, so that colors of the two regions described above are considered to be identical to each other. Values of metamerism for each wavelength are thus determined and the color matching function is defined.In step S 1020 of FIG. 2, an xy chromaticity diagram is obtained using the chromaticity coordinate function obtained in step S 1010 or a standard chromaticity coordinate function. When tristimulus values are expressed by X, Y and Z, colour values (x,y) can be expressed by the following expressions.Values of x and y are obtained by substituting values of the color matching function for each wavelength into the tristimulus values of the terms described above to determine the xy chromaticity diagram.FIG. 3 shows the xy chromaticity diagram determined using the chromaticity coordinate function. How to use the xy chromaticity diagram will be described later.In step S 1030 of FIG. 2, spectral data (spectral irradiance data) of an object to be observed is obtained, and the value or values of the representative wavelength are determined using the spectral data.The spectral data (spectral irradiance data) of the object to be observed is obtained in a state where the object to be observed and the background are illuminated by a xenon lamp without a filter (the first light source).FIG. 4 shows relative values of the spectral radiation intensity of the xenon lamp without a filter. The horizontal axis of FIG. 4 indicates the wavelength, and the unit of the wavelength is nanometers. The vertical axis of FIG. 4 indicates relative values of the spectral radiation intensity.FIG. 5 is an image showing the object to be observed and the background illuminated by the xenon lamp without a filter. The image is divided into 25 regions separated by four horizontal lines and four vertical lines. In FIG. 5, a dark area including the area numbered 1 is the area of the object to be observed, and a light area including the area numbered 25 is the area of the background.FIG. 6 is a graph representing the spectral radiation density of the region numbered 1 in FIG. 5 in the object to be observed illuminated by the xenon lamp without a filter. The horizontal axis of the graph indicates the wavelength and the unit is nanometers. The vertical axis of the graph indicates the radiation density and the unit is watts per steradian per square meter per nanometer.Using the spectral radiation density of the object to be observed shown in FIG. 6, the value of the representative wavelength of the object to be observed is obtained. The wavelength value corresponding to a maximum value of the spectral irradiance may be selected as the value of the representative wavelength. the wavelength values corresponding to maximum values of the spectral irradiance in FIG. 6 are 470 nanometers and 720 nanometers. Either or both of the two wavelength values may be selected as a value or values of the representative wavelength. In the present example, the value of 470 nanometers was selected as the value of the representative wavelength.In step S 1040 of FIG. 2, a value of a comparison wavelength for the value of the comparison wavelength is obtained using the representative wavelength and the xy chromaticity diagram.FIG. 7 is a graph representing the spectral radiation density of the region numbered 25 in FIG. 5 in the background illuminated by the xenon lamp without a filter. The horizontal axis of the graph indicates the wavelength and the unit is nanometers. The vertical axis of the graph is irradiance and the unit is watts per steradian per square meter per nanometer. in FIG. 7, the solid line in the graph represents the spectral irradiance of the area in the background and the dashed line represents the spectral irradiance of the area in the object to be observed. The spectral radiation density of the region in the object to be observed is identical to that shown in Fig. 6.Provided that the background is colorless or achromatic color (white or gray), a spectral distribution of light for illumination that maximizes the contrast between the object to be observed and the background is determined by a product of light of the value of the representative wavelength and light of the complementary wavelength corresponding to the complementary color of the color corresponding to the value of the representative wavelength. Accordingly, it would be appropriate to select the complementary wavelength corresponding to the complementary color of the color corresponding to the value of the representative wavelength as the value of the comparison wavelength for enhancing the contrast between the object to be observed and the background.On the other hand, some observers using the method of illumination may wish to adjust the color of the background. For example, the wavelength range equal to or greater than 570 nanometers may be defined as a blocking zone Z of the wavelength when the user desires to reduce redness in the background.FIG. 8 is a flowchart for describing step S 1040 of FIG. 2.In step S 2010 of FIG. 8, the point A corresponding to the value of 470 nanometers of the representative wavelength on a spectral color train is determined in the xy chromaticity diagram shown in FIG. 3. The spectral color trace is the curve forming the outer periphery of the xy chromaticity diagram.In step S 2020 of FIG. 8, the straight line AW connecting the point A and the white point W is obtained in the xy chromaticity diagram shown in FIG. 3.In step S2030 of FIG. 8, the intersection point B between the straight line AW and the spectral color train is obtained. The point B is the point corresponding to the complementary color of the color corresponding to the value of the representative wavelength. Further, the point B is located at the position where the color difference from the point A corresponding to the value of 470 nanometers of the representative wavelength is maximized.In step S2040 of FIG. 8, a zone Z corresponding to a stop zone of the comparison wavelength is detected in the xy chromaticity diagram shown in FIG. 3.In step S 2050 of FIG. 8, a point C is located on the spectral color train and outside the zone Z, so that an angle θ formed by the straight line AB and the straight line AC is minimized in the xy chromaticity diagram shown in FIG. 3. The wavelength value corresponding to the point C is then selected as the value of the comparison wavelength. The wavelength value corresponding to the point C is not in the cut-off zone Z of the wavelength and is closest to the complementary wavelength of the value of the representative wavelength. In this example, the target wavelength values of the filters are at 10-nanometer intervals and the value of the representative wavelength is set to 560 nanometers.Further, the spectral color train may be expressed by curve steps with an implicit function when steps S 2010-S 2050 are performed.In step S 1050 of FIG. 2, the object to be observed and the background are illuminated by the second light source, by which light of the value of the representative wavelength (470 nanometers) and light of the value of the comparative wavelength (560 nanometers) are combined.FIG. 9 is a graph representing the spectral radiation density of the region numbered 1 in FIG. 5 in the object to be observed illuminated with light of the value of the representative wavelength (470 nanometers) and light of the value of the comparative wavelength (560 nanometers). The horizontal axis of the graph of FIG. 9 indicates the wavelength and the unit is nanometers. The vertical axis of Figure 9 is the spectral irradiance and the unit is watts per steradian per square meter per nanometer. The horizontal axis and the vertical axis in each of FIGS. 10, 12, and 13 described later are similarly defined.FIG. 10 shows a graph representing the spectral radiation density of the region numbered 25 in FIG. 5, in the background illuminated with light of the value of the representative wavelength (470 nanometers) and light of the value of the comparative wavelength (560 nanometers).FIG. 11 is an image showing the object to be observed and the background illuminated with light of the value of the representative wavelength (470 nanometers) and light of the value of the comparative wavelength (560 nanometers). In FIG. 11, "front" represents the range of the object to be observed, and "rear" represents the range of the background.FIG. 12 is a graph representing the spectral radiation density of the region numbered 1 in FIG. 5 in the object to be observed illuminated with the xenon lamp without a filter.FIG. 13 is a graph representing the spectral radiation density of the region numbered 25 in FIG. 5 in the background illuminated with the xenon lamp without a filter.Fig. 14 is an image showing the object to be observed and the background illuminated by the xenon lamp without a filter. In FIG. 14, "front" represents the range of the object to be observed, and "rear" represents the range of the background.The contrast ratio between the object to be observed and the background in the image shown in FIG. 11 obtained using the method of illumination according to the present invention is 32.8% larger as compared with the contrast ratio between the object to be observed and the background in the image shown in FIG. 14 obtained using a conventional method of illumination. Contrast ratio values are obtained according to JIS (Japanese Industrial Standard). Images in which the contrast between the object to be observed and the background is enhanced for more accurate observation can thus be provided by the method of illumination according to the present invention.Generally, when an illuminated surface is a uniformly reflective diffuser, the spectral irradiance of the surface is the product of the spectral irradiance on the surface and the spectral reflectance of the surface. Accordingly, the visibility of an object can be increased by determining the spectral radiation intensity in consideration of the spectral reflectance of the object.As another example of how a value of the comparative wavelength is obtained when the value of 720 nanometers corresponding to another maximum value of the spectral irradiance shown in FIG. 6 is selected as the value of the representative wavelength will be described below using the flowchart of FIG. 8.FIG. 15 shows an xy chromaticity diagram determined using a chromaticity matching function.In step S2010 of FIG. 8, the point A corresponding to the value of 720 nanometers of the representative wavelength on the spectral color train is found in the xy chromaticity diagram shown in FIG. 15.In step S 2020 of FIG. 8, the straight line AW connecting the point A and the white point is obtained in the xy chromaticity diagram.In step S2030 of FIG. 8, the intersection point B between the straight line AW and the spectral color train is obtained. The point B is the point corresponding to the complementary wavelength of the value of the representative wavelength.In this example, a zone Z corresponding to a stop zone of the comparison wavelength is not provided, and the wavelength corresponding to the point B is selected as the value of the comparison wavelength. The value of the reference wavelength is 490 nanometers.Still another example of how to obtain a value of a comparative wavelength when the wavelength values of 470 nanometers and 720 nanometers corresponding to the two maximum values of the spectral irradiance shown in FIG. 6 are selected as the values of the representative wavelength will be described below.FIG. 16 is a flowchart for describing step S 1040 of FIG. 2 when two wavelength values are selected as the values of the representative wavelength.FIG. 17 shows an xy chromaticity diagram determined using a chromaticity matching function.In this example, the segment of the spectral color train between the two points representing the two wavelength values corresponding to the two maximum values of the spectral radiation density surrounds the white point in the xy chromaticity diagram shown in FIG. 17. In other words, the angle of view is greater than 180 degrees when the segment of the spectral color trace between the two points representing the two wavelength values is observed from the white point.In step S3010 of Fig. 16, the point A and the point A' corresponding respectively to the value of 720 nanometers and the value of 470 nanometers of the representative wavelength are obtained in the xy chromaticity diagram shown in Fig. 17.In step S3020 of Fig. 16, the straight line AW connecting the point A and the white point W and the straight line A'W connecting the point A' and the white point W are obtained in the xy chromaticity diagram shown in Fig. 17.In step S3030 of Fig. 16, the intersection point P between the straight line AW and the spectral color train and the intersection point P' between the straight line A'W and the spectral color train in the xy chromaticity diagram are obtained. In the segment of the spectral color train between the point P and the point P' in the xy chromaticity diagram, there exists a point corresponding to a wavelength value that increases the visibility for the two wavelength values.In step S3040 of FIG. 16, a point moving on the spectral color train between the point P and the point P' in the xy chromaticity diagram shown in FIG. 17 is defined as a point C, and when the point C maximizes the sum of the length of the line segment PC and the length of the line segment PC', the point C is defined as the point B. The wavelength value corresponding to the point B is selected as the value of the comparison wavelength. The wavelength value corresponding to the point B is 515 nanometers. The point B substantially corresponds to the point at which the sum of the color difference from the point A and the color difference from the point A' is maximized. In this example, the target wavelength values of the filters are at 10-nanometer intervals and the value of the comparative wavelength is set to 520 nanometers.When three or more wavelength values are selected as the values of the representative wavelength, the value of the comparative wavelength can be obtained in a similar manner.When distances between the plurality of points on the spectral color train in the coordinate plane are 0.1 or smaller, the points representing a plurality of wavelength values, substantially identical results can be obtained even when the average value of the plurality of wavelength values is selected as the value of the comparative wavelength in the flowchart shown in FIG. 8.An additional example of the illumination method according to the first aspect of the present invention will be described below.FIG. 18 shows a spectral radiation density distribution of an object to be observed illuminated by the first light source (the xenon lamp without a filter). The horizontal axis in Fig. 18 indicates the wavelength, and the vertical axis in Fig. 18 indicates the spectral radiation density.In accordance with step S1030 of FIG. 2, the value of 550 nanometers from a maximum value of the spectral irradiance shown in FIG. 18 is selected as the value of the representative wavelength. In accordance with step S1040 of FIG. 2 and the flowchart of FIG. 8, the value of 430 nanometers is then selected as the value of the comparative wavelength for the background. Further, the range of the wavelength from 670 nanometers to 780 nanometers is defined as a blocking zone of the wavelength.Fig. 19 shows a spectral radiation density distribution of the background illuminated by the first light source. The horizontal axis in Fig. 19 indicates the wavelength, and the vertical axis in Fig. 19 indicates the spectral radiation density. The spectral radiation density distribution shown in Fig. 19 is not used in the present example and is shown for reference purposes.The value of the representative wavelength, the value of the comparative wavelength, and the stop band of the wavelength are shown in Figs. 18 and 19.FIG. 20 shows an image of the object to be observed and the background illuminated by the first light source. In this case, the object to be observed is leaves and the background is the ground.FIG. 21 shows an image of the object to be observed and the background illuminated by the second light source emitting the light of the representative wavelength and the comparative wavelength in the additional example of the first aspect of the present invention. Comparing the image of Fig. 21 with the image of Fig. 20, it is understood that the contrast between the object to be observed and the background in Fig. 21 is higher than that in Fig. 20.A method of illumination according to the second aspect of the present invention will be described below.FIG. 22 is a flowchart for describing the method of illumination according to the second aspect of the present invention.In step S 4010 of FIG. 22, the object to be observed and the background are illuminated by the first light source.In step S 4020 of FIG. 22, a spectral radiation density distribution of the object to be observed and that of the background are obtained.In step S 4030 of FIG. 22, a blocking zone of the wavelength is determined in consideration of the spectral radiation density distribution of the object to be observed and the background. For example, the cut-off zone of the wavelength may be set to a range in which the spectral radiation density distribution of the object to be observed and that of the background have a shape similar to each other.In step S 4040 of FIG. 22, the value or values of the representative wavelength are obtained using the spectral radiation density distribution of the object to be observed.In step S 4050 of FIG. 22, the value or values of the comparative wavelength are obtained using the spectral radiation density distribution of the background.In step S 4060 of FIG. 22, the object to be observed and the background are illuminated by the second light source that emits the representative wavelength and the comparison wavelength.A first example of the illumination method according to the second aspect of the present invention will be described.FIG. 23 shows a spectral radiation density distribution of an object to be observed illuminated by the first light source. The horizontal axis of Fig. 23 indicates the wavelength, and the vertical axis of Fig. 23 indicates the spectral radiation density.FIG. 24 shows a spectral radiation density distribution of the background illuminated by the first light source. The horizontal axis of Fig. 24 indicates the wavelength, and the vertical axis of Fig. 24 indicates the spectral radiation density.In accordance with step S 4030 of FIG. 22, a blocking zone of the wavelength is determined in consideration of the spectral radiation density distribution of the object to be observed and that of the background. In this example, the range of the wavelength from 670 nanometers to 780 nanometers is defined as the blocking zone of the wavelength.In accordance with step S 4040 of FIG. 22, the value of the representative wavelength is obtained using the spectral radiation density distribution of the object to be observed. As the value of the representative wavelength, the value of 550 nanometers at which the maximum value of the spectral radiation density distribution of the object to be observed is found for wavelengths outside the cut-off zone of the wavelength was selected. In general, a part or an entire set of the wavelength values at which maximum values of the spectral radiation density distribution of the object to be observed are found may be selected as a value or values of the representative wavelength. Alternatively, an average of the portion or the entire set of wavelength values may be selected.In accordance with step S 4050 of FIG. 22, the value of the comparison wavelength is obtained using the spectral radiation density distribution of the background. As the value of the comparative wavelength, the value of 660 nanometers was selected at which the maximum value of the spectral irradiance distribution of the background is found for wavelengths outside the band-stop of the wavelength. In general, a part or an entire set of the wavelength values at which maximum values of the spectral radiation density distribution of the background are found may be selected as a value or values of the comparative wavelength. Alternatively, an average of the portion or the entire set of wavelength values may be selected.The value of the representative wavelength, the value of the comparative wavelength, and the stop band of the wavelength are shown in Figs. 23 and 24.FIG. 25 shows an image of the object to be observed and the background illuminated by the second light source that emits light of the representative wavelength and light of the comparative wavelength in the first example of the second aspect of the present invention. Comparing the image of FIG. 25 with the image of FIG. 20 obtained with illumination by the first light source, it is understood that the contrast between the object to be observed and the background in FIG. 25 is higher than that in FIG. 20.A second example of the illumination method according to the second aspect of the present invention will be described.FIG. 26 shows a spectral radiation density distribution of an object to be observed illuminated by the first light source. The horizontal axis of Fig. 26 indicates the wavelength, and the vertical axis of Fig. 26 indicates the spectral radiation density.Fig. 27 shows a spectral radiation density distribution of the background illuminated by the first light source. The horizontal axis of Fig. 27 indicates the wavelength, and the vertical axis of Fig. 27 indicates the spectral radiation density.In accordance with step S 4030 of FIG. 22, a blocking zone of the wavelength is determined / determined in consideration of the spectral radiation density distribution of the object to be observed and that of the background. In this example, the range of the wavelength from 670 nanometers to 780 nanometers is defined as the blocking zone of the wavelength.In accordance with step S 4040 of FIG. 22, the value of the representative wavelength is obtained using the spectral radiation density distribution of the object to be observed. As the value of the representative wavelength, the value of 550 nanometers at which the maximum value of the spectral radiation density distribution of the object to be observed is found for wavelengths outside the cut-off zone of the wavelength was selected. In general, a part or an entire set of the wavelength values at which maximum values of the spectral radiation density distribution of the object to be observed are found may be selected as a value or values of the representative wavelength. Alternatively, an average of the portion or the entire set of wavelength values may be selected.In accordance with step S4050 of Fig. 22, the value of the comparison wavelength is obtained using the spectral radiation density distribution of the background. As the value of the comparative wavelength, the value of 430 nanometers was selected at which the minimum value of spectral irradiance distribution is found for wavelengths outside the cut-off zone of the wavelength. In general, a part or an entire set of the wavelength values at which minimum values of the spectral radiation density distribution of the background are found may be selected as a value or values of the comparative wavelength. Alternatively, an average of the portion or the entire set of wavelength values may be selected.The value of the representative wavelength, the value of the comparative wavelength, and the stop band of the wavelength are shown in Figs. 26 and 27.FIG. 28 shows an image of the object to be observed and the background illuminated by the second light source emitting light of the representative wavelength and light of the comparative wavelength in the second example of the second aspect of the present invention. Comparing the image of Fig. 28 with the image of Fig. 20, it is understood that the colors of the sheets to be observed are emphasized against the ground alone in the background.A third example of the illumination method according to the second aspect of the present invention will be described.FIG. 29 shows a spectral radiation density distribution of an object to be observed illuminated by the first light source. The horizontal axis of Fig. 29 indicates the wavelength, and the vertical axis of Fig. 29 indicates the spectral radiation density.FIG. 30 shows a spectral radiation density distribution of the background illuminated by the first light source. The horizontal axis of Fig. 30 indicates the wavelength, and the vertical axis of Fig. 30 indicates the spectral radiation density.In accordance with step S 4030 of FIG. 22, a blocking zone of the wavelength is determined in consideration of the spectral radiation density distribution of the object to be observed and that of the background. In this example, the range of the wavelength from 670 nanometers to 780 nanometers is defined as the blocking zone of the wavelength.In accordance with step S 4040 of FIG. 22, the value of the representative wavelength is obtained using the spectral radiation density distribution of the object to be observed. As the value of the representative wavelength, the value of 430 nanometers at which the minimum value of the spectral radiation density distribution of the object to be observed is found for wavelengths outside the cut-off zone of the wavelength was selected. In general, a part or an entire set of the wavelength values at which minimum values of the spectral radiation density distribution of the object to be observed are found may be selected as a value or values of the representative wavelength. Alternatively, an average of the portion or the entire set of wavelength values may be selected.In accordance with step S 4050 of FIG. 22, the value of the comparison wavelength is obtained using the spectral radiation density distribution of the background. As the value of the comparative wavelength, the value of 660 nanometers at which the maximum value of the spectral irradiance distribution is found for wavelengths outside the cut-off zone of the wavelength was selected. In general, a part or an entire set of the wavelength values at which maximum values of the spectral radiation density distribution of the background are found may be selected as a value or values of the comparative wavelength. Alternatively, an average of the portion or the entire set of wavelength values may be selected.The value of the representative wavelength, the value of the comparative wavelength, and the cut-off zone of the wavelength are shown in Figs. 29 and 30.FIG. 31 shows an image of the object to be observed and the background illuminated by the second light source that emits light of the representative wavelength and light of the comparative wavelength in the third example of the second aspect of the present invention. Comparing the image of Fig. 31 with the image of Fig. 20, it is understood that the colors of the ground in the background are emphasized against the sheets to be observed alone.In the third example, the soil is treated in the same manner as the leaves in the second example in which the leaves are "the object to be observed", and leaves are treated in the same manner as the soil in the second example in which the soil is "the background". Accordingly, the method of the third example is identical to the method of the second example when, in the third example, the ground is regarded as the "object to be observed" and the sheets are regarded as the "background".A method of illumination can be selected from those of the above-described embodiments according to the characteristics of the radiation density distributions of an object to be observed, those of the background and purposes of observation. The most desirable method of illumination may be determined after performing multiple methods of illumination from the embodiments.

Claims

A method for illuminating an object to be observed (200) and the background, the method comprising the steps of: obtaining a color matching function; and obtaining an xy chromaticity diagram using the color matching function; obtaining a relationship between wavelength and spectral irradiance of the object to be observed (200) while the object to be observed (200) and the background are illuminated by a first light source emitting light having an average color rendering index of 40 or more, a color temperature in the range of 3000 K to 10000 K, and a continuous spectrum in the wavelength range of 380 nanometers and 780 nanometers; and obtaining a representative wavelength value corresponding to a local maximum value of the spectral irradiance of the object to be observed (200) plotted against the wavelength; selecting the wavelength, which is closest to the complementary wavelength of the single representative wavelength value in the xy chromaticity diagram as a comparative wavelength value, and illuminates the object to be observed (200) and the background with the light of the representative wavelength value and light of the comparative wavelength value.A method for illuminating an object to be observed (200) and the background, the method comprising the steps of: obtaining a color matching function; and obtaining an xy chromaticity diagram using the color matching function; obtaining a relationship between wavelength and spectral irradiance of the object to be observed (200) while the object to be observed (200) and the background are illuminated by a first light source emitting light having an average color rendering index of 40 or more, a color temperature in the range of 3000 K to 10000 K, and a continuous spectrum in the wavelength range of 380 nanometers and 780 nanometers; and obtaining representative wavelength values corresponding to local maximum values of the spectral irradiance of the object to be observed (200) plotted against the wavelength; selecting the wavelength, corresponding to the point in the xy chromaticity diagram at which a sum of distances from the plurality of points representing the plurality of representative wavelength values in the xy chromaticity diagram is maximized as a comparative wavelength value, and illuminating the object to be observed ( 200) and the background with the light of the representative wavelength values and light of the comparative wavelength value.A method for illuminating an object to be observed (200) and the background, the method comprising the steps of: obtaining a color matching function; and obtaining an xy chromaticity diagram using the color matching function; obtaining a relationship between wavelength and spectral irradiance of the object to be observed (200) while the object to be observed (200) and the background are illuminated by a first light source emitting light having an average color rendering index of 40 or more, a color temperature in the range of 3000 K to 10000 K, and a continuous spectrum in the wavelength range of 380 nanometers and 780 nanometers; and obtaining representative wavelength values corresponding to local maximum values of the spectral irradiance of the object to be observed (200) plotted against the wavelength; selecting the wavelength, which is closest to the complementary wavelength of the average value of the plurality of representative wavelength values in the xy chromaticity diagram as a comparative wavelength value, and illuminates the object to be observed (200) and the background with the light of the representative wavelength values and light of the comparative wavelength value.The illumination method according to any one of claims 1 to 3, wherein a stop zone of the comparison wavelength value is determined before the comparison wavelength value is obtained, and the comparison wavelength value is determined such that the value is outside the stop zone.A method for illuminating an object to be observed (200) and the background, the method comprising the steps of: acquiring a relationship between wavelength and spectral irradiance of the object to be observed (200) while the object to be observed (200) and the background are illuminated by a first light source that emits light having an average color rendering index of 40 or more, a color temperature in the range of 3000 K to 10000 K, and a continuous spectrum in the wavelength range of 380 nanometers and 780 nanometers, and obtaining a representative wavelength value corresponding to a local maximum value of the spectral irradiance of the object to be observed (200) plotted against the wavelength or representative wavelength values corresponding to local maximum values of the spectral irradiance of the object to be observed (200), The wavelength is plotted against the wavelength, acquiring a relationship between wavelength and spectral irradiance of the background while the object to be observed (200) and the background are illuminated by the first light source, and acquiring a comparison wavelength value corresponding to a local maximum value or a local minimum value of the spectral irradiance of the background plotted against the wavelength or comparison wavelength values corresponding to local maximum values or local minimum values of the spectral irradiance of the background plotted against the wavelength, and illuminating the object to be observed (200) and the background with the light of the representative wavelength value or the representative wavelength values and light of the comparison wavelength value or the comparison wavelength values.The illumination method according to claim 5, wherein a blocking zone of the representative wavelength value or values and the comparison wavelength value or values is obtained before the representative wavelength value or values and the comparison wavelength value or values are obtained, and the representative wavelength value or values and the comparison wavelength value or values are obtained such that the representative wavelength value or values and the comparison wavelength value or values are outside the blocking zone.An illumination system (100), the illumination system (100) comprising: a first light source emitting light having an average color rendering index of 40 or more, a color temperature in the range of 3000 K to 10000 K, and a continuous spectrum in the wavelength range of 380 nanometers and 780 nanometers, a spectral irradiance meter (120), a processor (130) connected to the spectral irradiance meter (120), and a second light source for illumination, wherein the system (100) is configured such that a representative wavelength value or values and a comparative wavelength value or values are determined according to the method of claim 1 or the method of claim 5, for illumination with the second light source.The lighting system (100) of claim 7, wherein the second light source is comprised of the first light source and a plurality of filters.

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