JP5354098B2 - Illumination optical system, reflection characteristic measuring apparatus, and illumination method - Google Patents

Abstract

Disclosed is an illumination optical system which makes it possible to decrease the rate of the change in the illumination that depends on the variation in the distance between the illumination optical system and the light source, even if a light source having a non-Lambertian light distribution property is employed. A light source (2) is located such that the distance (D1) between the light source (2) and a normal line (1n) is equal to the distance (D2) between the light source (2) and a sample surface (1) and that a light distribution main axis (2x) of the light source (2) is inclined at a predetermined offset angle (d) with respect to a normal line (2n) which is normal to the sample surface (1) and passes through the light source (2). The offset angle (d) is set such that the rate of the change in illumination with a non-Lambertian light distribution at an angle of (45°-d) with respect to the light distribution main axis (2x) is equal to that in illumination with the Lambertian light distribution at an angle of 45° with respect to a light distribution main axis thereof.

Description

  The present invention relates to a reflection characteristic measuring apparatus for measuring reflection characteristics of a plurality of color samples, an illumination method using the reflection characteristic measuring apparatus, and an illumination optical system used for the reflection characteristic measuring apparatus.

  In the calibration of the printing color of a color printer or the like, the spectral reflection characteristics in the visible wavelength band (400 to 700 nm) of a large number (for example, several hundreds) of color samples having different color tones and densities printed on paper are measured, and the measured values and This is performed based on a deviation from the reference value of each color sample. Spectral reflection characteristics of color samples are measured by setting the normal angle (angle from the normal of the sample surface) to 45 °, illuminating the sample surface from all directions or from many directions, and reflecting in the normal direction. So-called 45 ° a: 0 ° geometry (a: annular) and 45 ° c: 0 ° geometry (c: circumferential) are recommended. This measuring method has a feature that the influence of the inclination and anisotropy of the sample surface can be suppressed.

  When a large number of color samples are measured with a reflection characteristic measuring apparatus for ordinary spot measurement, it takes time and labor. For this reason, an automatic scanning type reflection characteristic measuring apparatus that can sequentially acquire the spectral reflection characteristics of each color sample by scanning 20 to 40 color samples arranged one-dimensionally is generally adopted. Is.

  In addition, some automatic scanning type reflection characteristic measuring apparatuses are built in a color printer. An automatic scanning type reflection characteristic measuring apparatus built in a color printer conveys a printed matter in which color samples are arranged two-dimensionally to a color printer, and scans one row of color samples one-dimensionally to produce one row of color samples. The spectral reflection characteristics of a number of color samples are acquired by repeating the measurement of the spectral reflection characteristics.

  In the case of a reflection characteristic measuring device built in a color printer, a change in the distance between the illumination optical system and the sample surface is unavoidable with conveyance and scanning. If the distance between the illumination optical system and the sample surface varies, the illuminance on the sample surface becomes unstable, resulting in measurement errors. For this reason, in the reflection characteristic measuring apparatus, it is required to suppress a change in illuminance accompanying a variation in the distance between the illumination optical system and the sample surface.

  Therefore, the reflection characteristic measuring apparatuses shown in Patent Document 1 and Patent Document 2 are known. FIG. 12 is a configuration diagram of the reflection characteristic measuring apparatus shown in Patent Document 1 and Patent Document 2. The reflection characteristic measuring apparatus shown in FIG. 12 includes a Lambert light distribution light source 2. The light source 2 is arranged in parallel with the normal 1n of the sample surface 1 with the light distribution main axis 2x passing through the center O of the sample surface 1. The light source 2 is arranged such that the distance D1 to the normal line 1n and the distance D2 to the sample surface 1 are equal to D.

  As a result, the center O of the sample surface 1 is illuminated by the luminous flux component 2a of the radiated light from the light source 2 with the opposite main axis angle (angle from the light distribution main axis 2x) θ being θ = 45 °. The luminous flux component 1a in the normal direction of the reflected light enters the spectroscopic unit 6 through the light receiving optical system 5, and the spectral reflection characteristics are measured.

Here, the distance D2 (= D) between the light source 2 and the sample surface 1 is changed to D + d, the distance L between the light source 2 and the center O of the sample surface 1 is changed to L ′, and the angle θ is changed. Suppose that it has changed. The distance L is represented by D / sin (θ). The illuminance I is inversely proportional to the square of the distance L. Therefore, the illuminance I is proportional to sin ² (θ).

On the other hand, the light flux density emitted from the light source 2 at the angle θ is proportional to cos (θ). The density of the light beam incident on the sample surface 1 at an incident angle (angle from the normal 1n) θ is also proportional to cos (θ). Therefore, the illuminance I (θ) on the sample surface 1 of the light beam component 2a is proportional to sin ² (θ) · cos ² (θ). Eventually, the illuminance I (θ) is proportional to sin ² (2θ). Therefore, when K is a proportionality constant, it is expressed by Expression (1).

I (θ) = K · sin ² (θ) · cos ² (θ) = K · sin ² (2θ) (1)

Since sin ² (2θ) becomes maximum when θ = 45 ° and the differential coefficient becomes 0, the change rate of the illuminance I (θ) of the sample surface 1 with respect to the change of θ, that is, the change of the distance D is θ = 45. Minimized around °.

  FIG. 13 is a graph showing the change in illuminance with respect to the displacement d of the distance D in each of the Lambert light distribution, the light distribution P_450 in the 450 nm wavelength band of the actual white LED, and the light distribution P_600 in the 600 nm wavelength band. is there.

  In FIG. 13, the distance D is D = 20 mm, and the displacement d is in the range of d = −0.35 mm to +0.35 mm. In FIG. 13, the vertical axis indicates the change in illuminance, and the ratio of the illuminance I (θ ′) when D2 = D + d to the illuminance I (θ) when D2 = D. The horizontal axis indicates the displacement d. Further, the graph represented by ◇ shows the case of Lambert light distribution, the graph represented by □ shows the case of light distribution P_600, and the graph represented by Δ shows the case of light distribution P_450.

  In the case of Lambert light distribution, it can be seen that the change in illuminance is suppressed to 0.01% with respect to the fluctuation of d = 0.2 mm.

  However, in Patent Document 1 and Patent Document 2, it is assumed that the light source 2 emits light of Lambert light distribution (cosine light distribution). Therefore, when the light source 2 having a non-Lambertian light distribution other than the Lambertian light distribution is employed, there arises a problem that the illuminance greatly changes with respect to the displacement d. In particular, as the light distribution is biased toward the light distribution main axis 2x, the change in illuminance with respect to the displacement d becomes more significant.

  FIG. 14 is a graph showing a light distribution P_450 and a light distribution P_600 when a white LED including a blue LED and a fluorescent material excited by the emitted light of the blue LED is employed as the light source 2. In FIG. 14, the graph represented by Δ represents the light distribution P_450, and the graph represented by □ represents the light distribution P_600. In FIG. 14, the straight line drawn radially indicates the angle, and the radial direction indicates the relative intensity of the light.

  As shown in FIG. 14, the light distribution P_600 is almost a perfect circle and is close to the Lambert light distribution. On the other hand, the light distribution P_450 is biased in the direction of the light distribution main axis (the direction of 0 °) rather than the Lambert light distribution.

  Therefore, as shown by Δ in FIG. 13, it can be seen that the illuminance of the light distribution P_450 is changed by about 1% with respect to the distance variation of d = 0.2 mm. Therefore, when the above white LED is employed as the light source 2 in the reflection characteristic measuring apparatuses of Patent Documents 1 and 2, an illuminance change of about 1% occurs in a short wavelength band with a distance variation of d = 0.2 mm, thereby There is a problem that an error also occurs in the reflection characteristic measurement value.

US Pat. No. 7,365,843 USP7433301 JP 2008-298579 A

  An object of the present invention is to provide a technique for suppressing a change in illuminance accompanying a variation in the distance between an illumination optical system and a sample surface even when a non-Lambertian light source is employed.

An illumination optical system according to an aspect of the present invention includes a light source that emits surface light with non-Lambertian light distribution, and illuminates the sample surface at an angle of 45 ° from a normal line of the sample surface that passes through the center of the sample surface to be measured. In the illumination optical system, the light source has a substantially equal distance from a center of the light emitting surface of the light source to a normal line of the sample surface and a distance from the center of the light emitting surface to a plane including the sample surface. And a light distribution main axis perpendicular to the light emitting surface of the light source is arranged to be inclined by a predetermined offset angle with respect to the normal line of the sample surface, and the offset angle is a normal line of the sample surface to the sample surface. And an angle that suppresses a change in illuminance on the sample surface when it fluctuates in the direction.

  A reflection characteristic device according to another aspect of the present invention receives reflected light from the normal direction of the sample surface when the illumination optical system and the light source of the illumination optical system illuminate the sample surface. And a spectroscopic unit that measures the reflection characteristics of the sample surface based on the reflected light received by the light receiving optical system.

An illumination method according to yet another aspect of the present invention illuminates the sample surface at an angle of 45 ° from the direction of the normal of the sample surface passing through the center of the sample surface to be measured, and the reflected light on the sample surface Is an illumination method for measuring the reflection characteristics of the sample surface from a direction normal to the sample surface , wherein a light source that emits surface light by non-Lambertian light distribution from the center of the light emitting surface of the light source A first step in which the distance to the normal line of the sample surface and the distance from the center of the light emitting surface to a plane including the sample surface are substantially equal; and a light distribution perpendicular to the light emitting surface of the light source A second step of disposing the main axis at a predetermined offset angle (δ) with respect to the normal of the sample surface, wherein the offset angle varies in the direction of the normal of the sample surface. And an angle to suppress a change in illuminance on the sample surface.

It is a block diagram of the reflection characteristic measuring apparatus by Embodiment 1 of this invention. It is the graph which showed the change of the illumination intensity with respect to the displacement of a sample surface in each of Lambert light distribution and 450 nm wavelength band light distribution. It is the graph which showed the illumination intensity change rate with respect to an offset angle in each of the light distribution of a 450 nm wavelength band, and the light distribution of a 600 nm wavelength band. 6 is a configuration diagram of a white LED employed as a light source of Embodiment 2. FIG. It is the graph which showed the change of the illumination intensity with respect to the displacement of the sample surface of light distribution P_450 and light distribution P_600 at the time of setting the optimal offset angle of light distribution P_450 as an offset angle of a light source. It is a spectral distribution when the white LED shown in FIG. 4 is used as a light source. It is a block diagram of the reflection characteristic measuring apparatus by Embodiment 3 of this invention. It is a block diagram of the reflection characteristic measuring apparatus by Embodiment 4 of this invention. It is a figure for demonstrating the magnitude | size of the plane mirror in Embodiment 4 of this invention. (A) shows the block diagram of the reflection characteristic measuring apparatus in Embodiment 5 of this invention, (B) is the block diagram of the light source in Embodiment 5. FIG. 7 is a spectral distribution of a light source according to a fifth embodiment. It is a block diagram of the reflection characteristic measuring apparatus shown in patent document 1 and patent document 2. It is the graph which showed the change of the illumination intensity with respect to the displacement of the distance D in each of Lambert light distribution, light distribution of a 450 nm wavelength band, and light distribution of a 600 nm wavelength band. It is a graph which shows 450 nm wavelength band light distribution and 600 nm wavelength band light distribution measured about white LED containing blue LED as a light source and the fluorescent material excited by the emitted light of blue LED.

(Embodiment 1)
FIG. 1 is a configuration diagram of a reflection characteristic measuring apparatus according to Embodiment 1 of the present invention. In addition, in Embodiment 1-5 shown below, description is abbreviate | omitted about the same thing. As shown in FIG. 1, the reflection characteristic measuring apparatus includes a sample surface 1, a light source 2, a light receiving optical system 5, and a spectroscopic unit 6. In the present embodiment, the light source 2 constitutes an illumination optical system. This illumination optical system is an illumination optical system that illuminates the sample surface 1 at an angle of 45 ° from the normal 1n of the sample surface 1 passing through the center O of the sample surface 1.

  The light source 2 is a light source that emits light by non-Lambertian light distribution having a light distribution 2d that is biased toward a light distribution main axis 2x perpendicular to the light emitting surface. In the light source 2, the distance D1 to the normal line 1n and the distance D2 to the sample surface 1 are substantially equal, and D1 = D2 = D. In the incident surface, the light source 2 is installed such that the light distribution main axis 2x is inclined by a predetermined offset angle δ with respect to the normal 2n. The light source 2 illuminates the sample surface 1 with a light flux component 2a having an angle from the normal 1n (normal angle) of 45 °. The incident surface is a surface including the normal 1n and the center of the light emission region of the light source 2, and corresponds to the paper surface in FIG. The normal line 2n is a normal line of the sample surface 1 passing through the center of the light emission region of the light source 2.

  The normal component 1a of the reflected light from the illuminated sample surface 1 is incident on the spectroscopic unit 6 through the light receiving optical system 5, and a 45 °: 0 ° geometry is realized. The spectroscopic unit 6 measures the spectral characteristics of the incident light and outputs it to an arithmetic processing unit (not shown). The arithmetic processing unit obtains the spectral reflectance coefficient and the color value of the sample surface 1 for the spectral characteristics measured by the spectroscopic unit 6 using a known method.

  Here, the angle θ formed by the luminous flux component 2a and the normal 2n is equal to 45 °. However, since the light distribution main axis 2x is inclined from the normal 2n by the offset angle δ, the main axis angle φ of the luminous flux component 2a is φ = Θ−δ = 45 ° −δ. The main axis angle φ is an angle of the light beam component 2a with respect to the light distribution main axis 2x.

  When the light distribution 2d is represented by P (φ), the offset angle δ is the Lambert distribution of the change rate dP / dφ (= dP / dθ) of the light distribution P (φ) at the main shaft angle φ = 45 ° −δ. It is set to be equal to the rate of change dPL / dθ = −sin (θ) when the angle of the main axis of the light PL (θ) = cos (θ) is 45 °. That is, the offset angle δ is set so as to satisfy Expression (2).

dP / dθ _{φ = 45 ° −δ} = dPL / dθ _{θ = 45 °} = −sin (θ) _{θ = 45 °} (2)

  Therefore, as shown in Equation (3), P (φ) in the vicinity of φ = 45 ° −δ (represented by φ≈45 ° −δ) is in the vicinity of θ = 45 ° (represented by θ≈45 °). It is possible to be proportional to PL (θ) = cos (θ).

P (φ) φ≈45 _{° −δ} ∝cos (θ) θ≈45 _° (3)

Here, it is assumed that the distance D2 changes to D + d, the distance L between the light source 2 and the center O of the sample surface 1 changes to L ′, and the angle θ changes to θ ′. Since the distance L is L = D / sin (θ) and the light flux density is inversely proportional to the square of the distance L, the light flux density A1 incident on the sample surface 1 at the incident angle θ is proportional to sin ² (θ) ( A1 = a1 · sin ² (θ)). The light flux density A2 incident on the sample surface 1 at an incident angle θ is proportional to cos (θ) (A2 = a2 · cos (θ)).

As described above, the light flux density A3 emitted from the light source 2 with respect to the main axis angle φ is proportional to cos (θ) in the vicinity of φ = 45 ° −δ, that is, in the vicinity of θ = 45 ° (A3 = a3 · cos θ). Therefore, the illuminance I (θ) of the sample surface 1 due to the luminous flux component 2a is proportional to A1, A2, and A3 in the vicinity of θ = 45 ° and is expressed by K · sin ² (θ) · cos ² (θ). .

  Therefore, the illuminance I on the sample surface 1 due to the luminous flux component 2a when the distance D2 changes to D + d, the distance L between the light source 2 and the center O of the sample surface 1 changes to L ′, and the angle θ changes to θ ′. (Θ) is approximately expressed by equation (1).

Therefore, if δ is set so that dP / dθ _{φ = 45 ° −δ} = dPL / dθθ _{= 45 °} , the sample surface 1 with respect to the change of the distance D2 for the same reason as the methods of Patent Documents 1 and 2. The change rate of the illuminance I (θ) can be minimized in the vicinity of θ = 45 °.

  FIG. 2 is a graph showing a change in illuminance with respect to the displacement d in each of the Lambert light distribution after the offset angle δ is set and the light distribution P_450 in the wavelength band of 450 nm. In FIG. 2, the distance D is D = 20 mm, and the displacement d is d = −0.35 mm to +0.35 mm.

  In FIG. 2, the vertical axis indicates the change in illuminance, and the ratio of the illuminance I (θ ′) when D2 = D + d to the illuminance I (θ) when D2 = D. The horizontal axis represents the displacement d of the sample surface 1. Further, the graph represented by ◇ shows the case of Lambert light distribution, and the graph represented by Δ shows the case of light distribution P_450.

  As shown in FIG. 2, in the light distribution P_450, the change in illuminance is substantially flat with respect to d, and it can be seen that the change in illuminance is suppressed to a level comparable to that of Lambert light distribution.

  Hereinafter, a specific method for setting the offset angle δ will be described. The main axis angle φ of the luminous flux component 2a is φ = θ−δ because the light distribution main axis 2x of the light distribution 2d is inclined from the normal 2n by the offset angle δ. When the light distribution 2d is represented by P (φ), the light beam density of the light beam component with respect to the main axis angle φ is P (φ) = P (θ−δ). Therefore, the illuminance I (θ, δ) of the sample surface 1 illuminated with the luminous flux component 2a replaces one of cos (θ) on the right side of the equation (1) with P (φ) = P (θ−δ). It is expressed by the following formula (4).

I (θ, δ) = K · sin ² (θ) · cos (θ) · P (θ−δ) (4)

When the offset angle δ is set to a certain value, the illuminance I (45 °, δ) at d = 0, that is, θ = 45 ° is K · sin ² (45 °) · cos (45 °) · P It is represented by (45 ° −δ). When the angle θ when the displacement d of the distance D1 reaches the maximum value (d ′) that can be assumed is θ ′, the illuminance I (θ ′, δ) is K · sin ² (θ ′) · cos (θ ′) · P (θ′−δ).

  Here, the ratio of the illuminance I (θ ′, δ) to the illuminance I (45 °, δ) is defined as the illuminance change rate R (δ). Then, R (δ) is expressed by Equation (5).

R (δ) = I (θ ′, δ) / I (45 °, δ) = (sin ² (θ ′) · cos (θ ′) · P (θ′−δ)) / (sin ² (45 ° ) · Cos (45 °) · P (45 °-δ)) (5)

  As can be seen from equation (5), when R (δ) = 1, there is no change in illuminance. Therefore, it is only necessary to obtain δ such that R (δ) = 1. Specifically, the illuminance change rate R (δ) is obtained by changing δ at a predetermined pitch, and δ that has R (δ) closest to 1 may be set as the offset angle δ.

  Thereby, the offset angle δ is the maximum illuminance at the center O when the displacement in the normal 1n direction of the sample surface 1 can be assumed with respect to the illuminance at the center O of the sample surface 1 at the initial position by the light source 2. It is set to an angle that minimizes the change of.

  FIG. 3 is a graph showing dR (δ) (= R (δ) −1) with respect to the offset angle δ in each of the light distribution P_450 in the 450 nm wavelength band and the light distribution P_600 in the 600 nm wavelength band. In FIG. 3, the distance D is D = 20 mm, and the displacement d is d = 0 to 0.2 mm. When the displacement d is 0 to 0.2 mm, the angle θ varies in the range of 44.7 ° to 45 °. Therefore, the illuminance change rate R (δ) = I (44.7 °, δ) / I (45 °, δ).

  In FIG. 3, the vertical axis represents the change in illuminance change rate R (δ) −1 = dR (δ), and the horizontal axis represents the offset angle δ. In FIG. 3, the graph represented by Δ represents dR (δ) of the light distribution P_450, the graph represented by □ represents dR (δ) of the light distribution P_600, and the graph represented by x represents dR (δ) of the light distribution P_450. ) And the difference ddR (δ) between the light distribution P_600 and dR (δ).

  In the graph of FIG. 3, when dR (δ) = 0, the illuminance change rate R (δ) = 1. Therefore, δ where dR (δ) = 0 is the offset angle. In the example of FIG. 3, the light distribution P_450 is dR (δ) = 0 at δ≈27 °. Therefore, the offset angle δ is δ = 27 °.

  In the measurement of FIG. 3, as the light distributions P_450 and P_600, for example, light distributions P_450 and P_600 may be measured at predetermined intervals (for example, 5 °) and the measured values may be interpolated. Alternatively, the approximate function of the light distribution P (φ) may be P (φ) = cos (k · φ), k may be obtained by parameter fitting, and the obtained light distribution P (φ) may be used. In this case, the light distributions P_450 and P_600 are measured at predetermined intervals (for example, 5 °), and the obtained measured values are best fit in a range of 0 ° to 45 ° using, for example, the least square method. What is necessary is just to obtain the constant k.

  When the displacement occurs evenly in the positive and negative directions, the offset angle δ obtained from the equation (5) is generally larger than the offset angle δ obtained from the equation (2). In particular, when the light distribution P (φ) is greatly deviated from the Lambert light distribution, the difference between the offset angle δ obtained from Equation (5) and the offset angle δ obtained from Equation (2) becomes large. As shown in FIG. 13, the illuminance change rate R (δ) increases as the assumed displacement d increases, and the difference between the illuminance change rate R (δ) between the light distribution P (φ) and the Lambert light distribution also increases. .

  When the offset angle δ set for the light source 2 is larger than the optimum offset angle δ_op, the versus main shaft angle φ (= 45 ° −δ) is smaller than the opposite main shaft angle φ_op when the optimum offset angle δ_op is set. And it is preferable that the counter-spindle angle φ is smaller than the counter-spindle angle φ_op. Therefore, the method of equation (5) has a larger offset angle δ than the method of equation (2), and thus a more preferable offset angle δ can be obtained.

(Embodiment 2)
The reflection characteristic measurement apparatus according to the second embodiment is characterized in that a high-efficiency and long-life white LED is used as the light source 2 in the reflection characteristic measurement apparatus of FIG. In the present embodiment, as a white LED, a white LED including a blue LED that emits radiated light in the vicinity of 450 nm and a fluorescent material that is excited by the radiated light of the blue LED and emits fluorescence in a wavelength band centered on 600 nm. adopt. This white LED is characterized by high efficiency and low cost.

  FIG. 4 is a configuration diagram of a white LED employed as the light source 2 of the present embodiment. The white LED shown in FIG. 4 includes an LED chip 2c, a resin 2r, and a package 2p. The LED chip 2c is composed of a blue LED that emits radiated light having a half width of about 20 nm centered at 450 nm. The resin 2r is applied to the surface of the chip 2c, and the powdery fluorescent material dispersed in the resin 2r is excited by a part of the emitted light of the LED chip 2c, and has a wavelength band with a half-value width of about 150 nm centered at 600 nm. Emits fluorescence. The package 2p is transparent and emits both the emitted light of the LED chip 2c diffused by the resin 2r and the fluorescence of the resin 2r.

  FIG. 6 shows a spectral intensity distribution when the white LED shown in FIG. 4 is used as the light source 2. In FIG. 6, the vertical axis indicates relative intensity, and the horizontal axis indicates wavelength.

  As shown in FIG. 6, it can be seen that the spectral intensity distribution of the white LED is 430 nm or less and there is almost no intensity. As shown in FIG. 4, the fluorescent light distribution 2f emitted from the resin 2r is a Lambertian light distribution, but the diffused light distribution 2d of the diffused LED chip 2c is more biased toward the light distribution main axis than the Lambertian light distribution. In many cases, it is non-Lambertian light distribution. That is, the white LED has a different light distribution depending on the wavelength band.

  Thus, when one light source 2 has a different light distribution for each wavelength band, the offset angle δ set for the light distribution with the largest deviation to the light distribution main axis 2x may be set as the offset angle δ of the light source 2. . Thereby, the change of the illumination intensity with respect to the change of the distance D2 can be optimally suppressed over the entire wavelength band. In the reflection characteristic measuring apparatus including the light source 2 of FIG. 4, the offset angle δ set for the light distribution 2 d may be set as the offset angle δ of the light source 2. This reason is explained by the following two points.

  (1) As shown in FIG. 3, the change in the illuminance change rate with respect to the offset angle δ is smaller as the light distribution is closer to the Lambert light distribution. Therefore, in the light distribution close to the Lambert light distribution, even if the offset angle δ set for the light source 2 deviates from its own optimum offset angle δ_op, the change in the illuminance change rate is small. On the other hand, in the light distribution greatly deviated from the Lambert light distribution, the change in the illuminance change rate is large when the offset angle δ set for the light source 2 deviates from its own optimum offset angle δ_op.

  (2) When the offset angle δ set for the light source 2 is smaller than the optimum offset angle δ_op1 of a certain light distribution P1 (φ) (δ <δ_op1), the main shaft angle φ ( = 45 ° −δ) increases. In addition, when the offset angle δ set for the light source 2 is larger than the optimum offset angle δ_op1 of the light distribution P1 (φ) (δ> δ_op), the main shaft angle φ of the light distribution P1 (φ) becomes small.

  The change rate dP1 / dφ of the light distribution P1 (φ) tends to increase as the opposite main shaft angle φ increases. Therefore, if the offset angle δ set for the light source 2 is smaller than the optimum offset angle δ_op1 of the light distribution P1 (φ), the opposite main axis angle φ of the light distribution P1 (φ) increases, and therefore the light distribution P1 ( The change rate dP1 / dφ of φ) greatly deviates from the change rate dPL / dθ of Lambert light distribution PL (θ).

  On the other hand, when the offset angle δ set for the light source 2 is larger than the optimum offset angle δ_op1 of the light distribution P1 (φ), the opposite-to-main-axis angle φ becomes small, so the rate of change P1 / dφ of the light distribution P1 (φ). Does not greatly deviate from the change rate dPL / dθ of the Lambert light distribution PL (θ).

  Among the plurality of light distributions, the optimum offset angle δ_opx of the light distribution PX (φ) having the largest deviation to the light distribution main axis is the largest. Therefore, when the offset angle δ of the light source 2 is set to δ_opx, the opposite main axis angle φ of the other light distribution PY (φ) is the opposite main axis when the optimum offset angle δ_opy is set with respect to the light distribution PY (φ). It becomes smaller than the angle φ_y.

  Therefore, it is preferable to set the optimum offset angle δ_opx of the light distribution PX (X) having the greatest deviation to the light distribution main axis among the plurality of light distributions as the offset angle δ of the light source 2.

  FIG. 5 is a graph showing a change in illuminance with respect to the displacement d of the light distribution P_450 and the light distribution P_600 when the optimum offset angle δ_450 of the light distribution P_450 is set as the offset angle δ of the light source 2. In FIG. 5, the vertical axis represents the illuminance change rate R (δ), and the horizontal axis represents the displacement d.

  Compared to the graph of the light distribution P_450 shown in FIG. 13, in FIG. 5, the offset angle δ is set to δ_450, so the graph of the light distribution P_450 is flat and the change rate of the illuminance with respect to the displacement d is small. I understand. Further, in FIG. 5, the graph of the light distribution P_600 is also almost flat, and it can be seen that the change rate of the illuminance with respect to the displacement d is kept low as a whole.

  As described above, by setting the optimum offset angle δ_450 as the offset angle δ of the light source 2 for the light distribution P_450 having a large deviation to the light distribution main axis 2x compared to the light distribution P_600, the displacement d is changed in both light distributions. The change of the illumination intensity with respect to can be suppressed.

  The difference in the change rate of the illuminance with respect to the displacement d between the light distribution P_450 and the light distribution P_600 is a difference between the wavelength bands of the spectral reflectance coefficients. Since this difference is often amplified in the color difference value obtained from the spectral reflectance coefficient, it is significant to reduce the difference ddR of dR (δ) between wavelength bands.

  In the present embodiment, as shown in FIG. 4, since there are two light distributions 2d and 2f, the illuminance change rate R (δ) for each of the light distributions 2d and 2f is the same as in the first embodiment. ) And the optimum offset angle δ_opd of the light distribution 2d having a large deviation to the light distribution main axis may be set as the offset angle δ to be set in the light source 2.

  In the example of FIG. 3, the graph of the light distribution P_450 intersects with the horizontal axis when δ = 27 °, so δ = 27 ° is set. However, as described above, ddR, which is the difference between the light distributions P_450 and P_600, causes a color difference value error. Therefore, when emphasizing the color value error, it is preferable to set an angle larger than 27 ° as the offset angle δ of the light source 2 so that ddR becomes small.

(Embodiment 3)
As shown in FIG. 6, the spectral intensity distribution of the white LED has two peaks in the visible light wavelength band (400-700 nm), and the intensity is low near both ends. In particular, there is almost no intensity in a short wavelength band of 430 nm or less.

  In printing color calibration, the spectral intensity distribution of all visible light wavelength bands is required. Therefore, in the fourth embodiment, a purple LED is used in combination with a white LED in order to cover the intensity of the short wavelength band.

  Further, since the reflection characteristic measuring apparatus of FIG. 1 is illuminated only from one side, the measured value may vary depending on the direction of illumination when the sample surface 1 is tilted or has anisotropy. In order to cope with these, a plurality of light sources 2 are arranged in the third embodiment.

  7 shows a configuration diagram of a reflection characteristic measuring apparatus according to Embodiment 3 of the present invention, (A) shows the arrangement of the light source 2 from a top view, and (B) shows a reflection characteristic measurement apparatus from a side view. The configuration is shown.

  In the present embodiment, six light sources 21 to 21 arranged at intervals of 60 degrees on the circumference of the radius D centering on the normal line 1n in a plane parallel to the sample surface 1 that is separated from the sample surface 1 by a distance D. 26. The light sources 21, 23, and 25 are white LEDs, and the light sources 22, 24, and 26 are made of purple LEDs. That is, in this Embodiment, white LED and purple LED are arrange | positioned alternately.

  Since the white LED and the purple LED have different light distributions, the optimum offset angles δ1 and δ2 are also different. The light sources 21, 23, and 25 are arranged such that the light distribution main axes 21x, 23x, and 25x are inclined by the offset angle δ1 with respect to the normal 1n. The light sources 22, 24, and 26 are arranged such that the light distribution main axes 22x, 24x, and 26x are inclined with respect to the normal line 1n by the offset angle δ2.

  Since the light sources 21, 23, 25 are white LEDs, the offset angle δ set for the above-described light distribution P_450 is set as the offset angle δ1 of the light sources 21, 23, 25.

  Since the light sources 22, 24, and 26 are violet LEDs, the illuminance change rate R (δ2) is obtained by substituting the light distribution of the violet LEDs into the equation (5), and the offset angle δ2 is determined in the same manner as in the first embodiment. Find it.

  According to this reflection characteristic measuring apparatus, it is possible to cover the entire visible light wavelength band (400 to 700 nm) and to suppress the change in illuminance accompanying the displacement d over the entire visible light wave band. Furthermore, since the white LED and the purple LED each illuminate the sample surface 1 from three directions, a 45 ° c: 0 ° geometry (c: circular) is realized that is not easily affected by the inclination of the sample surface 1 or anisotropy. can do.

  In the third embodiment, when a certain light source has a plurality of light distributions, the offset angle δ set for the light distribution with the maximum deviation to the light distribution main axis is set to the light source as in the second embodiment. May be set as the offset angle δ.

(Embodiment 4)
The reflection characteristic measuring apparatus according to Embodiment 4 includes one light source 12, and radiates light from the light source 12 by a plurality of plane mirrors 3 to illuminate the center O of the sample surface 1.

  FIG. 8 is a configuration diagram of a reflection characteristic measuring apparatus according to Embodiment 4 of the present invention, (A) is a configuration diagram from a side view, (B) is an arrangement of a plane mirror 3 from a top view, (C) is a block diagram when paying attention to one plane mirror 3.

  The light source 12 (an example of an actual light source) is a non-Lambertian light source that emits light by surface light emission, and the light distribution main axis 12x of the light distribution 12d that is orthogonal to the light emitting surface is arranged to coincide with the normal line 1n. A plurality of plane mirrors 3 are arranged symmetrically between the sample surface 1 and the light source 12 with the normal 1n as an axis of symmetry.

  Each of the plane mirrors 3 reflects the light beam component 12a of the light source 12 with respect to the principal axis angle φ by the reflection surface 3a and guides it to the center O. Thereby, the center O is illuminated by the light beam component 12a having a normal angle of 45 ° from a plurality of directions.

  In the present embodiment, the light distribution 12d is a non-Lambertian light distribution. Therefore, in the plane mirror 3, the light distribution main axis 12′x of the light source image 12 ′ is inclined by a predetermined offset angle δ with respect to the normal 2n of the sample surface 1 passing through the light source image 12 ′ of the light source 12 by the reflection surface 3a. Are arranged as follows. The light source image 12 ′ is a virtual light source that is axisymmetric to the light source 12 with respect to the reflecting surface 3 a of the plane mirror 3.

  As in the first embodiment, the offset angle δ is such that the change rate of the light distribution of the light source 12 at an angle of 45 ° −δ with respect to the light distribution main axis 12′x is 45 ° with respect to the light distribution main axis of the Lambert light distribution. Is set to an angle that is substantially equal to the rate of change in the angle.

  The offset angle δ may be set by adopting the same method as in the first and second embodiments. The reflecting mirror 4 is disposed at a predetermined position on the normal line 1n and between the light source 12 and the center O, and changes the optical path of the normal component 1a of the reflected light on the sample surface 1 by approximately 90 °. The reflected light is incident on the spectroscopic unit 6 through the light receiving optical system 5, the spectral characteristics are measured, and output to an arithmetic processing unit (not shown). The arithmetic processing unit obtains the spectral reflectance coefficient and the color value of the sample surface 1 from the spectral characteristics measured by the spectroscopic unit 6 using a known method. As a result, an illumination optical system having a 45 ° c: 0 ° geometry (c: circular) is realized.

  As shown in FIG. 8C, in the plane mirror 3, the reflecting surface 3a is perpendicular to the incident surface including the light source image 12 'and the normal 1n, and the normal of the sample surface 1 passing through the center O3 of the reflecting surface 3a. It is arranged to be inclined by δ / 2 with respect to 3n.

  Assuming that the distance between the sample surface 1 and the light source 12 is D3, the distance d3 from the center O3 of the reflecting surface 3a to the normal line 1n is equal to the distance d3 from the center O3 of the reflecting surface 3a to the sample surface 1, and d3 = D3 / (Cot (45 ° −δ) +1).

  As is clear from FIG. 8C, the light source image 12 ′ is on the optical axis 12′a having an incident angle of 45 ° with respect to the sample surface 1, and the distance from the normal 1n and the distance from the sample surface 1 are It is arranged at a position where both distances are d4.

  In FIG. 8, there are 16 plane mirrors 3. Therefore, although the sample surface 1 is illuminated with 16 light source images 12 ′, the light distribution main axis 12′x of each light source image 12 ′ is arranged to be inclined by the offset angle δ. Even if it occurs, the change in illuminance is suppressed.

  In the present embodiment, since the 45 ° c: 0 ° geometry is realized using one light source 12, the use of light flux is used compared to the case where a 45 ° c: 0 ° geometry is realized using a plurality of light sources. High efficiency, low power consumption, low heat generation, and low cost can be obtained. In the present embodiment, when a white LED is used as the light source 12 and white calibration shown in Japanese Patent Laid-Open No. 2008-298579 is performed, the forward voltage of only one light source is monitored because there is only one light source 12. The configuration can be simplified.

  Although the utilization efficiency of the light beam increases as the number of the plane mirrors 3 increases, the present embodiment assumes that the illuminance is inversely proportional to the square of the distance between the light source 12 and the sample surface 1. Therefore, the plane mirror 3 needs to have a size that reflects the total luminous flux from the light source 12 toward the measurement region 1 f of the sample surface 1.

  FIG. 9 is a diagram for explaining the size of the plane mirror 3 in the present embodiment. In FIG. 9, the plane mirror 3 from the top view is shown. As shown in FIG. 9, the plane mirror 3 is set to be larger than the irradiation area on the reflection surface 3a of the total luminous flux from the light source image 12 ′ of the reflection surface 3a toward the measurement region 1f of the sample surface 1. That is, the width W in the top view of the plane mirror 3 is the width l1 of two points where two light beams connecting the region 12′_D and the outermost contour of the measurement region 1f in the top view of the light source image 12 ′ intersect the reflecting surface 3a. It is set to a larger value. Similarly to the width W in the top view, the width of the plane mirror 3 in the side view is set to a value larger than the width of the intersection of the two outermost rays in the side view and the reflecting surface 3a. Therefore, in the present embodiment, the number of plane mirrors 3 is limited to a number that prevents the width W from becoming smaller than the width l1.

(Embodiment 5)
The reflection characteristic measurement apparatus according to the fifth embodiment is the reflection characteristic measurement apparatus according to the fourth embodiment, in which the light source 12 includes a blue LED and a fluorescent material that is excited by the emitted light of the blue LED and emits fluorescence. And a purple LED.

  FIG. 10A shows a configuration diagram of the reflection characteristic measuring apparatus in the fifth embodiment, and FIG. 10B shows a configuration diagram of the light source 12 in the fifth embodiment.

  As shown in FIG. 6, since the spectral intensity distribution of the white LED is 430 nm or less and there is almost no intensity, it is not possible to obtain the reflection characteristics of the visible light in the entire wavelength band (400 to 700 nm). Therefore, the configuration shown in FIG.

  As shown in FIG. 10B, the light source 12 includes a purple LED 12_v and a white LED 12_w. Purple LED12_v is arrange | positioned facing white LED12_w, radiates | emits purple radiated light L_v, and irradiates white LED12_w.

  The white LED 12_w includes an LED chip 12c whose surface is coated with a resin 12r and a package 12p that houses the LED chip 12c.

  The LED chip 12c emits blue light having a half width of about 20 nm centered at 450 nm. The resin 12r includes a powdery fluorescent substance and a scattering substance. The powdery fluorescent substance is excited by a part of the emitted light from the LED chip 12c, and emits fluorescence in a wavelength band of about 150 nm at a half-width of about 600 nm. Radiate. The other part of the LED radiation is diffused by the resin 12r. Therefore, as shown in FIG. 11, the white LED 12_w emits white diffused radiation LA composed of blue radiation and fluorescence.

  Further, the resin 12r scatters and reflects the purple radiated light L_v by the fluorescent material and the scattering material, and re-radiates it as the diffused light of the light distribution 12g.

  As the scattering material contained in the resin 12r, it is preferable to employ, for example, titanium oxide powder from the viewpoint of enhancing scattering properties.

  FIG. 11 shows the spectral distribution of the light source 12 according to the fifth embodiment. In FIG. 11, the vertical axis represents relative intensity, and the horizontal axis represents wavelength (nm).

  As shown in FIG. 11, white diffused radiation light LA and scattered reflected light LB of purple radiation light L_v are emitted from the LED chip 12c. The scattered reflected light LB is light having a wavelength band of 430 nm or less that is not covered by the white diffuse radiation LA. In addition, LB 'has shown the fluorescence by purple emitted light L_v.

  Therefore, the light source 12 in FIG. 10B can cover the entire wavelength band (400 to 700 nm) of visible light in the spectral distribution. Moreover, in this Embodiment, the plane mirror 3 is arrange | positioned as shown to FIG. 10 (A). As a result, even if the distance between the illumination optical system and the sample surface 1 fluctuates over the entire wavelength band of visible light, a change in illuminance can be suppressed. Further, since the light source 12 composed of one white LED 12_w and one purple LED 12_v is employed, a 45 ° c: 0 ° geometry is obtained by guiding light beams in a plurality of directions to the sample surface 1 with one light source 12. The reflection characteristic measuring apparatus is configured. Therefore, a highly efficient and low-cost reflection characteristic measuring device can be provided.

  In the present embodiment, a total of three light distributions including two light distributions 12d and 12f due to blue radiation light and fluorescence included in the diffused radiation light LA and one light distribution 12g due to the scattered reflected light LB are included. It is. Therefore, the offset angle δ with respect to the light distribution in which the deviation to the light distribution main axis among the three light distributions becomes maximum may be set as the offset angle δ of the light source 12.

  When one light source 12 is used, the light distribution may vary depending on the direction of light emitted from the light source 12. In this case, an offset angle δ corresponding to the light distribution in the corresponding azimuth may be set for each plane mirror 3.

  The technical features of the above embodiment can be summarized as follows.

(1) The illumination optical system includes a light source that emits surface light with non-Lambertian light distribution, and illuminates the sample surface at an angle of 45 ° from the normal of the sample surface passing through the center of the sample surface to be measured. In the optical system, the light source is substantially equal in distance from the center of the light emitting surface of the light source to the normal line of the sample surface and from the center of the light emitting surface to a plane including the sample surface, A light distribution principal axis perpendicular to the light emitting surface of the light source is disposed at a predetermined offset angle with respect to the normal line of the sample surface, and the offset angle is determined so that the sample surface is normal to the sample surface. It has an angle that suppresses a change in illuminance on the sample surface when it changes in direction.

  According to this configuration, even when a non-Lambertian light source such as an LED is used, a change in illuminance on the sample surface due to a change in the distance between the illumination optical system and the sample surface can be suppressed. In addition, when this illumination optical system is applied to a reflection characteristic measuring apparatus, an error in the spectral reflectance coefficient of the sample surface due to a variation in the distance between the illumination optical system and the sample surface, and a color value calculated from the spectral reflectance coefficient The error can be suppressed.

  (2) The offset angle (δ) is such that the change rate of the light distribution of the light source at an angle of 45 ° −δ with respect to the light distribution main axis is a change at an angle of 45 ° with respect to the light distribution main axis of the Lambert light distribution. It is preferable that the angle is set to be substantially equal to the rate.

  According to this configuration, even when a non-Lambertian light source such as an LED is used, a change in illuminance on the sample surface due to a change in the distance between the illumination optical system and the sample surface can be suppressed.

  (3) The offset angle is preferably an angle within an incident surface including a normal line of the light emitting surface and the light source.

  According to this configuration, since the light distribution main axis is included in the incident surface and the offset angle is set in the incident surface, the offset angle can be easily set.

  (4) The offset angle changes in illuminance on the sample surface when the displacement in the direction of the normal of the sample surface can be assumed with respect to the illuminance on the sample surface at the initial position by the light source. It is preferable that the angle be a minimum.

  According to this configuration, even if the variation in the distance between the illumination optical system and the sample surface varies within a possible range of distance, the change in the illuminance on the sample surface can be minimized. In addition, when this illumination optical system is applied to a reflection characteristic measuring apparatus, an error in the spectral reflectance coefficient of the sample surface due to a variation in the distance between the illumination optical system and the sample surface, and a color value calculated from the spectral reflectance coefficient The error can be suppressed.

  (5) It is preferable that the light sources are a plurality of light sources arranged on a circumference centering on a direction of a normal line of the sample surface.

  According to this configuration, since the sample surface is irradiated with a 45 ° c: 0 ° geometry, the influence of the inclination and anisotropy of the sample surface on the measurement value can be suppressed.

  (6) It further includes a plane mirror disposed between the sample surface and the light source, and the light source is disposed with the light distribution main axis aligned with the direction of the normal line, and performs surface emission with non-Lambertian light distribution. A light source and a light source image symmetric with respect to the reflecting surface of the plane mirror, wherein the plane mirror is such that a light distribution principal axis perpendicular to the light emitting surface of the light source image is inclined by the offset angle from a normal line of the sample surface It is preferable to arrange | position.

  According to this configuration, the light emitted from the real light source having the non-Lambertian light distribution arranged so that the light distribution main axis coincides with the direction of the normal line of the sample surface is reflected by the plane mirror, and at an angle of 45 °. Even an illumination optical system that irradiates the sample surface can suppress a change in illuminance on the sample surface due to a variation in the distance between the actual light source and the sample surface.

  (7) The offset angle is the illuminance of the sample surface when the displacement in the direction of the normal of the sample surface can be assumed with respect to the illuminance of the sample surface at the initial position by the light source image. An angle that minimizes the change is preferred.

  According to this configuration, it is possible to minimize the change in the illuminance on the sample surface when the distance variation between the light source and the sample surface varies within a possible distance range. In addition, when this illumination optical system is applied to a reflection characteristic measuring apparatus, an error in the spectral reflectance coefficient of the sample surface due to a variation in the distance between the illumination optical system and the sample surface, and a color value calculated from the spectral reflectance coefficient The error can be suppressed.

  (8) The plane mirror is arranged such that the reflection surface is orthogonal to an incident surface including the light source image and the normal line of the light source surface of the real light source, and is inclined by δ / 2 with respect to the normal line of the sample surface. When the distance between the sample surface and the real light source is D, the distance from the center of the reflection surface to the normal line of the light emission surface of the real light source is from the center of the reflection surface to the sample surface. It is preferable to be equal to the distance and D / (cot (45 ° −δ) +1).

  According to this configuration, since the plane mirror is arranged as described above, it is possible to suppress a change in the illuminance on the sample surface due to a variation in the distance between the illumination optical system and the sample surface.

  (9) In the plane mirror, it is preferable that the reflection surface is larger than an incident area on the reflection surface of the total luminous flux from the light source image toward the measurement region of the sample surface.

  According to this configuration, it is possible to reflect the total luminous flux reaching the sample surface from the light source image. As a result, the illuminance on the sample surface can be made to be strictly proportional to the square of the distance between the light source image and the sample surface, and the change in the illuminance on the sample surface due to the variation in the distance between the illumination optical system and the sample surface can be calculated as expected. Can be suppressed.

  (10) It is preferable that a plurality of the plane mirrors are arranged around the normal line of the light emitting surface of the real light source.

  According to this configuration, since a plurality of plane mirrors are arranged around the normal line of the light emitting surface of the actual light source, illumination optics with a 45 ° c: 0 ° geometry that is not easily affected by the inclination or anisotropy of the sample surface. A system can be constructed. Moreover, the sample surface can be illuminated with a single light source using light beams in a plurality of directions, and the utilization efficiency of the light beams can be improved. For this reason, it is possible to reduce the change in illuminance due to the variation in the distance between the illumination optical system and the sample surface, and to realize low power consumption, low heat generation, and low cost.

  (11) It is preferable that the real light source has a different light distribution according to an orientation, and each of the plane mirrors is set with the offset angle according to the light distribution in the corresponding orientation of the real light source.

  According to this configuration, even if a non-Lambertian light source having a different light distribution depending on the azimuth is used, a change in illuminance on the sample surface due to a variation in the distance between the illumination optical system and the sample surface can be suppressed.

  (12) The light source irradiates light of a plurality of wavelength bands having different light distributions, and the offset angle has an offset angle in a light distribution having a maximum deviation from the light distribution main axis among the plurality of light distributions. It is preferably set.

  According to this configuration, even when a light source that emits a plurality of light distributions according to the wavelength band is adopted, the light distribution is set so that the bias to the light distribution main axis is the maximum among the plurality of light distributions. Since the offset angle of the light source is set at the offset angle, the change in illuminance on the irradiation surface accompanying the variation in the distance between the illumination optical system and the sample surface can be minimized over all wavelengths.

  (13) It is preferable that the light source is a white light emitting diode, and the white light emitting diode includes a blue light emitting diode and one or more kinds of fluorescent materials excited by radiated light from the blue light emitting diode.

  According to this configuration, even when a white LED including a blue light emitting diode and one or more kinds of fluorescent materials excited by light emitted from the blue light emitting diode is used, the illumination optical system and the irradiation surface It is possible to minimize the change in illuminance on the irradiated surface due to the distance variation between the two. Moreover, since such white LED is low-cost and highly efficient, power consumption and heat generation can be suppressed, and a low-cost illumination optical system can be configured. In addition, the light source has a long life, and the service cost can be reduced by extending the replacement interval of the light sources. In particular, it is possible to increase the merit when the reflection characteristic measuring apparatus to which the illumination optical system is applied is mounted on a color printer.

  (14) The reflection characteristic measuring apparatus receives light reflected from the illumination optical system and the light source of the illumination optical system when the sample surface is illuminated from the normal direction of the sample surface. An optical system; and a spectroscopic unit that measures reflection characteristics of the sample surface based on the reflected light received by the light receiving optical system.

  According to this configuration, even when a non-Lambertian light distribution light source is employed, a change in illuminance on the sample surface due to a variation in the distance between the illumination optical system and the sample surface can be suppressed. The error of the spectral reflectance coefficient and the error of the color value calculated from the spectral reflectance coefficient can be suppressed.

(15) In the illumination method using the reflection characteristic measuring apparatus, the sample surface is illuminated at an angle of 45 ° from the normal direction of the sample surface passing through the center of the sample surface to be measured. Is an illumination method for measuring the reflection characteristics of the sample surface from the direction of the normal of the sample surface, and a light source that emits surface light by non-Lambertian light distribution is provided on the light emitting surface of the light source. A first step in which the distance from the center to the normal of the sample surface and the distance from the center of the light emitting surface to a plane including the sample surface are substantially equal; and perpendicular to the light emitting surface of the light source And a second step of disposing a light distribution main axis at a predetermined offset angle (δ) with respect to a normal line of the sample surface, wherein the sample surface is normal to the sample surface. Have an angle that suppresses the change in illuminance on the sample surface when it fluctuates in the direction. One.

  According to this configuration, the same effect as (1) can be obtained.

Claims (15)

An illumination optical system that includes a light source that emits a surface with non-Lambertian light distribution and illuminates the sample surface at an angle of 45 ° from a normal to the sample surface passing through the center of the sample surface to be measured,
In the light source, the distance from the center of the light emitting surface of the light source to the normal of the sample surface is substantially equal to the distance from the center of the light emitting surface to the plane including the sample surface, and the light emission of the light source A light distribution principal axis perpendicular to the surface is disposed at a predetermined offset angle with respect to the normal of the sample surface;
The offset angle is an illumination optical system having an angle that suppresses a change in illuminance on the sample surface when the sample surface fluctuates in a direction normal to the sample surface.   The offset angle (δ) is substantially equal to the change rate of the light distribution of the light source at an angle of 45 ° −δ with respect to the light distribution main axis at a 45 ° angle with respect to the light distribution main axis of the Lambert light distribution. The illumination optical system according to claim 1, wherein the angles are set to be equal to each other.   The illumination optical system according to claim 1, wherein the offset angle is an angle within an incident surface including a normal line of the light emitting surface and the light source.   The offset angle minimizes a change in the illuminance of the sample surface when the displacement in the direction of the normal of the sample surface becomes a maximum value with respect to the illuminance of the sample surface at the initial position by the light source. The illumination optical system according to claim 1, wherein the illumination optical system is at an angle to be   The illumination optical system according to claim 1, wherein the light sources are a plurality of light sources arranged on a circumference centering on a direction of a normal line of the sample surface. A flat mirror disposed between the sample surface and the light source;
The light source includes a real light source that is arranged with a light distribution principal axis coincident with a direction of a normal line of the sample surface, emits light by non-Lambertian light distribution, and a light source image that is symmetrical with respect to the reflection surface of the plane mirror. ,
2. The illumination optical system according to claim 1, wherein the plane mirror is disposed such that a light distribution principal axis perpendicular to a light emitting surface of the light source image is inclined by the offset angle from a normal direction of the sample surface.   The offset angle is a minimum change in the illuminance of the sample surface when the displacement in the direction of the normal of the sample surface becomes a maximum value with respect to the illuminance of the sample surface at the initial position by the light source image. The illumination optical system according to claim 6, wherein the angle is an angle to be adjusted. The plane mirror is arranged such that the reflecting surface is orthogonal to an incident surface including the light source image and the normal line of the light source surface of the real light source, and is inclined by δ / 2 with respect to the normal line of the sample surface.
When the distance between the sample surface and the real light source is D, the distance from the center of the reflection surface to the normal line of the light emission surface of the real light source is the distance from the center of the reflection surface to the sample surface. The illumination optical system according to claim 6, which is equal and D / (cot (45 ° −δ) +1).   The illumination optical system according to claim 6, wherein the plane mirror has a reflecting surface larger than an incident area on the reflecting surface of a total luminous flux from the light source image toward the measurement area of the sample surface.   The illumination optical system according to claim 6, wherein a plurality of the plane mirrors are arranged around a normal line of a light emitting surface of the real light source. The real light source has a different light distribution depending on the orientation,
The illumination optical system according to claim 10, wherein each of the plane mirrors has the offset angle set according to light distribution in a corresponding direction of the real light source. The light source emits light of a plurality of wavelength bands having different light distributions,
The illumination optical system according to any one of claims 1 to 11, wherein the offset angle is set to a light distribution having a maximum deviation from the light distribution main axis among a plurality of light distributions. The light source is a white light emitting diode;
The white light emitting diode is
A blue light emitting diode,
The illumination optical system according to any one of claims 1 to 12, further comprising at least one fluorescent material that is excited by radiation emitted from the blue light emitting diode. The illumination optical system according to any one of claims 1 to 13,
A light receiving optical system that receives reflected light when the light source of the illumination optical system illuminates the sample surface from the direction of the normal of the sample surface;
A reflection characteristic measuring apparatus comprising: a spectroscopic unit that measures reflection characteristics of the sample surface based on reflected light received by the light receiving optical system. Illuminating the sample surface at an angle of 45 ° from the normal direction of the sample surface passing through the center of the sample surface to be measured, and receiving reflected light from the sample surface from the normal direction of the sample surface; An illumination method for measuring the reflection characteristics of the sample surface,
For a light source that emits a surface by non-Lambertian light distribution, the distance from the center of the light emitting surface of the light source to the normal of the sample surface is substantially equal to the distance from the center of the light emitting surface to a plane including the sample surface. A first step of arranging so that
A second step of disposing a light distribution main axis perpendicular to the light emitting surface of the light source at a predetermined offset angle (δ) with respect to a normal line of the sample surface,
The offset angle is an illumination method having an angle that suppresses a change in illuminance on the sample surface when the sample surface changes in a direction of a normal line of the sample surface.

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