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Optical measuring deviceOptical measuring device description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070242264, Optical measuring device. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001]This is a continuation of International Application No. PCT/JP2006/307776, with an international filing date of Apr. 12, 2006, the contents of which are hereby incorporated by reference. BACKGROUND OF THE INVENTION [0002]1. Field of the Invention [0003]The present invention relates to an optical measuring device that can measure the total luminous flux of a light source. [0004]2. Description of the Related Art [0005]Among various optical measuring devices, a total luminous flux measuring device can measure the total luminous flux of a surface emitting light source such as a display with respect to a total luminous flux standard lamp, which is a cylindrical light source. A typical conventional total luminous flux measuring device includes a perfect integrating sphere, of which the inner surface is coated with a perfectly diffuse reflective material such as barium sulfate. A sample lamp, which is the object of measurement, is arranged at the center of the integrating sphere and its luminous flux is measured through an observation window, which is located on the surface of the integrating sphere. A baffle is arranged between the observation window and the sample lamp such that the light emitted from the sample lamp does not enter the observation window directly. By measuring and comparing the luminous flux of the sample lamp to the known total luminous flux of a total luminous flux standard lamp using such a sphere photometer, the total luminous flux of the sample lamp can be obtained. [0006]In such a sphere photometer, the sample lamp needs to be lit at the center of the integrating sphere, thus requiring a supporting member to fix the sample lamp at the center of the integrating sphere. However, since such a supporting member and the lamp itself absorb light to cause a measurement error, the supporting member is often coated with the same material as that applied onto the inner surface of the integrating sphere. [0007]According to a proposed method, a light source for measuring self-absorption is lit on the inner surface of the integrating sphere, and the self-absorption of the supporting member and the sample lamp is calculated as the ratio of the output of the measuring device with the supporting member and the sample lamp to that of the measuring device without them. Actually, however, the lamp supporting member often serves as a wire duct to light the lamp as well and is often fixed on the integrating sphere. That is why the self-absorption ratio of the only the sample lamp is usually calculated (see JIS C7607-1991, Method for Measuring the Total Luminous Flux of Light Measuring Standard Electrical Discharge Lamp, Appendix: How to Calculate Correction Coefficient, 2. How to Define Self Absorption Correction Coefficient k2 according to Various Lamp Shapes or Sizes). [0008]On the other hand, the spatial and spectral distributions of the light emitted from the sample lamp are different from those of the total luminous flux standard light source, and therefore, the self-absorption of the lamp supporting member and the sample lamp has a non-negligible value. [0009]To overcome such a problem, a novel total luminous flux measuring device, including a hemisphere and a plane mirror, was proposed in Japanese Patent Application Laid-Open Publication No. 6-167388 (see FIG. 1). [0010]The device disclosed in Japanese Patent Application Laid-Open Publication No. 6-167388 (see FIG. 1) is fabricated by providing an integrating hemisphere 2, of which the inner surface is coated with a light diffuse reflective material 1 such as barium sulfate, and closing the opening of this integrating hemisphere 2 with a plane mirror 3 as shown in FIG. 8. A hole 5 has been cut through the plane mirror 3 so as to be located at the center of curvature of the integrating hemisphere and to receive a light source 4 under measurement. By lighting the light source 4 under measurement inside the integrating hemisphere 2, a virtual image of the inner wall of the integrating hemisphere 2 and the light source 4 under measurement is formed by the plane mirror 3. As a result, the light source 4 under measurement and a virtual image thereof are both lit inside an integrating sphere having the same radius as the integrating hemisphere. In this manner, the total luminous flux of the two light sources, consisting of the light source 4 under measurement and a virtual image thereof, is measured by a photodetector 6. [0011]In this device, the lamp supporting member (lighting jig) 8 is arranged outside of the integrating space, and therefore, the total luminous flux measured is not affected by the self-absorption produced by the lamp supporting member 8. Consequently, high measuring accuracy is realized without performing any complicated process to correct the self-absorption of the lamp supporting member 8, for example. Also, since the integrating space is only a half of a full integrating sphere, the photodetector 6 can have doubled illuminance at its light receiving window. As a result, the SNR can be increased in measuring the total luminous flux. [0012]According to the arrangement shown in FIG. 8, however, the baffle 7 needs to cut off not only the light coming directly from the light source 4 under measurement but also the light coming directly from the virtual image of the light source 4 under measurement. That is why the size of the baffle 7 has to be more than doubled compared to the situation where only the light source 4 under measurement is lit inside a full integrating sphere as will be described later. The baffle 7 inside the integrating sphere partially cuts off the optical path of the reflected light inside the integrating sphere. However, since the baffle itself absorbs light, the measurement error would increase just like the lamp supporting member arranged in the full integrating sphere. [0013]Hereinafter, the principle of measurement to be done using the integrating sphere and the error caused due to the self-absorption of the baffle will be described in detail. [0014]First, the principle of measurement to be done using the integrating sphere will be described with reference to FIG. 9, which shows, by way of a planar model, how the integrating sphere works. [0015]Suppose a light source 4 is arranged at the center of an integrating sphere with a radius r and an infinitesimal surface element A on the wall of the integrating sphere has been illuminated at a luminous intensity I.sub.0(.alpha.) by the light source 4 in the direction defined by an angle .alpha.. In that case, the illuminance E.sub.a of the infinitesimal surface element A on the integrating sphere wall is represented by the following Equation (1): E.sub.a=I.sub.0(.alpha.)/r.sup.2 (1) [0016]On the inner wall of the integrating sphere, perfectly diffuse reflection is produced at a reflectance .rho.. Supposing the infinitesimal surface element A on the inner wall has an area dS, the luminous flux .phi..sub.a of the light reflected from the infinitesimal surface element A is given by the following Equation (2): a=.rho.E.sub.adS (2) [0017]Suppose there is an infinitesimal surface element B on the inner wall of the integrating sphere, which defines an angle .theta. with respect to a normal to the infinitesimal surface element A. Since the infinitesimal surface element A is a perfectly diffuse reflective surface, the luminous intensity I.sub.a(.theta.) in the direction from the infinitesimal surface element A toward the infinitesimal surface element B is calculated by the following Equation (3): I.sub.a(.theta.)=.phi..sub.acos .theta./.pi. (3) [0018]Since the surface B is located on the inner wall of the integrating sphere, the light directed toward the surface B with the luminous intensity I.sub.a(.theta.) has an angle of incidence .theta. and the distance from the infinitesimal surface element A to the infinitesimal surface element B is 2rcos .theta.. Therefore, at the surface B, the light with the luminous intensity I.sub.a(.theta.) has the illuminance E.sub.ab given by the following Equation (4): E ab = I a ( .theta. ) cos .theta. / ( 2 r cos .theta. ) 2 = .phi. a / ( 4 .pi. r 2 ) = .rho. I 0 ( .alpha. ) dS / ( 4 .pi. r 4 ) ( 4 ) [0019]As can be seen easily from Equation (4), the light reflected from the infinitesimal surface element A illuminates any portion of the inner wall of the integrating sphere with light with a uniform illuminance irrespective of the angle .theta. of the light that has been reflected from the infinitesimal surface element A. Since the integrating sphere has an internal surface area of 4.pi.r.sup.2, the very small area dS can be calculated by the following Equation (5) using a very small solid angle d.OMEGA.: Continue reading about Optical measuring device... Full patent description for Optical measuring device Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Optical measuring device patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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