Abstract:
A stored light intensity measurement device capable of measuring an afterglow intensity from a light storing sign in a simple way, even if the light storing sign is provided on walls or risers of stairs in facilities or underground shopping mall. The stored light intensity measurement device comprising the light measuring unit configured o measure afterglow from a part of a light storing section on a light storing sign, and calculation means for calculating an afterglow intensity from the light storing sign based on the measured results.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims the benefit of Japanese patent application number 2005-367685, filed in Japan on Dec. 21, 2005, the subject matter of which is hereby incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     (1) Field of the Invention  
         [0003]     The present invention relates to a stored light intensity measurement device for measuring afterglow intensity of a light storing sign.  
         [0004]     (2) Description of the Related art  
         [0005]     When the earthquake or the like causes a power failure at night, a self-generation of electricity type or battery-powered type pilot display light is to light in an underground passage, in a passage in a building, or in the subway yard. However, there are occurrences when the self-generation of electricity does not always work at the earthquake, and the battery-powered pilot display light does not light at the emergency due to failing the maintenance of the battery of the pilot display light.  
         [0006]     Therefore, Japanese government promotes an installation of light storing signs, which keep the luminescence in a specific period after the power failure without supplying energy from outside, on a wall and a riser of stairs in the above-mentioned sites. The light storing sign is a sign board made up of synthetic resin, ceramic, or glass, and of which surface is processed by the light storing material and is given a safety sign design with coloring materials.  
         [0007]     The light storing material can absorb light such as sunlight or fluorescent light, and store the energy, and release the stored energy as visible light. The light storing sign using the light storing material is visible due to its phosphorescence in dark environment, and it is also visible even when ambient darkness occurs due to the power failure.  
         [0008]     The phosphorescence of the light storing sign fades away and becomes invisible with the lapse of time. Recently, in case of strontium aluminate or calcium aluminate that are used as the light storing material, the visible state will last for approximate 10 hours in total darkness. In case of zinc sulfide, the visible state will last only for a few hours.  
         [0009]     In order that the sign is useful in darkness, the sign should have necessary luminance after a predetermined time lapsed. Japanese Industrial Standards Z9107 regulates the light storing sign for communicating or displaying for caution, indication or information for evacuation. That is to say, the luminance of the phosphorescence requires 24 mcd/m 2  and more after 20 minutes from the light interception.  
         [0010]     In order to measure the afterglow intensity of the light storing sign, the luminance meter like the spot-meter is useful, as disclosed in Japanese Patent Unexamined-Publication No. 07-011250A. For instance, the light storing sign is placed in total darkness for hours before the measurement is performed, and then a predetermined illuminance light is irradiated thereon to store the energy of light. After that, the light storing sign is moved again in darkness, and the afterglow intensity of the light storing sign is measured by the luminance meter.  
       SUMMARY OF THE INVENTION  
       [0011]     The above method is available for measuring the afterglow intensity from the storing sign before the sign is installed. However, it is difficult to measure the afterglow intensity after the sign is installed. The sign is placed in the facility or underground shopping mall mostly, and in order to measure the afterglow intensity in such case, the facility or underground must be unilluminated.  
         [0012]     The present invention is suggested in view of the above-mentioned subject in the prior art, and has an object to provide an stored light intensity measurement device capable of easily measuring the afterglow intensity from the light storing sign regardless of the environment on which the light storing sign is placed.  
         [0013]     In order to achieve the above object, the present invention provides a stored light intensity measurement device comprising: a light measurement unit configured to measure afterglow from a part of light stored section on a light storing sign; and calculation means for calculating an afterglow intensity from the light storing sign based on the measured results.  
         [0014]     In accordance with a preferred embodiment, the calculation means calculates the afterglow intensity after a predetermined time lapsed from beginning light interception based on reciprocals of the afterglow intensity measured for a period in the predetermined time lapsed. In employing such configuration, the stored light intensity measurement device can measure the stored light intensity in a short time, and makes it possible to facilitate the maintenance of the light storing sign. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:  
         [0016]      FIG. 1  is a graph representing actual measured values of afterglow intensity corresponding to a plurality of samples as light storing signs.  
         [0017]      FIG. 2  is a graph representing logarithms of the actual measured values in  FIG. 1 .  
         [0018]      FIG. 3  is a graph representing reciprocals of the actual measured values in  FIG. 1 .  
         [0019]      FIG. 4  is a graph representing actual measured values of afterglow intensity of which sampling conditions vary.  
         [0020]      FIG. 5  is a graph representing reciprocals of the actual measured values in  FIG. 4 .  
         [0021]      FIG. 6  is a graph representing actual measured values of afterglow intensity on different sections of the light storing sign.  
         [0022]      FIG. 7  is a light storing sign according to the embodiment of the present invention.  
         [0023]      FIG. 8  is an external view of a stored light intensity measurement device of the invention.  
         [0024]      FIG. 9  is an enlarged view of an outer appearance of a light measurement unit.  
         [0025]      FIG. 10  is a sectional view of a light measurement unit.  
         [0026]      FIG. 11  is a diagram for explaining the outline of electric structure of the stored light intensity measurement device.  
         [0027]      FIG. 12  is a functional block diagram of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]     The embodiments of the present invention are discussed hereinafter in accordance with attached drawings. In the embodiments, the present invention is embodied as a stored light intensity measurement device for measuring the afterglow intensity of light storing signs.  
         [0029]      FIG. 7  shows a light storing sign according to the embodiment of the present invention. The light storing sign  103  is a rectangular plate, on which colored sections  108  painted with colored material and light storing sections  109  applied with light storing material are provided. The colored sections  108  are formed by painting an arrow indicating an evacuation way together with an necessary pictograph, and the light storing sections  109  are sections on which the arrow and the pictograph are not painted. In this embodiment, the device measures afterglow from any part of the light storing section  109 . The structure of the device for measuring the afterglow intensity on any part of the light storing sign will be described briefly later.  
         [0030]     Light storing sign samples used in this embodiment are six (A- 1 , A- 2 , A- 3 , A- 4 , B- 1 , and C- 1 ), and  FIG. 1  shows afterglow intensity attenuation characteristics of respective measurement sections after the light interception. The afterglow intensity is set to a vertical axis and light interception time (minute) is set to a horizontal axis. The light storing sign samples A- 1  to A- 4  are resin plates on which the light storing material is applied, the light storing sign sample B- 1  is also the resin plate on which the light storing material is applied like the samples A- 1  to A- 4 , and the light storing sign sample C- 1  is a ceramic plate on which the light storing material is applied.  
         [0031]      FIG. 2  is a graph representing the same measurement result as in  FIG. 1  by logarithm index. This kind of the light storing material is well known to show the exponential function attenuation characteristics as disclosed in Japanese laid-open Publication No. 07-11250A. Providing that the intensity has the exponential function attenuation characteristics, the afterglow intensity L 20  after 20 minutes from the light interception on a specific section of the light storing sign can be calculated by a following equation (1), using the intensity values measured for a predetermined period after the light interception, for example, from 3 minutes to 5 minutes after the light interception (because the values measured for 3 minutes after the light interception are considered as unstable data). 
   L   20   =−a  log  e   t   +b  ( a : coefficient,  b : constant)  (1)  
         [0032]     However, when various light storing materials are applied on the light storing sign used in the embodiment (that is to say, the materials are applied thinly over the plate), it is possible to understand from  FIG. 2  that the afterglow intensity does not show the exponential function attenuation characteristics. Table 1 shows the predicted afterglow intensity values after 20 minutes from the light interception on the specific section on the light storing sign, which are predicted (calculated) based on the measured intensity values from 3 minutes to 5 minutes from the light interception by means of the exponential function. The proportion of the predicted intensity values to the actual measured values indicates 50% to 80% deviation.  
                                                   TABLE 1                           Predicted intensity of light-energy storing samples after 20 min.       from light interception, calculated using exponential function       Result Predicted from intensity of samples measured       from 3 min. to 5 min. after light interception                        Proportion of           Actual measured   Predicted   predicted intensity           intensity after 20 min.   intensity after 20 min.   to measured           from light   from light   intensity after 20 min.           interception   interception   from light       Sample   [mcd/m2]   [mcd/m2]   interception [%]                    Resin sample A-1   243.0   59.3   −75.6       Resin sample A-2   215.0   49.1   −77.2       Resin sample A-3   180.0   66.5   −63.1       Resin sample A-4   156.0   29.5   −81.1       Resin sample B-1   107.0   19.0   −82.2       Ceramic sample C-1   197.0   87.0   −55.8       Average (Ave.)           −72.5       Standard deviation (S.D.)           9.7                  
 
         [0033]      FIG. 3  is a graph representing reciprocals of the actual measured values for every sample. It is understood about every sample that the reciprocal of the measured value (the vertical axis) vs. the time (the horizontal axis) approximates a straight line (a linear expression). Therefore, the afterglow intensity at a time t after the light interception is expressed by the following linear equation (2).  
               L   =     1     α   +     β   ⁢           ⁢   t           ⁢     
     ⁢   α   ,     β   ⁢     :     ⁢           ⁢   constant             (   2   )               
         [0034]     When the predicted afterglow intensity after 20 minutes from the light interception is calculated by the above linear approximate equation based on the actual measured values from 3 minutes to 5 minutes after the light interception, Table 2 represents the actual measured intensity values, the predicted afterglow intensity values, and the deviation proportion (%) of both values. Since there is the time that cannot be approximated by the straight line just after the light interception, the data measured for 3 minutes just after the light interception is excluded. In result, there is a very little error between the calculated afterglow intensity after 20 minutes from the light interception and the actual measured intensity (−0.9% to +3.4%).  
                                                   TABLE 2                           Predicted intensity of light-energy storing sign samples after 20 min.       from light interception, calculated using the reciprocal of measured intensity       Result predicted from intensity of samples measured       from 3 min. to 5 min. after light interception                        Proportion of               Predicted   predicted           Actual measured   intensity after   intensity to           intensity after 20 min.   20 min. from   measured           from light   light   intensity after 20 min.           interception   interception   from light       Sample   [mcd/m2]   [mcd/m2]   interception [%]                    Resin sample A-1   243.0   240.7   −0.9       Resin sample A-2   215.0   216.9   0.9       Resin sample A-3   180.0   186.3   3.5       Resin sample A-4   156.0   158.2   1.4       Resin sample B-1   107.0   111.1   3.8       Ceramic sample C-1   197.0   203.7   3.4       Average (Ave.)           2.0       Standard deviation (S.D.)           1.7                  
 
         [0035]     When the sampling time varies, Table 3 represents the actual measured value after 20 minutes from the light interception, the deviation between the actual measured value and the predicted value, and the deviation percentage of both values. There are 6 cases of the sampling times between ‘a sampling time from 2 minutes to 3 minutes after the light interception’ and ‘a sampling time from 3 minutes to 5 minutes after the light interception’. The deviation percentage of both values ranges within plus or minus several percentages. It proves no problem in practical use.  
                                                                                                                                                           TABLE 3                       Predicted intensity of light-energy storing sign samples after 20 min. from light interception, calculated using the       reciprocal of measured intensity (calculation based on data at arbitrary time from 2 min. to 5 min. after light interception)                                    Sample                Resin sample A-1   Resin sample A-2   Resin sample A-3                Intensity   Deviation   Proportion   Intensity   Deviation   Proportion   Intensity   Deviation   Proportion           [mcd/m2]   [mcd/m2]   [%]   [mcd/m2]   [mcd/m2]   [%]   [mcd/m2]   [mcd/m2]   [%]               Measured   243           215           180       intensity       Predicted   232.4   −10.6   −4.4   210.1   −4.9   −2.3   182.7   2.7   1.5       intensity 1       Predicted   234.5   −8.5   −3.5   213.2   −1.8   −0.8   184.1   4.1   2.3       intensity 2       Predicted   235.9   −7.1   −2.9   213.6   −1.4   −0.7   185.2   5.2   2.9       intensity 3       Predicted   237.7   −5.3   −2.2   215   0.0   0.0   185.5   5.5   3.1       intensity 4       Predicted   240.4   −2.6   −1.1   216.7   1.7   0.8   187.5   7.5   4.2       intensity 5       Predicted   240.7   −2.3   −0.9   216.9   1.9   0.9   186.3   6.3   3.5       intensity 6                        Sample                Resin sample A-4   Resin sample B-1   Ceramic sample C-1                Intensity   Deviation   Proportion   Intensity   Deviation   Proportion   Intensity   Deviation   Proportion           [mcd/m2]   [mcd/m2]   [%]   [mcd/m2]   [mcd/m2]   [%]   [mcd/m2]   [mcd/m2]   [%]               Measured   156           107           197       intensity       Predicted   155.6   −0.4   −0.3   110.3   3.3   3.1   197.9   0.9   0.5       intensity 1       Predicted   155.9   −0.1   −0.1   110.4   3.4   3.2   199.9   2.9   1.5       intensity 2       Predicted   157.1   1.1   0.7   110.4   3.4   3.2   201.3   4.3   2.2       intensity 3       Predicted   157.4   1.4   0.9   110.8   3.8   3.6   202.1   5.1   2.6       intensity 4       Predicted   159.1   3.1   2.0   110.6   3.6   3.4   205.3   8.3   4.2       intensity 5       Predicted   158.2   2.2   1.4   111.1   4.1   3.8   203.7   6.7   3.4       intensity 6                 Deviation [mcd/m2]: Deviation between estimated intensity and measured intensity after 20 min. from light interception            Proportion[%]: Proportion of estimated intensity to measured intensity after 20 min. from light interception            Measured intensity: Afterglow intensity actually measured after 20 min. from light interception            Predicted intensity 1: Predicted intensity calculated based on data measured from 2 to 3 min.            Predicted intensity 2: Predicted intensity calculated based on data measured from 2 to 3.5 min.            Predicted intensity 3: Predicted intensity calculated based on data measured from 2 to 4 min.            Predicted intensity 4: Predicted intensity calculated based on data measured from 2 to 5 min.            Predicted intensity 5: Predicted intensity calculated based on data measured from 3 to 4 min.            Predicted intensity 6: Predicted intensity calculated based on data measured from 3 to 5 min.            Conditions:            (1) Light-energy storing condition: illuminance 200 lx for 1 hr.            (2) Calculation of estimated intensity using measurement data for every 30 sec.             
 
         [0036]     Where the afterglow intensity of the sample A- 1  is measured at different storing conditions of light energy, the measurement result is shown in  FIG. 4 . The light storing conditions are an illuminance time before the light interception and the illuminance intensity. The storing conditions are five cases, that is, illuminance 50 lux for 20 minutes (condition A), illuminance 80 lux for 20 minutes (Condition B), illuminance 100 lux for 20 minutes (condition C), illuminance 100 lux for 1 hour (Condition D), and illuminance 1000 lux for 1 hour (condition E).  
         [0037]     Table 4 represents calculation results when the predicted afterglow intensity after 20 minutes are calculated based on the actual measured values shown in  FIG. 4  using data measured for the period expressed in the left column of Table 4, and the calculation is based on the assumption that the attenuation approximates the exponential function. In each illminance condition (conditions A to E), the predicted value becomes around minus 80% of the actual measured value. It proves that those values are not available in practical use.  
         [0038]      FIG. 5  represents the reciprocals of the actual measured vales in  FIG. 4  in graphic form. Like  FIG. 3 , it can be understood that those values approximate the straight line (the linear equation) irrespective of the light storing conditions. When the predicted afterglow intensity after 20 minutes for the sample A- 1  are calculated based on the reciprocals of the afterglow intensity measured during a specific period until a predetermined time has lapsed from beginning of the light interception, Table 5 represents the predicted values for every light storing condition. The specific period until the predetermined time has lapsed from the light interception is six types of conditions in the same way as Table 2. Regardless of the respective light storing conditions and the sampling times, the deviation percentage between the predicted value and the actual measured value rages within −5 to +1.8. It proves there is no problem in practical use.  
                                                                                                                                                           TABLE 4                       Predicted intensity of light-energy storing sign samples A-1 after 20 min. from light interception, calculated using       exponential function, under different light-energy storing conditions (Calculation based on data at arbitrary time       from 2 min. to 5 min. after light interception)                                    Conditions                Illuminance 50 lx   Illuminance 80 lx   Illuminance 100 lx           for 20 min.   for 20 min.   for 20 min.                Intensity   Deviation   Proportion   Intensity   Deviation   Proportion   Intensity   Deviation   Proportion           [mcd/m2]   [mcd/m2]   [%]   [mcd/m2]   [mcd/m2]   [%]   [mcd/m2]   [mcd/m2]   [%]               Measured   102           156           194       intensity       Predicted   21.3   −80.7   −79.1   20   −136.0   −87.2   21.7   −172.3   −88.8       intensity 1       Predicted   23   −79.0   −77.5   23.7   −132.3   −84.8   26   −168.0   −86.6       intensity 2       Predicted   25.1   −76.9   −75.4   38.5   −117.5   −75.3   29.5   −164.5   −84.8       intensity 3       Predicted   30.4   −71.6   −70.2   35   −121.0   −77.6   37.9   −156.1   −80.5       intensity 4       Predicted   30.3   −71.7   −70.3   38.5   −117.5   −75.3   40.8   −153.2   −79.0       intensity 5       Predicted   37.7   −64.3   −63.0   47.2   −108.8   −69.7   51.7   −142.3   −73.4       intensity 6                        Conditions                Illuminance 100 lx   Illuminance 200 lx   Illuminance 1000 lx           for 1 hr.   for 1 hr.   for 1 hr.                Intensity   Deviation   Proportion   Intensity   Deviation   Proportion   Intensity   Deviation   Proportion           [mcd/m2]   [mcd/m2]   [%]   [mcd/m2]   [mcd/m2]   [%]   [mcd/m2]   [mcd/m2]   [%]               Measured   218           243           283       intensity       Predicted   24.8   −193.2   −88.6   19.4   −223.6   −92.0   14.8   −268.2   −94.8       intensity 1       Predicted   29.8   −188.2   −86.3   24.4   −218.6   −90.0   19.3   −263.7   −93.2       intensity 2       Predicted   34.4   −183.6   −84.2   29.4   −213.6   −87.9   23.4   −259.6   −91.7       intensity 3       Predicted   44.7   −173.3   −79.5   39.5   −203.5   −83.7   33.3   −249.7   −88.2       intensity 4       Predicted   48.8   −169.2   −77.6   47.7   −195.3   −80.4   39   −244.0   −86.2       intensity 5       Predicted   61.8   −156.2   −71.7   59.3   −183.7   −75.6   53.6   −229.4   −81.1       intensity 6                 Deviation [mcd/m2]: Deviation between predicted intensity and measured intensity after 20 min. from light interception            Proportion[%]: Proportion of predicted intensity to measured intensity after 20 min. from light interception            Measured intensity: Afterglow intensity actually measured after 20 min. from light interception            Predicted intensity 1: Predicted intensity calculated based on data measured from 2 to 3 min.            Predicted intensity 2: Predicted intensity calculated based on data measured from 2 to 3.5 min.            Predicted intensity 3: Predicted intensity calculated based on data measured from 2 to 4 min.            Predicted intensity 4: Predicted intensity calculated based on data measured from 2 to 5 min.            Predicted intensity 5: Predicted intensity calculated based on data measured from 3 to 4 min.            Predicted intensity 6: Predicted intensity calculated based on data measured from 3 to 5 min.            The predicted intensity was calculated using data measured for every 30 sec.            1. Afterglow intensity test for light-energy storing type pilot sign: illuminance 200 lx for 1 hr.            2. Illuminance in underground passage: 200 lx and more (under an ordinance of Tokyo Fire Defense Agency)               
         [0039]    
       
         
               
             
               
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                   
               
               
                 Predicted intensity of light-energy storing sign samples A-1 after 20 min. from light interception, calculated using the 
               
               
                 reciprocal of measured intensity, under different light-energy storing conditions (Calculation based on data at arbitrary 
               
               
                 time from 2 min. to 5 min. after light interception) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Conditions 
               
             
          
           
               
                   
                 Illuminance 50 lx 
                 Illuminance 80 lx 
                 Illuminance 100 lx 
               
               
                   
                 for 20 min. 
                 for 20 min. 
                 for 20 min. 
               
             
          
           
               
                   
                 Intensity 
                 Deviation 
                 Proportion 
                 Intensity 
                 Deviation 
                 Proportion 
                 Intensity 
                 Deviation 
                 Proportion 
               
               
                   
                 [mcd/m2] 
                 [mcd/m2] 
                 [%] 
                 [mcd/m2] 
                 [mcd/m2] 
                 [%] 
                 [mcd/m2] 
                 [mcd/m2] 
                 [%] 
               
               
                   
               
               
                 Measured 
                 102 
                   
                   
                 156 
                   
                   
                 194 
               
               
                 intensity 
               
               
                 Predicted 
                 96.7 
                 −5.3 
                 −5.2 
                 152.7 
                 −3.3 
                 −2.1 
                 193 
                 −1.0 
                 −0.5 
               
               
                 intensity 1 
               
               
                 Predicted 
                 95.9 
                 −6.1 
                 −6.0 
                 153.4 
                 −2.6 
                 −1.7 
                 193.8 
                 −0.2 
                 −0.1 
               
               
                 intensity 2 
               
               
                 Predicted 
                 96 
                 −6.0 
                 −5.9 
                 154.1 
                 −1.9 
                 −1.2 
                 193.2 
                 −0.8 
                 −0.4 
               
               
                 intensity 3 
               
               
                 Predicted 
                 97.3 
                 −4.7 
                 −4.6 
                 155.4 
                 −0.6 
                 −0.4 
                 194.1 
                 0.1 
                 0.1 
               
               
                 intensity 4 
               
               
                 Predicted 
                 95.5 
                 −6.5 
                 −6.4 
                 155.7 
                 −0.3 
                 −0.2 
                 192.5 
                 −1.5 
                 −0.8 
               
               
                 intensity 5 
               
               
                 Predicted 
                 98.2 
                 −3.8 
                 −3.7 
                 156.8 
                 0.8 
                 0.5 
                 194.6 
                 0.6 
                 0.3 
               
               
                 intensity 6 
               
               
                   
               
             
          
           
               
                   
                 Conditions 
               
             
          
           
               
                   
                 Illuminance 100 lx 
                 Illuminance 200 lx 
                 Illuminance 1000 lx 
               
               
                   
                 for 1 hr. 
                 for 1 hr. 
                 for 1 hr. 
               
             
          
           
               
                   
                 Intensity 
                 Deviation 
                 Proportion 
                 Intensity 
                 Deviation 
                 Proportion 
                 Intensity 
                 Deviation 
                 Proportion 
               
               
                   
                 [mcd/m2] 
                 [mcd/m2] 
                 [%] 
                 [mcd/m2] 
                 [mcd/m2] 
                 [%] 
                 [mcd/m2] 
                 [mcd/m2] 
                 [%] 
               
               
                   
               
               
                 Measured 
                 218 
                   
                   
                 243 
                   
                   
                 283 
               
               
                 intensity 
               
               
                 Predicted 
                 210.7 
                 −7.3 
                 −3.3 
                 232.4 
                 −10.6 
                 −4.4 
                 285 
                 2.0 
                 0.7 
               
               
                 intensity 1 
               
               
                 Predicted 
                 212.1 
                 −5.9 
                 −2.7 
                 234.5 
                 −8.5 
                 −3.5 
                 286.4 
                 3.4 
                 1.2 
               
               
                 intensity 2 
               
               
                 Predicted 
                 212.6 
                 −5.4 
                 −2.5 
                 235.9 
                 −7.1 
                 −2.9 
                 285.5 
                 2.5 
                 0.9 
               
               
                 intensity 3 
               
               
                 Predicted 
                 214.9 
                 −3.1 
                 −1.4 
                 237.7 
                 −5.3 
                 −2.2 
                 287.1 
                 4.1 
                 1.4 
               
               
                 intensity 4 
               
               
                 Predicted 
                 214 
                 −4.0 
                 −1.8 
                 240.4 
                 −2.6 
                 −1.1 
                 285.5 
                 2.5 
                 0.9 
               
               
                 intensity 5 
               
               
                 Predicted 
                 217 
                 −1.0 
                 −0.5 
                 240.7 
                 −2.3 
                 −0.9 
                 288.1 
                 5.1 
                 1.8 
               
               
                 intensity 6 
               
               
                   
               
               
                   Deviation [mcd/m2]: Deviation between predicted intensity and measured intensity after 20 min. from light interception    
               
               
                   Proportion[%]: Proportion of predicted intensity to measured intensity after 20 min. from light interception    
               
               
                   Measured intensity: Afterglow intensity actually measured after 20 min. from light interception    
               
               
                   Predicted intensity 1: Predicted intensity calculated based on data measured from 2 to 3 min.    
               
               
                   Predicted intensity 2: Predicted intensity calculated based on data measured from 2 to 3.5 min.    
               
               
                   Predicted intensity 3: Predicted intensity calculated based on data measured from 2 to 4 min.    
               
               
                   Predicted intensity 4: Predicted intensity calculated based on data measured from 2 to 5 min.    
               
               
                   Predicted intensity 5: Predicted intensity calculated based on data measured from 3 to 4 min.    
               
               
                   Predicted intensity 6: Predicted intensity calculated based on data measured from 3 to 5 min.    
               
               
                   The Predicted intensity was calculated using data measured for every 30 sec.    
               
               
                   1. Afterglow intensity test for light-energy storing type pilot sign: illuminance 200 lx for 20 min.    
               
               
                   2. Illuminance in underground passage: 200 lx and more (under an ordinance of Tokyo Fire Defense Agency)    
               
             
          
         
       
     
         [0040]    
       
         
               
             
               
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
             
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 6 
               
               
                   
               
               
                   
               
               
                 Influence of sampling time of measured data to be used to predicted intensity after 20 min. 
               
               
                 from light interception, calculated using the reciprocal of measured intensity 
               
               
                 Case: Resin sample A-1 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Sampling time 
               
             
          
           
               
                   
                 Every 30 sec. 
                 Every 15 sec. 
                 Every 10 sec. 
               
             
          
           
               
                   
                 Intensity 
                 Deviation 
                 Proportion 
                 Intensity 
                 Deviation 
                 Proportion 
                 Intensity 
                 Deviation 
                 Proportion 
               
               
                   
                 [mcd/m2] 
                 [mcd/m2] 
                 [%] 
                 [mcd/m2] 
                 [mcd/m2] 
                 [%] 
                 [mcd/m2] 
                 [mcd/m2] 
                 [%] 
               
               
                   
               
               
                 Measured intensity 
                 243 
                   
                   
                 243 
                   
                   
                 243 
               
               
                 Predicted intensity 1 
                 232.4 
                 −10.6 
                 −4.4 
                 233 
                 −10.0 
                 −4.1 
                 232 
                 −11.0 
                 −4.5 
               
               
                 Predicted intensity 2 
                 235.9 
                 −7.1 
                 −2.9 
                 235.9 
                 −7.1 
                 −2.9 
                 235.7 
                 −7.3 
                 −3.0 
               
               
                 Predicted intensity 3 
                 237.7 
                 −5.3 
                 −2.2 
                 237.7 
                 −5.3 
                 −2.2 
                 237.7 
                 −5.3 
                 −2.2 
               
               
                 Predicted intensity 4 
                 240.4 
                 −2.6 
                 −1.1 
                 240.4 
                 −2.6 
                 −1.1 
                 239.4 
                 −3.6 
                 −1.5 
               
               
                 Predicted intensity 5 
                 240.7 
                 −2.3 
                 −0.9 
                 240.4 
                 −2.6 
                 −1.1 
                 240 
                 −3.0 
                 −1.2 
               
               
                   
               
             
          
           
               
                   
                 Sampling time 
               
             
          
           
               
                   
                 Every 5 sec. 
                 Every 1 sec. 
               
             
          
           
               
                   
                   
                 Intensity 
                 Deviation 
                 Proportion 
                 Intensity 
                 Deviation 
                 Proportion 
               
               
                   
                   
                 [mcd/m2] 
                 [mcd/m2] 
                 [%] 
                 [mcd/m2] 
                 [mcd/m2] 
                 [%] 
               
               
                   
                   
               
               
                   
                 Measured intensity 
                 243 
                   
                   
                 243 
               
               
                   
                 Predicted intensity 1 
                 232.1 
                 −10.9 
                 −4.5 
                 232.2 
                 −10.8 
                 −4.4 
               
               
                   
                 Predicted intensity 2 
                 235.8 
                 −7.2 
                 −3.0 
                 235.7 
                 −7.3 
                 −3.0 
               
               
                   
                 Predicted intensity 3 
                 237.9 
                 −5.1 
                 −2.1 
                 237.5 
                 −5.5 
                 −2.3 
               
               
                   
                 Predicted intensity 4 
                 240.3 
                 −2.7 
                 −1.1 
                 238.8 
                 −4.2 
                 −1.7 
               
               
                   
                 Predicted intensity 5 
                 240.6 
                 −2.4 
                 −1.0 
                 239.6 
                 −3.4 
                 −1.4 
               
               
                   
                   
               
               
                   
                   Deviation [mcd/m2]: Deviation between predicted intensity and measured intensity after 20 min. from light interception    
               
               
                   
                   Proportion[%]: Proportion of predicted intensity to measured intensity after 20 min. from light interception    
               
               
                   
                   Measured intensity: Afterglow intensity actually measured after 20 min. from light interception    
               
               
                   
                   Predicted intensity 1: Predicted intensity calculated based on data measured from 2 to 3 min.    
               
               
                   
                   Predicted intensity 2: Predicted intensity calculated based on data measured from 2 to 4 min.    
               
               
                   
                   Predicted intensity 3: Predicted intensity calcualted based on data measured from 2 to 5 min.    
               
               
                   
                   Predicted intensity 4: Predicted intensity calculated based on data measured from 3 to 4 min.    
               
               
                   
                   Predicted intensity 5: Predicted intensity calcualted based on data measured from 3 to 5 min.    
               
               
                   
                   Light-energy storing condition: illuminance 200 lx for 1 hr.    
               
             
          
         
       
     
         [0041]     Table 6 represents the calculation result of the afterglow intensity for the sample A- 1  at different storing conditions of light energy, which is calculated based on the reciprocal of the afterglow intensity during the specific period until the predetermined time has lapsed from the light interception, in the same way as table 5. In the embodiment, the sampling intervals are 30 seconds, 15 seconds, 10 seconds, 5 seconds, and 1 second. It is obvious that the sampling interval does not affect the accuracy of the measurement.  
         [0042]      FIG. 6  is a graph showing the attenuation of the afterglow intensity at positions P 1  to P 4  on the light storing sign shown in  FIG. 7 . The measured values at those four positions overlap each other and represent a same curve. It is understood that the afterglow intensity does not depend on the measurement position.  
         [0043]      FIG. 8  shows an example of an external view of the stored light intensity measurement device in the embodiment of this invention. The stored light intensity measurement device  101  is used bringing a light measurement unit  102  into intimate contact with the light storing sign  103 . The stored light intensity measurement device  101  is provided with a shaft  104 , a grip  105 , a display unit  106 , and a universal joint  107  in addition to the light measurement unit  102 . The shaft  104  is provided at an end thereof with the grip  105 . A user holds the stored light intensity measurement device  101  with the grip  105 . The display unit  106  is disposed on an upper surface of the grip  105 . The display unit  106  is provided with an indicator like the liquid crystal display, and displays the afterglow intensity of the light storing sign  103 . Another end of the shaft  104  is provided with the universal joint  107 . The universal joint  107  has a ball joint, and determines the position of the light measurement unit  102  at various angles, as well as connects the light measurement unit  102  with the shaft  104 .  
         [0044]     The storing light sign shown in  FIG. 8  illustrates the light storing unit  103  in  FIG. 7  more schematically, and has the colored section  108  and the light storing section  109  likewise. In this case, the arrow for the evacuation is the colored section  108 , and the other area is the light storing section  109 . When the light storing sign  103  is illuminated by an external light, the arrow can be recognized visibly by the colored section  108 . When the environment surrounding the light storing sign  103  is dark, the arrow can be recognized by the afterglow of the light storing section  109 . In  FIG. 8 , the light storing sign  103  is placed on a wall  110 . The light storing sign  103  is at a position on which the wall  110  is adjacent to a wall  111  and a floor  112 .  
         [0045]     When the afterglow intensity of the light storing sign  103  is measured by the stored light intensity measurement device  101 , the user supports the stored light intensity measurement device  101  by holding the grip  105 , and presses the light measurement unit  102  against the light storing section  109  of the light storing sign  103 . The light measurement unit  102  is brought into intimate contact with the light storing section  109 , so that it is possible to shield a light measuring area from outside obstructive light, and this makes it possible to measure the afterglow of the light measuring area. Since the stored light intensity measurement device  101  is provided with the shaft  104  and the universal joint  107 , even if the light storing sign  103  is disposed on the above-mentioned place, the user can perform the measurement without undue stress. Accordingly, the user can fix the light measurement unit  102  at ease for the time necessary to measure the afterglow intensity of the light storing sign  103 . The display unit  106  is disposed on the grip  105 , so that it easy for the user to recognize the afterglow intensity of the light storing sign  103 .  
         [0046]      FIG. 9  is an enlarged view of an example of the external view of the light measurement unit. The light measurement unit  102  is provided with a light intercepting part  201  and a light receiving part  202  on an intimate contacting surface to the light storing sign. The light intercepting part  201  uses a rubber elastic body. By pressing the light measurement unit  102  onto the light storing sign, the rubber elastic body is transformed, so that the light-tightness between the light intercepting part  201  and the light storing sign can be ensured. In this embodiment, the light intercepting part  201  forms the intimate contacting surface in torus form. The light receiving part  202  is disposed at a center of the contacting surface. The light receiving part  202  receives afterglow from the light storing sign. When the light intercepting part  201  is contacted light-tightly with the light storing sign, the light from the outside of the light intercepting part  201  is intercepted completely, so that the outside light does not reach on a measurement area of the light storing sign that is facing to the light receiving part  202 . And the light intercepting part  201  intercepts the afterglow from the corresponding torus area on the light storing sign that contacts with the light intercepting part  201 . Since the obstructive light interfering with the afterglow intensity measurement is intercepted by the light receiving part  202 , the light receiving part  202  can receive the afterglow emitted from only the area corresponding to the part  202 . By using the rubber elastic body, it is easy for the user to keep the light interception.  
         [0047]      FIG. 10  is a sectional view of an example of the light measurement unit. The light measurement unit  102  is provided with an approaching surface  301  that is smaller than the light storing section  109  of the light storing sign  103 . When there is an obstruction around the light storing sign, the light measurement unit  102  cannot contact the light storing sign  103  due to the obstruction. In order to avoid such situation as far as possible, the approaching surface  301  is configured to be smaller than the light storing section  109  of the light storing sign  103 . For instance, when the light storing sign  103  is placed on the riser of stairs, if the approaching surface  301  is larger than the light storing section, the light measurement unit is interfered with a step. In the place as shown in  FIG. 8 , the light measurement unit  102  is interfered with another wall or a floor. In order to measure the afterglow intensity of the light storing sign even in such place, the approaching surface  301  is formed in smaller than the light storing section  109  of the light storing sign  103 . Since the whole surface of the light storing sign  103  is processed so as to get the uniform afterglow intensity, there is no problem even if the afterglow intensity is measured only on a part of the light storing section  109  of the light storing sign  103 .  
         [0048]     The light intercepting part  201  and the light receiving part  202  are placed on the contacting surface of the light measurement unit  102 . In  FIG. 10 , the structure of the light intercepting part  201  is a little different from that in  FIG. 9 . In  FIG. 10 , a torus rubber elastic body  302  is provided to the approaching surface  301 . The intimate contacting surface of the elastic body  302  projects from the approaching surface  301  slightly. According to such structure, when the light measurement unit  102  is pressed against the light storing sign  103 , the elastic body  302  is transformed sufficiently, and it is possible to ensure the tightness between the light measurement unit  102  and the light storing sign  103  properly. Like an example shown in  FIG. 9 , the light receiving part  202  is provided at the center of the elastic body  302 .  
         [0049]     The light receiving part  202  is provided with an opening hole  303 , and a guard window  304  is slightly deep inside the opening hole  303 . And there is a light receiving element  305  at a bottom of the opening hole  303 . The light receiving element  305  can use a photoelectric conversion element like a photodiode, and generates electric signals according to the incident light through the guard window  304 . The output of the light receiving element  305  is given to a substrate  306 . The substrate  306  generates digital data according to the analog electric signals from the light receiving element  305 , and outputs the data to a signal line  307 . The signal line  307  is installed in the universal joint  107  and the shaft  104 , and connected to a signal processing unit in the grip. The digital data of the measurement result is transferred from the substrate  306  to the signal processing unit through the signal line  307 .  
         [0050]      FIG. 11  is a diagram for schematically explaining an example of an electric structure of the stored light intensity measurement device. The light receiving element  305  receives the light from the light storing sign, and then outputs the analog electric signal to the substrate  306  according to the received light. The substrate  306  is provided with an analog processing unit  401 , AD converter  402 , and the like. The analog processing unit  401  amplifies the inputted analog electric signals, and performs the sampling-and-holding of the signals. The AD converter  402  converts the electric signals held for every sampling period to the digital data.  
         [0051]     The output of the substrate  306  is connected to the signal processing unit  403 . The signal processing unit  403  can use a special-purpose circuit or a general-purpose circuit. In this embodiment, the general-purpose circuit is used to the signal processing unit  403 . The signal processing unit  403  is provided with a bus  404 . The bus  404  is connected to an interface circuit  405  for the substrate  306 . The signal processing unit  403  receives the digital data from the substrate  306  through the interface circuit  405 . The bus  404  is connected to RAM  406 , ROM  407 , and CPU  408  as well as the interface circuit  405 . RAM  406  can store the digital data received from the substrate  306 . ROM  407  stores programs and setting data for the signal processing and the control. CPU  408  performs the calculation for the signal processing and the control according to instructions of the program. CPU  408  calculates the afterglow intensity of the light storing sign when a predetermined time lapsed after the measurement start, based on the data read from RAM  406 .  
         [0052]     The bus  404  is also connected to the interface circuit  409  for the display unit  106 . The signal processing unit  403  in this embodiment controls the display unit  106  through the interface circuit  409 . The display unit  106  is provided with operation buttons  411  and  412  in addition to an indictor  410  for displaying the measurement result. For instance, the operation button  411  is a menu selecting button, and the operation button  412  is an enter button. A user selects a menu item by the operation button  411 , and then ensures the selection by the operation button  412 . The menu items are an initialization, a calibration, and an execution of measurement. The calibration is for a case of measuring a reference plate of which afterglow intensity is known. When the user selects the execution of measurement and operates to enter the selection, the signal processing unit  403  fetches the digital data representing the measurement result into RAM  406 . The digital data is sequentially stored in RAM  406  for every sampling period. After CPU  408  obtains necessary samples, it calculates the afterglow intensity of the light storing sign according to the sample values.  
         [0053]      FIG. 12  is a functional block diagram when CPU  408  works together with the program stored in ROM  407 . The data from the light receiving element  305  is sampled at specific intervals, and then converted to the digital data by the AD converter  402 . The obtained digital data is stored in RAM  406  or a different storage means through the interface circuit  405 .  
         [0054]     A first calculation unit  511  finds the straight line (the linear approximate equation) corresponding to reciprocals of the afterglow intensity by means of the data between a first time and a second time after the specific time lapsed from the light interception, out of the sampling data being stored in RAM  406 . That is to say, after the constants α and β of the equation (2) are found, the values are stored at a specific location of RAM  406 . Then, a second calculation unit  512  calculates the afterglow intensity after the specific time t according to the above equation (2). It is obvious from Table 3 that the first time should be two or three minutes, and it is enough that the second time should be one or two minutes from the first time. In addition, the afterglow intensity to be calculated is the intensity after 20 minutes lapsed from the light interception. A display means  413  is also configured to calculate the afterglow intensity, and then display the calculated result on the indicator  410 .  
         [0055]     Therefore, the invention can measure the afterglow intensity of the light storing sign in a short time, and it can be used very effectively for the maintenance and investigation of the light storing sign.