JPH07140003A - Measurement device for visibility degree - Google Patents

Abstract

PURPOSE:To measure a visibility degree in a condition of existence of smoke in a tunnel or in fog. CONSTITUTION:A background luminance-measuring section 1 measures background luminance of an object and an object luminance-calculating section 2 calculates luminance of the object from the background luminance. An optical screen luminance-measuring section 3 measures luminance of an optical screen that is generated between the object and an observer and a penetration rate-measuring section 4 measures a penetration rate of a light. A background apparent luminance-calculating section 5 calculates apparent luminance of a background from the background luminance, luminance of the optical screen and penetration rate and an object apparent luminance-calculating section 6 calculates apparent luminance of the object from the luminance of the object, luminance of the optical screen and penetration rate. A luminance difference-calculating section 7 calculates a luminance difference DELTAL of the apparent luminance. An equivalent optical screen luminance-measuring section 9 measures equivalent optical screen luminance in terms of an eye of the observer and a central hole adaptation luminance-measuring section 8 measures central hole luminance in terms of the eye. A luminance difference distinction threshold-calculating section 10 calculates a luminance difference distinction threshold DELTALmin in terms of the eye of the observer from the above luminance. A visibility degree-calculating section 11 calculates a visibility degree from the luminance difference DELTAL and luminance difference distinction threshold DELTALmin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a visibility measuring device.

[0002]

2. Description of the Related Art A conventional visibility measuring apparatus provides a light curtain between an object and an observer's eye and keeps the background brightness of the object constant so that the object cannot be seen. I was looking for visibility at that time. Since this visibility measuring device cannot reproduce the effect of the equivalent light curtain brightness generated by the light incident on the eye from the peripheral visual field, a visibility measuring device which has improved this point was devised (Japanese Patent Laid-Open No. 62-22724, etc.). ).

The structure of this visibility measuring apparatus is shown in FIG.
This visibility measuring apparatus obtains the brightness of the object and its background by the brightness distribution measuring unit 21 and the object condition setting unit 20,
The brightness difference calculation unit 22 calculates the brightness difference ΔL between the object and the background. On the other hand, based on the equivalent light curtain brightness and the fovea adaptation brightness of the observer's eyes obtained by the equivalent light curtain brightness measurement unit 23 and the fovea adaptation brightness measurement unit 24, the brightness difference discrimination threshold calculation unit 25 calculates the The brightness difference valve threshold ΔLmin of the eye is calculated, and the visibility calculation unit 26
Calculates the visibility VL from the luminance difference ΔL and the luminance difference discrimination threshold ΔLmin by the following equation: VL = ΔL / ΔLmin (1) With this configuration, the visibility of the object can be measured.

[0004]

As described above, in measuring the visibility, it is necessary to obtain the brightness difference between the object and the background of the object. However, when there is soot in the road tunnel or in fog, etc. Under the condition, the brightness of the object and the background seen by the observer is different from that when there is no soot or fog. That is, the effect of reducing the light transmittance due to soot or mist to reduce the brightness and the effect of increasing the brightness by irradiating the soot or mist with illumination light to generate a light curtain. When measuring visibility in a road tunnel or in fog, it is necessary to consider the effects of light transmittance and curtain brightness, but with conventional visibility measuring devices, the effects of transmittance and curtain brightness are considered. Could not be reproduced.

Further, among the elements necessary for measuring the visibility, the equivalent light curtain brightness quantitatively expresses the influence of intraocular scattering that occurs when light enters the observer's eye. In order to measure this equivalent light curtain brightness, a very complicated integral calculation is performed based on the result of the brightness measurement, or a special optical lens called a glare lens is obtained and attached to the brightness meter. It had to be used and prevented the easy construction of the elements of the visibility measuring device.

[0006]

In order to solve the above problems, the visibility measuring apparatus of the present invention comprises a background brightness measuring unit for measuring the brightness of the background at a position where an object is assumed to exist, the observer, and the background. A light curtain brightness measuring unit that measures the brightness of a light curtain existing between the object and a transmittance measuring unit that measures the light transmittance between the observer and the object, and the background brightness measurement. Section, the light curtain luminance measuring section and the transmittance measuring section, and a background apparent luminance calculating section for calculating the apparent luminance of the background seen by the observer by inputting signals from the observer and a signal from the background luminance measuring section. An object viewed from an observer by inputting signals from the object brightness calculating section for calculating the brightness of the object by inputting the signal, the object brightness calculating section, the curtain curtain brightness measuring section and the transmittance measuring section. An object apparent brightness calculation unit that calculates the apparent brightness of the A brightness difference calculation unit that inputs a signal from the apparent brightness calculation unit and the object apparent brightness calculation unit and calculates a brightness difference between the object and the background seen by the observer, and the observer's eye. Equivalent light curtain brightness measuring unit for measuring the equivalent light curtain brightness, fovea centralis adaptation brightness measuring unit for measuring the brightness to which the fovea of the eye of the observer adapts, the equivalent light curtain brightness measuring unit and the center A signal from the fossa adaptation luminance measurement unit is input to input a signal from the luminance difference discrimination threshold calculation unit that calculates the luminance difference discrimination threshold of the observer's eye, and the luminance calculation unit and the luminance difference discrimination threshold calculation unit. And a visibility calculation unit that calculates the visibility of the object.

Further, the fovea adaptation luminance measuring section is omitted, and the luminance difference discrimination threshold calculating section inputs the signals from the background apparent luminance calculating section and the equivalent light curtain luminance measuring section to calculate the luminance difference discriminating threshold. Is.

Further, instead of the background luminance measuring section, an illuminance measuring section for measuring illuminance at a position where an object is assumed to exist, and a background luminance for calculating a background luminance by inputting a signal from the illuminance measuring section. And a calculation unit.

Further, in place of the equivalent light curtain luminance measuring section, an equivalent light curtain luminance calculating section for inputting a signal from the illuminance measuring section and calculating the equivalent light curtain luminance as seen by an observer is provided.
In addition, a background apparent brightness measurement unit that measures the apparent brightness when the background of the position where the object is assumed to be present is viewed from the observer, and a light curtain existing between the observer and the object. A light curtain brightness measuring section for measuring brightness, a transmittance measuring section for measuring light transmittance between the observer and the object, the background apparent brightness measuring section, the light curtain brightness measuring section and the An object apparent brightness calculation unit that inputs a signal from the transmittance measurement unit and calculates the apparent brightness of the object viewed from the observer, the background apparent brightness measurement unit, and the object apparent brightness calculation unit. A luminance difference calculation unit for calculating a luminance difference between the object and the background viewed from the observer by inputting a signal from the observer, and an equivalent light curtain luminance measurement unit for measuring an equivalent light curtain luminance of the observer's eye. , The equivalent light curtain luminance measuring section and the background apparent luminance measuring section A luminance difference discrimination threshold calculation unit for calculating a luminance difference discrimination threshold of the observer's eye by inputting a signal from the object, and inputting a signal from the luminance difference calculation unit and the luminance difference discrimination threshold calculation unit And a visibility calculation unit that calculates visibility.

Further, instead of the equivalent light curtain brightness measuring section, an illuminance measuring section for measuring the illuminance at a position where an object is assumed to exist, and a signal from the illuminance measuring section are input and viewed by an observer. And an equivalent light curtain brightness calculation unit for calculating the equivalent light curtain brightness.

Further, instead of the light curtain brightness measuring section, the light curtain brightness for calculating the brightness of the light curtain existing between the observer and the object by inputting signals from the transmittance measuring section and the illuminance measuring section. It is provided with a calculation unit.

[0012]

The visibility measuring apparatus of the present invention includes, in addition to the conventional visibility measuring apparatus, a light curtain brightness measuring section for measuring the brightness of a light curtain generated between an object and an observer. By providing a transmittance measurement unit that measures the transmittance of light between an object and an observer, the measurement results of the curtain curtain brightness measurement unit and the transmittance measurement unit are used to calculate visibility, and Therefore, visibility can be measured even in the presence of soot and in fog.

Further, instead of the equivalent light curtain brightness measuring section, an illuminance measuring section for measuring the illuminance and an equivalent light curtain brightness calculating section for calculating the equivalent light curtain brightness from the measurement result of the illuminance measuring section are provided. It is possible to easily measure the light curtain brightness and simplify the configuration of the visibility measuring device.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of a visibility measuring apparatus according to a first embodiment of the present invention. In FIG. 1, the background luminance measuring unit 1 measures the luminance of the background at a position where an object is assumed to exist. The object brightness calculation unit 2 calculates the object brightness Lo (candelas per square meter) from the background brightness Lb (candelas per square meter) and the brightness contrast C (%) measured by the background brightness measurement unit 1 as Lo = Lb × ( 1-C / 100) ... (2).

Here, it is "assumed that an object exists".
Is, for example, a case where it is assumed that there is an obstacle on the road surface that obstructs the operation of the vehicle.
If there are obstacles on the road, the obstacles may interfere with the operation of the vehicle and lead to an accident. Therefore, it is important to measure the visibility for the purpose of checking whether the driver can find obstacles on the road. However, under normal conditions, there are no obstacles on the road surface. Therefore, it is assumed that an object having a certain brightness contrast to the road surface exists on the road surface, and the visibility of this object is obtained. In this case, the luminance contrast C in the expression (2) is considered to be 20 to 60%.

When the distance between the object assumed to be present and the observer is A (m), the light curtain brightness measuring unit 3
The luminance Lv of the light curtain generated during the distance A (for example, 100 m) is measured. On the other hand, the transmittance measuring unit 4 measures the transmittance τ (%) of light during the distance A. The effect that the apparent brightness of the object and the background of the object seen by the observer becomes smaller than the actual brightness because the light transmittance decreases in the presence of soot in the road tunnel or in the fog. Works. On the other hand, the light curtain generated by soot or fog is superimposed on the object brightness and the background brightness, and the effect of increasing the apparent brightness of the object and the background is exerted.

The background apparent brightness calculation unit 5 transmits the background brightness Lb (candelas per square meter) measured by the background brightness measurement unit 1, the light curtain brightness Lv (candelas per square meter) measured by the light curtain brightness measurement unit 3, and the transmission. From the transmittance τ (%) measured by the rate measuring unit 4, the apparent brightness Lb ′ (candelas per square meter) of the background is calculated by Lb ′ = Lb × τ / 100 + Lv (3).

The object apparent brightness calculation unit 6 calculates the object brightness Lo (candelas per square meter) calculated by the object brightness calculation unit 2 and the light curtain brightness L measured by the light curtain brightness measurement unit 3.
From v (candelas per square meter) and the transmittance τ (%) measured by the transmittance measuring unit 4, the apparent brightness L of the object
o ′ (candelas per square meter) is calculated by Lo ′ = Lo × τ / 100 + Lv (4).

The brightness difference calculation unit 7 calculates the background apparent brightness Lb 'calculated by the background apparent brightness calculation unit 5 and the apparent brightness L of the object calculated by the object apparent brightness calculation unit 6.
o ′ is input, and the brightness difference ΔL (square meter per candela) is calculated by ΔL = | Lo′−Lb ′ | (5) and output to the visibility calculation unit 11.

The equivalent light curtain brightness measurement unit 9 measures the equivalent light curtain brightness Leq of the observer's eye when looking at the object.
The equivalent light curtain luminance Leq can be measured by mounting a special optical lens called a glare lens on a luminance meter.
The fovea adaptation luminance measuring unit 8 adjusts the fovea adaptation luminance Laf to which the fovea of the eye of the observer when looking at the object adapts.
To measure.

The brightness difference discrimination threshold calculation unit 10 uses the equivalent light curtain brightness Leq measured by the equivalent light curtain brightness measurement unit 9 and the fovea adaptation brightness Laf measured by the fovea adaptation brightness measurement unit 8 to observer's eyes. The brightness difference discrimination threshold ΔLmin is calculated and output to the visibility calculator 11. Here, the brightness discrimination threshold ΔLmin
Is a brightness difference discrimination threshold ΔL corresponding to the foveal adaptation brightness Laf
ΔLmin = ΔLmin (1) as the sum of min (1) (candelas per square meter) and the brightness difference discrimination threshold ΔLmin (2) (candelas per square meter) corresponding to both the fovea adaptation brightness Laf and the equivalent light curtain brightness Leq. It is calculated by + ΔLmin (2) ... (6). The luminance difference discrimination threshold ΔLmin (1) and the luminance difference discrimination threshold ΔLmin (2) are the fovea adaptation luminance Laf and the fovea adaptation luminance Laf and the equivalent light curtain luminance L.
Corresponding to the sum of eq, it can be obtained according to the relationships of FIG. 7 and FIG. 8, respectively.

The visibility calculation unit 11 calculates the luminance difference ΔL (candelas per square meter) calculated by the luminance difference calculation unit 7 and the luminance difference discrimination threshold ΔLmi calculated by the luminance difference discrimination threshold calculation unit 10.
The visibility VL is calculated from n (candelas per square meter) by the formula (1), and the measurement result of the visibility VL is displayed.

With the above configuration, the visibility measuring device is capable of measuring the visibility even when soot is present in the road tunnel or when it is necessary to consider the influence of the light transmittance and the curtain brightness in the fog. Can be configured.

In a situation where the observer is always gazing at the road surface in front, such as when measuring the visibility of a driver who is driving a car, it is assumed that the object is present in the fovea of the observer. On the road surface, that is, the apparent brightness of the background seen by the observer,
af can be regarded as equal to the apparent brightness Lb ′ of the background. Therefore, in the case of measuring the visibility during driving of a vehicle, as in the second embodiment shown in FIG. 2, the fovea adaptation luminance measuring unit 8 of the constituent elements of the first embodiment is omitted and the luminance difference discrimination is performed. The threshold calculation unit 10 inputs a signal from the apparent brightness Lb ′ of the background calculated by the background apparent brightness calculation unit 5 and the equivalent light curtain brightness Leq measured by the equivalent light curtain brightness measurement unit 9 to perform brightness difference discrimination. The threshold ΔLmin can be calculated, and the same effect as that of the first embodiment can be obtained in this structure as well.

Further, when measuring the visibility of a driver who is driving an automobile, when the material of the background part of the object is constant and the reflection characteristic can be approximated to a perfect diffusing surface. Can obtain the background brightness from the illuminance at that position. Therefore, as in the third embodiment shown in FIG. 3, instead of the background luminance measuring unit 1 of the constituent elements of the first embodiment, an illuminance measuring unit 12 that measures the illuminance of the background portion and an illuminance measuring unit 12 are used. Even if the background luminance calculation unit 13 that inputs the measured illuminance E to calculate the background luminance is provided, the same effect as that of the first embodiment can be obtained, and the illuminance that is easier to handle than the luminance meter. In total, some of the elements can be composed. When the background of the object is the road surface, the illuminance and the brightness of the road surface are in a proportional relationship, and this constant of proportionality is called an average illuminance conversion coefficient. Background luminance L from the average illuminance conversion coefficient K (each lux to each candela and parallel meter) and the illuminance E (lux)
b (candelas per square meter) can be calculated by Lb = E / K (7). According to the literature (Foundation Highway Study Group: Tunnel Lighting Design Guidelines, 1990),
The average illuminance conversion coefficient K is 13 (lux per candela per square meter) for a general concrete road surface and 18 (lux per candela per square meter) for a general road surface material. The background luminance calculation unit 13 calculates the background luminance based on the equation (7).

When the equivalent light curtain brightness of the observer's eyes is proportional to the illumination level, such as inside a road tunnel, as in the case of the third embodiment shown in FIG. In place of the equivalent light curtain brightness measurement unit 9, by providing the equivalent light curtain brightness calculation unit 16 that calculates the equivalent light curtain brightness of the observer's eye based on the illuminance measurement result measured by the illuminance measurement unit 12, The same effect as that of the first embodiment can be obtained. Fig. 9 shows the results obtained by experiment for the effect of light transmittance on the equivalent light curtain brightness of the observer's eye in the presence of soot in the tunnel.
Shown in. From this result, it is understood that the equivalent light curtain brightness is hardly affected by the light transmittance and the light curtain brightness and can be calculated as being proportional to the illumination level, that is, the illuminance on the road surface. Therefore, the equivalent light curtain brightness can be calculated based on the illuminance measurement result, and a part of the elements can be configured with an illuminance meter that is easier to handle than a brightness meter.

When the properties of soot and smoke generated in the tunnel are constant inside the road tunnel, the light curtain brightness measuring unit 3 of the first embodiment is used as in the third embodiment shown in FIG.
Instead of, the illuminance E measured by the illuminance measuring unit 12, the light transmittance τ (%) measured by the transmittance measuring unit 4, and the distance A (m) between the observer and the object The configuration may include the light curtain brightness calculation unit 17 that calculates Lv.
FIG. 10 shows an example of the result of measurement of the relationship between the light transmittance per distance A (m) and Lv with the illuminance E being constant. The light curtain brightness calculation unit 17 multiplies the light curtain brightness per unit illuminance obtained from the relationship between the transmittance and the light curtain brightness shown in FIG. 10 by the measured illuminance to calculate the necessary light curtain brightness Lv. In addition, in FIG. 10, although the distance 100 m is not measured,
It is understandable that similar measurement results can be obtained.

As described above, with the configuration of the third embodiment shown in FIG. 3, only two components, the illuminance measuring section 12 and the transmittance measuring section 4, can actually measure the physical quantity. The other components can be configured to be program-processed using, for example, a computer, and the overall configuration is simplified.

Next, a fourth embodiment of the present invention will be described with reference to the drawings. In FIG. 4, the background apparent luminance measuring unit 1
4 measures the apparent brightness of the background at the position where the object is assumed to be present. The light curtain brightness measurement unit 3 measures the brightness L of the light curtain during a distance A (m) generated between the object and the observer.
Measure v. On the other hand, the transmittance measuring unit 4 measures the transmittance τ (%) of light during the distance A. The object apparent brightness calculation unit 15 includes the light curtain brightness Lv (candelas per square meter) measured by the light curtain brightness measurement unit 3, the transmittance τ (%) measured by the transmittance measurement unit 4, and the background apparent brightness measurement unit. 1
From the apparent luminance Lb '(candelas per square meter) of the background measured in No. 4, the apparent luminance L of the object
o '(candelas per square meter)

[0030]

It is calculated by The brightness difference calculation unit 7 determines the object and the object from the apparent brightness Lb ′ of the background measured by the background apparent brightness measurement unit 14 and the apparent brightness Lo ′ of the object calculated by the object apparent brightness calculation unit 15. The apparent brightness difference ΔL of the background is calculated. The equivalent light curtain brightness measurement unit 9
The equivalent light curtain luminance Leq of the observer's eye is measured. The brightness difference discrimination threshold calculation unit 10 calculates, from the apparent brightness Lb ′ of the background measured by the background apparent brightness measurement unit 14 and the equivalent light curtain brightness Leq of the observer's eye measured by the equivalent light curtain brightness measurement unit, According to FIGS. 7 and 8, the luminance difference discrimination threshold ΔLm of the observer's eye
Calculate in. Here, the fovea adaptation luminance L of FIG. 7 and FIG.
af can be regarded as equal to the apparent luminance Lb ′ of the background. The visibility calculation unit 11 includes the brightness difference calculation unit 7
The visibility VL is obtained from the brightness difference ΔL calculated in step S1 and the brightness difference discrimination threshold ΔLmin calculated by the brightness difference discrimination threshold value calculator 10 according to the equation (1).

With the above-mentioned structure, as in the first embodiment, the visibility is measured in the presence of soot in the tunnel or in the fog where the brightness of the curtain and the light transmittance affect the visibility. can do. The difference from the first embodiment is that
The apparent brightness Lb 'of the background is directly measured by the background apparent brightness measuring unit, and the apparent brightness Lo' of the object is obtained from the measurement result Lb ', the light curtain brightness Lv, and the light transmittance τ. .

As in the fifth embodiment shown in FIG. 5,
Among the constituent elements of the fourth embodiment, the equivalent light curtain luminance measuring unit 9
Instead of, the illuminance measuring unit 12 and the equivalent light curtain luminance calculating unit 16 that calculates the equivalent light curtain luminance Leq from the illuminance E measured by the illuminance measuring unit 12 can provide the same effect. Further, instead of the light curtain brightness measuring unit 3, a light curtain brightness Lv is calculated from the illuminance E measured by the illuminance measuring unit 12 and the light transmittance τ measured by the transmittance measuring unit 4. Even if the portion 17 is provided, the same effect can be obtained.

[0034]

As described above, according to the present invention, by measuring the brightness of light curtain and the transmittance of light and using them for the calculation of the visibility, the presence of soot in a road tunnel, the fog, etc. It is possible to measure the visibility even under the condition of.

Further, instead of the equivalent light curtain luminance measuring section, an illuminance measuring section for measuring illuminance and an equivalent light curtain luminance calculating section for calculating the equivalent light curtain luminance from the measurement result of the illuminance measuring section are provided, so that the equivalent light curtain luminance is calculated. It is possible to easily measure the brightness of the light curtain and to simplify the configuration of the visibility measuring device.

Further, in place of the light curtain brightness measuring section which is complicated to measure, a light curtain brightness calculating section for calculating the light curtain brightness from the measurement results of the transmittance measuring section and the illuminance measuring section is provided to measure the visibility. The configuration of the measuring instrument of the device can be simplified.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of a visibility measuring device of the present invention.

FIG. 2 is a configuration diagram of a second embodiment of the visibility measuring device of the present invention.

FIG. 3 is a configuration diagram of a third embodiment of the visibility measuring device of the present invention.

FIG. 4 is a configuration diagram of a visibility measuring device according to a fourth embodiment of the present invention.

FIG. 5 is a configuration diagram of a visibility measuring device according to a fifth embodiment of the present invention.

FIG. 6 is a block diagram of a conventional visibility measuring device.

FIG. 7: Foveal adaptation luminance and luminance difference discrimination threshold ΔLmin
Relationship diagram with (1)

FIG. 8 is a relational diagram of the sum of equivalent screen curtain brightness and fovea adaptation brightness and the brightness difference discrimination threshold ΔLmin (2).

FIG. 9 is a diagram showing the relationship between light transmittance and equivalent light curtain brightness.

[Figure 10] Relationship between light transmittance and curtain brightness

[Explanation of symbols]

 1 Background Luminance Measurement Unit 2 Object Luminance Calculation Unit 3 Light Curtain Luminance Measurement Unit 4 Transmittance Measurement Unit 5 Background Apparent Luminance Calculation Unit 6 Object Apparent Luminance Calculation Unit 7 Luminance Difference Calculator 8 Foveal Adaptation Luminance Measurement Unit 9 Equivalent Light Curtain luminance measurement unit 10 Luminance difference discrimination threshold calculation unit 11 Visibility calculation unit 12 Illuminance measurement unit 13 Background luminance calculation unit 14 Background apparent luminance measurement unit 15 Object apparent luminance calculation unit 16 Equivalent luminous curtain luminance calculation unit 17 Light curtain luminance calculation Department

Claims (7)

[Claims] 1. A background brightness measuring unit for measuring the brightness of the background at a position where an object is assumed to exist, and a light curtain brightness measurement for measuring the brightness of a light curtain existing between an observer and the object. Section, a transmittance measuring section for measuring the transmittance of light between the observer and the object, a signal from the background luminance measuring section, the curtain curtain luminance measuring section and the transmittance measuring section. A background apparent brightness calculation unit that calculates the apparent brightness of the background that is input from the observer, an object brightness calculation unit that inputs the signal from the background brightness measurement unit and calculates the brightness of the object, and the target Object apparent brightness calculation unit that inputs signals from the object brightness calculation unit, the curtain curtain brightness measurement unit, and the transmittance measurement unit, and calculates the apparent brightness of the object viewed by the observer, and the background apparent brightness Input signals from the calculation unit and the object apparent brightness calculation unit. A brightness difference calculation unit that calculates a brightness difference between the object and the background viewed from the observer, an equivalent light curtain brightness measurement unit that measures an equivalent light curtain brightness of the observer's eye, and the observer's The fovea adaptation luminance measuring unit for measuring the luminance to which the fovea of the eye adapts, and the luminance difference between the eyes of the observer by inputting signals from the equivalent light curtain luminance measuring unit and the fovea adaptation luminance measuring unit. A brightness difference discrimination threshold calculation unit that calculates a discrimination threshold, and a visibility calculation unit that inputs a signal from the brightness difference calculation unit and the brightness difference discrimination threshold calculation unit and calculates the visibility of the object are provided. Visibility measuring device characterized by. 2. The fovea adaptation luminance measuring section is omitted, and the luminance difference discrimination threshold calculating section inputs signals from the background apparent luminance calculating section and the equivalent curtain curtain luminance measuring section to calculate the luminance difference discriminating threshold. The visibility measuring device according to claim 1, wherein: 3. An illuminance measuring unit for measuring illuminance at a position where an object is assumed to exist instead of the background luminance measuring unit, and a background luminance for calculating a background luminance by inputting a signal from the illuminance measuring unit. The visibility measuring apparatus according to claim 1, further comprising a calculating unit. 4. An equivalent light curtain brightness calculation unit for inputting a signal from the illuminance measurement unit and calculating the equivalent light curtain brightness seen by an observer, instead of the equivalent light curtain brightness measurement unit. The visibility measuring device according to claim 3. 5. A background apparent luminance measuring unit for measuring apparent luminance when an observer sees a background at a position where an object is assumed to exist, and exists between the observer and the object. A light curtain brightness measuring unit for measuring the brightness of the light curtain, a transmittance measuring unit for measuring the light transmittance between the observer and the object, the background apparent brightness measuring unit, and the light curtain brightness measuring Section and the transmittance measuring section, and inputs the signals from the object and the object apparent brightness calculating section for calculating the apparent brightness of the object seen by the observer, the background apparent brightness measuring section and the object apparent brightness. A brightness difference calculation unit that inputs a signal from a calculation unit and calculates a brightness difference between the object viewed from the observer and the background, and an equivalent light curtain brightness that measures an equivalent light curtain brightness of the observer's eye. Measuring part, the equivalent light curtain brightness measuring part and the background apparent brightness A luminance difference discrimination threshold calculation unit that inputs a signal from the measurement unit and calculates a luminance difference discrimination threshold of the observer's eye, and inputs a signal from the luminance difference calculation unit and the luminance difference discrimination threshold calculation unit. A visibility measuring device comprising: a visibility calculating unit that calculates the visibility of an object. 6. An illuminance measuring unit that measures illuminance at a position where an object is assumed to exist, instead of the equivalent light curtain luminance measuring unit, and a signal from the illuminance measuring unit is input and viewed by an observer. The visibility measuring device according to claim 5, further comprising: an equivalent light curtain brightness calculation unit that calculates an equivalent light curtain brightness. 7. A light curtain brightness for calculating the brightness of a light curtain existing between an observer and an object by inputting signals from a transmittance measuring section and an illuminance measuring section instead of the light curtain brightness measuring section. 7. The visibility measuring device according to claim 3, further comprising a calculating unit.