As shown in
As shown in
Further, the illuminating main body 4 has an unillustrated output adjusting means for separately adjusting outputs of the respective LEDs 51 to 54 every light source portion. This output adjusting means is constructed by an electronic device such as a microcomputer, etc., and is connected to each of the LEDs 51 to 54. This output adjusting means sets the outputs of the respective LEDs 51 to 54 so as to relatively strengthen the outputs of short wavelength LEDs of green LED 52 and blue LED 53 with respect to the outputs of long wavelength LEDs of red LED 51 and yellow LED 54 in the footway side light source portion 42. Conversely, in the roadway side light source portion 41, the output adjusting means sets the outputs of the respective LEDs 51 to 54 so as to relatively strengthen the outputs of long wavelength LEDs of red LED 51 and yellow LED 54 with respect to the outputs of short wavelength LEDs of green LED 52 and blue LED 53. Namely, the spectral characteristics of light synthesized by the respective LEDs 51 to 54 of the footway side light source portion 42 become rich in blue-green light, and the spectral characteristics of light synthesized by the respective LEDs 51 to 54 of the roadway side light source portion 41 become rich in green-red light by the output adjusting means.
In the first embodiment, the short wavelength LEDs of green LED 52 and blue LED 53 correspond to “a short wavelength color light source for emitting light including at least blue light or green light”, and the long wavelength LEDs of red LED 51 and yellow LED 54 correspond to “a long wavelength color light source for emitting light including at least yellow light or red light”. The output of the white LED may not be adjusted by the output adjusting means.
Concretely, the outputs of the respective LEDs 51 to 54 are adjusted by the above output adjusting means such that a value IP obtained by the following formula (2) in the spectral characteristics of light irradiated from the footway side light source portion 42, i.e., the synthesized light of each of the LEDs 51 to 54 of the footway side light source portion 42 is greater than a value IC obtained by the following formula (2) of the spectral characteristics of light irradiated from the roadway side light source portion 41, i.e., the synthesized light of each of the LEDs 51 to 54 of the roadway side light source portion 41.
In formula (2), S(λ) is spectral radiant intensity of wavelength λ, V(λ) is photopic vision visual spectral sensitivity, and V′(λ) is scotopic vision visual spectral sensitivity.
A wavelength area of blue-green light is mainly set to 430 to 570 nm although there is an individual difference. As an experimental result, it has been found that a driver of an automobile can clearly visualize a pedestrian, etc. on the footway 22 by raising the spectral radiant intensity at particularly, 450 to 550 nm within this wavelength area of the blue-green light. Accordingly, in the above formula (2), the integrating wavelength area of a numerator side is set to 450 to 550 nm.
Here, a visual cell on a retina of a human being is constructed by a cone and a rod. The cone manages a function for discriminating a color under a light situation (photopic vision). The rod manages a function for discriminating light and darkness under a dark situation (scotopic vision). As shown by V within
Further, in an automobile driving environment of nighttime, it corresponds to mesopic vision as an intermediate state of the scotopic vision and the photopic vision. Therefore, it lies under a condition in which the rod is also actively operated as well as the cone.
As shown in
In accordance with the illuminating device 1 of the first embodiment, the footway side light source portion 42 illuminates the footway 22 by light of spectral characteristics high in spectral radiant intensity of a wavelength area of blue-green light, particularly, 450 to 550 nm so that the footway 22 is illuminated by light of spectral characteristics high in spectral radiant intensity near 507 nm as a peak of the visual sensitivity of the rod. Therefore, the driver of the automobile can easily visualize a pedestrian by the rod.
Further, the driver of the automobile can more clearly visualize the pedestrian, etc. on the footway by increasing the above value IP from the above value IC until a degree able to sense a clear difference in brightness by the driver of the automobile. Therefore, an experiment for comparing a sensing way of brightness of a street illuminated by the light source is made by adjusting an output by using the light source of a different kind. As a result, it has been found that the difference (the difference between the above value IP of the footway side light source portion 42 and the above value IC of the roadway side light source portion 41) of value I of the above formula (2) is required by 30 percent or more to be able to sense a luminance difference of 10 percent or more said as a clear difference in brightness in the scotopic vision by a human being.
For the illuminating device arranged in a street, it is required that the luminance of the street irradiated by light is uniform. Therefore, it is necessary to set both the light source portions 41, 42 such that the luminance of the roadway 21 irradiated by the roadway side light source portion 41 and the luminance of the footway 22 irradiated by the footway side light source portion 42 are equal.
As can be seen from
Accordingly, it is preferable to set the above value IP to be greater by 30 percent or more than the above value IC. Thus, the driver of an automobile easily and more clearly visualizes a pedestrian, etc. on the footway 22.
The roadway side light source portion 41 illuminates the roadway 21 by light of spectral characteristics high in spectral radiant intensity of a wavelength area of yellow-red color light. Therefore, the roadway 21 is illuminated by light of spectral characteristics high in spectral radiant intensity near 555 nm as a peak of visual sensitivity of the cone. Therefore, the driver of the automobile can easily visualize another vehicle, etc. on the roadway 21 by the cone.
The illuminating device 1 of the first embodiment irradiates light of spectral characteristics high in spectral radiant intensity in the wavelength area of 450 to 550 nm from an upward direction of the street 2 toward the footway 22. Accordingly, no light irradiated from the footway side light source portion 42 is directly incident to a driver's eye of the automobile running the roadway 21. Therefore, it is possible to avoid a risk that glare is given to the driver of the automobile by the light irradiated from the footway side light source portion 42.
In the first embodiment, both the light source portions 41, 42 are constructed by LEDs 51 to 54 of four colors. Therefore, the spectral characteristics can be adjusted by changing the output of each of the LEDs 51 to 54 of the respective light source portions 41, 42 in conformity with an environment, etc. of an arranging place of the illuminating device 1 by the above output adjusting means. Therefore, light suitable for the environment of the arranging place of the illuminating device 1, etc. can be irradiated to the street 2 without changing the light source.
In the first embodiment, the explanation has been made by using the LEDs 51 to 54 of four colors as the light sources of both the light source portions 41, 42. However, the present invention is not limited to this case. For example, as shown as a second embodiment in
As a third embodiment, a light source of white light of 5800 K in color temperature may be also used as the light source of the footway side light source portion 42, and a light source of white light of 3800 K in color temperature may be also used as the light source of the roadway side light source portion 41.
In the first embodiment, the spectral characteristics of light irradiated from the footway side light source portion 42 are explained so as to adjust the output of each of the LEDs 51 to 54 by the above output adjusting means such that the value IP obtained by the above formula (2) is larger than the value IC obtained by the formula (2) of the spectral characteristics of light irradiated from the roadway side light source portion 41. However, the present invention is not limited to this case. It is sufficient for the footway side light source portion 42 to irradiate light of the spectral characteristics rich in blue-green color light to the footway 22 in comparison with the roadway side light source portion 41.
As shown as a fourth embodiment in
Number | Date | Country | Kind |
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2006-271518 | Oct 2006 | JP | national |