Analysis of design indexes for road lighting

In the dark, road users, whether drivers and pedestrians are in an extremely dangerous situation. Especially in the town on the road, the traffic situation is very complex, relying solely on automobile headlamp lighting can not meet the requirements. Some research reported in the foreign report also mentioned that on the road more than half of traffic accidents occurred at night. So the night proper lighting is very important. According to CIE's latest report shows that if the night is good road lighting, road traffic accident occurrence rate of decline of at least 30% city. The incidence of road traffic accidents in rural areas decreased by 45%, and the incidence rate of traffic accidents decreased by 30%

The road lighting not only ensures the safety of pedestrians and vehicles, but also can beautify the urban environment and provide a comfortable environment for the people

Lighting quality evaluation

A person to see objects is due to the reflected light of object surface into the eyes, the more light into the object feeling more bright. Therefore, people not only with the illuminance of road pavement L for understanding, but also with the road surface characteristics on the same road. For example, use the same road lighting facilities, people see in the rain in sunny and rainy days are different. See the road light, the former prisoners is accumulated in the surface water like a mirror, change the reflection properties of the pavement, and the feel of the road is also different.

Mainly from the aspects of visual function and visual comfort evaluation for road lighting quality. Including visual function: the average brightness of I, the overall brightness uniformity, disability glare. Visual comfort includes an average luminance edge, longitudinal uniformity, discomfort glare. The rest also includes environment due to the number of sR, visual guidance etc. will be described in detail below.

1 average brightness

Road lighting facilities to provide lighting is relatively low, the human eye is intermediary of color vision status, perceived ability is poor, then identify objects not by the color difference between to achieve, but rely on the brightness difference between the object and the background. This difference can be said to brightness and contrast:

Among them, LO is the brightness of the object itself; Z is the brightness of the background, which is the brightness of the road Z, will show a bright object contour, and the road is dark, is a positive contrast. When LO < Z, the object can show the contour, is a negative contrast

The average brightness between not only affects the object and background contrast, but also affect the visual contrast sensitivity of human. In order to influence the average brightness of research on visual function, the display capability (RP). The concept of display capability (RP) is a probability that can see the obstacles on the road to set the average brightness of figure 6.1.1. With the ability to display (RP) the relationship between the road condition is the overall uniformity is 0.4, the threshold value that the increments of 7%. in this diagram, the average brightness when the road surface is 0.6cd - m-2, display (RP) is 10%; the average brightness when the pavement is 2CD - M -2 that ability to display (RP) can be as high as 80%.

2 brightness uniformity

Good visual function requires not only a good level

All requirements between the average luminance brightness. Also on the road and the minimum brightness is not much difference. If the brightness of the field is too large, the bright part of the formation of a glare source, thus affecting the overall 'visual brightness uniformity to reflect this characteristic, it refers to the surface brightness and minimum ratio the average brightness:

The overall uniformity of UO on the display ability of RP) also have a great impact. Figure 6.1.2 is on the overall uniformity and display ability (RP) study on the relationship between the experimental road map in the closing value of incremental TT 7%. can be seen, even in the same pavement average brightness, the whole road the greater the degree of uniformity, the ability to display more. Such as the average brightness of the same as the 2CD m-2, when the overall uniformity is 0.2, display capability (RP) is only 55%; and when the overall uniformity increases to 0.4, the ability to display (RP) has risen to 80%. Therefore in road lighting not only to meet the the average brightness of the pavement, but also needs to satisfy certain uniformity, if on the road continuously and repeatedly appear bright band and dark band, namely "zebra effect" for driving in the lane for this will feel very irritable. A problem related to people's psychology, and will endanger road safety. Therefore, the severity of CIE proposed a parameter to describe the "zebra effect" -- longitudinal uniformity, it is the ratio of the minimum and maximum luminance brightness in the road lane line:

3 glare

The formation of glare is due to the presence of a high degree of brightness or brightness contrast in the field of view, so that the decline in visual function or make the eyes uncomfortable

Glare is divided into two types: disability glare and discomfort glare road users when viewing obstacles, because the glare source exists, in the eyes of a portion of the scattered light visual sense, just like in the field of Mongolia on a layer of bright screen, so the sum of people feel that the brightness of obstacles the light and brightness. So that.CIE uses a relatively closed value of incremental decline obstacle recognition ability (TT) fell because of glare caused by the visual function, namely the disability glare measure.

The relative increment threshold (Tl) is the average luminance as the background brightness, when the background brightness range of 0.05cdm-2< < LX play <5cdm-2, the approximate calculation formula of TT

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Among them, L is the average brightness of pavement; human equivalent brightness, generated from the glare source.

Figure 6.1.3 is a relatively closed value increment TT and display ability (RP) the results of the study of the relationship between the research in general maintain the road evenness is 0.4 under the same conditions, change the glare, observation showed ability in different average brightness (RP) change. See from the figure, when the average brightness of 2cdm-2 when TT was 30%, which showed greater glare, ability (RP) is 65%; when TT is 7%, the display ability (recruit up to 8D%. So the relative threshold value increment in road lighting quality measure is a very important content.

CIE also proposed the evaluation method of discomfort glare glare control 11 grade C. practice in "road lighting international recommendation", visual comfortable degree depends on the nature of the road lighting and facilities layout.