Analysis of results of emission parameters of advertising media in field conditions

The lighting parameters of advertising media observed from the road leading drivers are one of the basic factors which should be taken into account in the process of determining the influence of the carrier on the risk related to the possibility of a road event. As a result, exceeding the permissible parameters may lead to disturbance of the vision process or distraction from the driver's primary objective, which is to observe the road situation. The article presents the results of tests of lighting and geometric parameters carried out on a large number of advertising media located in the vicinity of Polish roads. The study was conducted at night, using an original research procedure. Observation of advertising media from the driver's position is included. The final result of the work is information about the actual levels of lighting parameters generated by a large group of advertising media of different character of light beam emission (broken down into defined emission groups A D), which can be observed from the driver's position.


Introduction
The lighting parameters of advertising media observed from the road by drivers are one of the basic factors that should be taken into account when determining the impact of the media on the risk related to the possible occurrence of a road event [1,2]. Measurement of important technical and lighting parameters, their collection, cataloguing and analysis are crucial to determine the permissible ranges of variability and to indicate the prohibited values. Conducting field research on advertising media involves numerous restrictions resulting from the existing measurement conditions, location, geometric and emission parameters of the media itself and the environment in which it occurs. The developed procedure [3,4] used to measure emission parameters takes into account the listed factors and enables unambiguous identification of the limit values of the measured parameters.
Negative lighting effects of advertising media on drivers may result in a traffic hazard [5][6][7]. This hazard may be due to excessive luminance or contrast within the driver's field of vision. As a result, exceeding the limit values may lead to abnormal vision or distraction of the driver from the primary objective of observing the driving situation.
The main aim of the research issue discussed in the article is to perform lighting measurements of a large group of advertising media and to search for links between the light and photometric values and their influence on possible disturbances of the driver's vision process.
2 Field research of a selected group of advertising media A group of media containing advertising representatives with different methods of light beam emission (group "A" -light source, group "B" -frontlight, group "C" -backlight, group "D" -without backlighting) was selected for the field research. Each advertising medium was visible from the roadway. The choice of location served to present the problem of the impact of advertising in different regions of Poland.

Location of advertisement tested
A total of 339 media were measured. In order to select a representative group, the measurement results for 230 advertisement were evaluated further. The measurements were taken at night, in good weather conditions for three locations: Gdańsk -Tczew, Warsaw -Brand name and Łomianki.

Photometric parameters to be tested
The measurement data consist of the following characteristics of the advertisement: Additionally, a contrast of the luminance of the advertising surface with the background, which is a ratio of the difference of the luminance of the observed object and the background luminance to the background luminance, was calculated for each medium on the basis of the obtained data. The luminance contrast [3] can be calculated from formula (1): where: -the maximum value of the luminance of the advertising medium (cd/m 2 ), ś -the mean value of the ambient luminance, background of the advertising medium (cd/m 2 ).

Methodology used for the measurements
In order to perform the measurements of lighting and geometric quantities, the author's research procedure [3,4] was applied, the most important assumptions of which are as follows: measurement in favourable meteorological conditions (no rainfall, ambient temperature within the range permissible for measuring instruments, good atmospheric transparency), -measurement from the direction of maximum light beam emission -perpendicular to the position of the advertising medium ( Fig. 2), -measurement distance depending on the size of the measuring field in order to ensure discreetness of the media surface at the level of 1/100 of its geometric dimensions (the measurements used a matrix and a point control meter with a variable measuring field from 6' to 3 0 ), -for safety reasons, measurement from the edge of the road and not from the eye of the driver of the vehicle, but at the correct height of 1,5 m above the road surface. Selection of the measurement fields for of the media surface and the ś of the observation background (the media environment) using a CCD matrix meter is shown in Figure 3.

Results of measurements of lighting parameters of advertising media together with analysis of collected data
The results of lighting and geometrical measurements were collected in a database and subjected to statistical analysis. Table 1 shows the average size for all media groups: maximum media luminance (LNmax), area, and contrast [C]. The standard deviation of the spread width of the measured values in relation to the mean is given. Additionally, the luminance value of the mean background (LTśr) was determined. It is clear from the data that the most negative impact on the driver in terms of dazzling potential is exerted by advertisements in the "A" and "C" groups. They also generate the highest contrast. However, ads in the "A" group have the smallest surface area and the largest statistical spread of medium contrast. It may happen that despite the high luminance value of the surface and the contrast, the advertisement will have a small impact due to its small surface area and small angular size. Conversely, reverse situations are also possible (low luminance and contrast, but large surface and angular sizes -e.g. group "B"), which may be underestimated by researchers and, as a result, become a road traffic hazard.       In the opinion of the authors of the publication, the photometric values that characterise an advertising medium should relate to the geometric surface and the size of the angular advertisement as seen from the driving position of the passenger vehicle. Advertisements with high maximum luminance are usually of small angular size (small area, setting at a small angle to the road) - Fig. 4.5. The same applies to contrast analysis (Fig. 6.7). Lighting guidelines, apart from limiting the lighting parameters, should define precise geometrical values. When an advertisement is of high quality ( ) it should be small in size and placed as parallel to the road as possible.

Summary
The studied advertising media did not exceed the level of 250 cd/m 2 for maximum luminance. The Landscape Act [9] allows for: 600 cd/m 2 at night in a built-up area and 400 cd/m 2 outside a built-up area. Despite the relatively low level of brightness, some media had a negative impact on the driver, which was caused by the high contrast between the luminance of the advertisement and the background (advertising located in a dark environment) and a large angle to the road (setting close to perpendicular), which significantly increased the angular size of the object and thus the value of the luminance of mist affecting the level of glare. The analysis of the research results has shown unequivocally that there are situations in which the maximum luminance levels adopted in the Landscape Act are too high. The guidelines should refer very precisely to the illumination level of the background observation in the advertising environment. Large-format advertising should have a stricter criterion for acceptable luminance levels because of its large angular size. The research also confirmed that advertisers largely complied with the provisions of the Landscape Act and reduced the levels of brightness (luminance) of the visual information carriers (the attention concerns mainly advertising from the "A" group -LED telebims). Further research works are indicated and are to result in precisely defined lighting, geometric and location guidelines for advertisements, which reduce the negative impact of advertisements on the driver's vision process. Defined permissible levels of technical parameters and repeatable measurement procedures will allow for effective control and verification to eliminate road traffic hazards generated by advertising seen from the road.