The influence of extraneous and obtrusive lights should be a part of the investigations.
New or different zones of the road lighting installation can be measured to obtain a deeper knowledge of the real situation.
For roads adopting M lighting classes, the measurement of the photometric characteristics of the road surface can be part of the investigation process. In such cases, the comparison of illuminance measurements and illuminance calculation with the required luminance values estimates the road surface conditions and gives enough information to justify discrepancies.
If necessary, for roads in a dry condition, a number of samples of the road surface should be removed for measurement under laboratory conditions or the road surface characteristics can be measured in the field with suitable instrumentations and methods able to guarantee adequate measurement uncertainty for the investigation aims.
NOTE Guidance on measurement of road surface characteristics is given in CIE 66:1984 and CIE 144:2001.Annex F
(informative)
Measurement uncertainty evaluation12)
F.lLuminance measurements
F.l.l Sources of uncertainty
The main uncertainty parameters of measuring instruments and measurement procedure to be considered are summarized in Table F.l and in Table F.2 respectively.
For measurement at the final testing phase the instability of the road lighting installation should be considered in the uncertainty evaluation.
The installation short-term instability contribution in the measurement uncertainty can be obtained from several measurements of luminance at the same point.
Table F.l and Table F.2 are not exhaustive and do not propose any grading of the relevance of different parameters. The aim is to show the importance of a genuine analysis of the metrological characteristics of the measurement system, and the need for a real understanding of the degree of influence of all the parameters that influence the outcome. It will be necessary for the person responsible for the measurements to use knowledge and experience to identify the potential for improving measurement system performance if need, and/or to identify the less important parameters that should be mentioned but need not be accurately evaluated.
It can be difficult to evaluate separately the influence of the parameters given in Table F.2. In this case the total influence of these parameters may be evaluated as a single contribution to measurement uncertainty.
Table F.l — Parameters that influence the uncertainty of luminance measurement and that are correlated to the measuring instruments
|
Instrument |
Parameter |
Notes |
|
Photo detector |
Calibration |
From the calibration certificate (see f/cai in EN 13032-1) |
|
Spectral responsivity |
To weigh the influence of the difference between the calibration source spectrum (e.g. illuminant A) and the real measured spectra (see//in EN 13032-1) In the spectra of the road reflected light is measured a correction factor can be applied and only the uncertainty of this correction shall be considered |
|
|
Directional response |
If a traditional luminance meter is sued see/2' in EN 13032-1. If a ILMD is used, to weight the lens and shutter influence on the detector responsivity, pixel by pixel considering the direction of the grid points.3 |
|
|
Linearity |
Signal linearity from the calibration certificate or by ad hoc measurement (see/3 in EN 13032-1) |
|
Instrument |
Parameter |
Notes |
|
|
Display resolution |
See/4in EN 13032-1 If an ILMD is used the effective analogue to digital A/D converter resolution of the instrument electronics shall be considered |
|
Pixel saturation in the framed field |
If an ILMD is used the influence in the measured zone of the saturation of pixels outside this zone |
|
|
Framed luminous sources in the field |
The influence in the measured zone of light sources in the surrounding field that the instrument frames (see/2,u in EN 13032-1] |
|
|
Not framed luminous sources in the field |
The influence in the measured zone of light sources the instrument does not frame, but that are present in the environments |
|
|
Noise and dark frame |
The influence of the detector noise and dark current values and repeatability if a ILMD is used, the values are obtain pixel by pixel from dark frames |
|
|
Focusing |
The influence of being out of focus if the measured zone is not at the right distance (see/12 in EN 13032-1] |
|
|
Influence of non-uniform illumination of the acceptance areas of the framed zone |
The construction of some photometer heads lead to a significant dependence of the responsivity (including the relative spectral responsivity] on the incident-light position in the acceptance area (see/9 in EN 13032-1]. If an ILMD is used, only the detector surface were the measuring zone is framed shall be considered. |
|
|
Other parameters defined in EN 13032-1 |
The influence of the other performance parameters specified in EN 13032-1 as a whole or parameter by parameter |
|
|
a Guidance on the characterization of ILMD is under consideration. |
||
Table F.2 — Parameters that influence the uncertainty of luminance measurement and that are
correlated to the measurement procedure
|
Measurement procedure |
||
|
Parameter |
Description |
Notes |
|
Point identification |
Influence of the uncertainty in the point coordinates |
If road markers are used, accuracy of alignment and positions of the markers |
|
Influence of the perspective correction algorithm |
If a perspective correction algorithm is used, accuracy of the calculated measurement point coordinates derived from the accuracy of the road reference point and of the perspective correction algorithm |
|
|
Measurement area |
Influence of the effective area of the point of measurement |
Dimension of the framed surface used to acquire the point of luminance |
|
Real position |
Influence of the real camera position compared to the nominal position |
Influence of tolerances respect to the nominal position required in this standard or Influence of the different detector position. |
F.1.2 Additional uncertainty sources for dynamic systems
Many sources of uncertainty are more critical in dynamic measurement systems than in static ones and some sources are typical of dynamic systems.
The vehicle speed is an important factor. The use of particular parameters (see 3.5) is suggested to better describe the measured quantities.
If only one transit is done, only one measure for point is possible. If required, the installation short-term instability, should be obtained or estimated from ad hoc measurements carried out in a zone of the installation for a period of time at least equal to the time spends for the dynamic measurement of the same installation.
A non-exhaustive description of particular uncertainty sources is in Table F.3 for parameter correlated to measuring instruments and in Table F.4 for parameter correlated to measurement procedure. These tables shall be read as an addendum of Table F.l and of Table F.2 respectively.
Table F.3 —Additional parameters of Table F.l that influence the uncertainty of luminance measurement carried out with dynamic systems
|
Instrument |
Parameter |
Notes |
|
Photo detector |
Influence of movement |
The measured area is longer for the movement of the vehicle. For example at 90 km/h and with exposure time of 20 ms the space is 0,5 m |
Table F.4 — Additional parameters of Table F.2 that influence the uncertainty of luminance measurement carried out with dynamic systems
|
Parameter |
Description |
Notes |
|
Point identification |
Influence of the uncertainty in the point coordinates |
Accuracy in defining the position of the dynamic system detector/detectors with respect to the initial reference point and thereafter the measurement points with respect to the installation |
|
Measurement area |
Influence of the effective area of the point of measurement |
Dimension of the framed surface used to acquire the point of luminance shall consider the vehicle movement |
|
Real position |
Influence of the real camera position compared to the nominal position |
Influence of tolerances with respect to the nominal position required in this standard. Both longitudinal and transverse positions are important Detector tilting affects the measurement distance |
F.1.3 Evaluation of point luminance uncertainty
In this example the uncertainty of the measurement system is considered, and not that of the influence of the road lighting installation, measurement point position and weather.
In the proposed model of the measurement procedure the dark image reading, the influence of sources within and outside the frame and ghost images are subtracted from the detector reading. The result shall be multiplied by the calibration coefficient and by other correction factors correlated to parameters described in CIE S 023/E:2013. Their value is usually unity.
The point measured luminance Lm is:
= (*m -«d "«i ~R0-R^K^K^.K^K^K^K^K^ (F.l)
whereRm is the detector reading (measure image);
Ri is the detector reading (dark image);
Ri is the signal due to luminous sources inside the frame;
Ro is the signal due to luminous sources outside the frame;
Rg is the signal due to ghost images;
Kcai is the detector calibration;
, is the detector V(A) match;
Kf is the detector directional responsivity;
Kf3 is the detector linearity;
is the detector A/D real resolution;
Kf is the influence of focusing distance;
Kf is the influence of other, generally less important performance parameters described in cie CIE S 023/E:2013.
NOTE 1 In well-designed measurement system R„ Ro, and Rg are usually negligible, compared to and Rd therefore only their uncertainty is important.
NOTE 2 In dynamic measurement systems only one measurement is carried out so the standard uncertainty of Rm is equal to the repeatability of the luminance meter.
NOTE 3 Usually in ILMD all the parameter of the proposed model (Formula F.l) are different from pixel to pixel.
F.2 Illuminance measurements
F.2.1 Sources of uncertainty
The main uncertainty parameters of measuring instruments and measurement procedure to be considered are summarized in Table F.5 and in Table F.6 respectively.
For measurement at the final testing phase the instability of the road lighting installation shall be considered in the uncertainty evaluation.
The installation short-term instability contribution in the measurement uncertainty can be obtained from several measurements of illuminance at the same point.
Table F.5 and Table F.6 are not exhaustive and dos not propose any grading of the relevance of a different parameter. The aim is to show the importance of a genuine analysis of the metrological characteristics of the measurement system and of the need for a real understanding of the degree of influence of all the parameters that influence the outcome. It will be necessary for the person responsible for the measurements to use knowledge and experience to identify the potential for improving the measurement system performance if needed and/or to identify the less important parameters that should be mentioned but need not be accurately evaluated.
It can be difficult to evaluate separately the influence of the parameters given in Table F.6 under the set "Measurement procedure". In this case the total influence of these parameters may be evaluated as a single contribution to measurement uncertainty.
Table F.5 — Parameters that influence the uncertainty of illuminance measurement and that are correlated to the measuring instruments
|
Instrument |
Parameter |
Notes |
|
Photo detector |
Calibration |
From the calibration certificate (see t/cai in EN 13032-1) |
|
Spectral responsivity |
To weigh the influence of the difference between the calibration source spectrum (e.g. illuminant A) and the real measured spectra [see fi in EN 13032-1) If the spectra of the incident light is measured a correction factor can be applied and only the uncertainty of this correction shall be considered. |
|
|
Directional responsivity |
To weight the influence directional responsivity see f2 in CEN/TR 13201-1 |
|
|
Linearity |
Linearity in the measured range can be found in the calibration certificate or can be estimated by ad hoc measurement (see /3 in EN 13032-1) |
|
|
Display resolution |
See/rin EN 13032-1 |
|
|
Change of scale |
See/ц in EN 13032-1 |
|
|
Noise and dark current |
The influence of detector noise and dark current values and repeatability |
|
|
Other parameter defined in EN 13032-1 |
The influence of the other performance parameters specified in EN 13032-1 as a whole or parameter by parameter |
Table F.6 — Parameters that influence the uncertainty of illuminance measurement and that are correlated to the measurement procedure
|
Parameter |
Description |
Notes |
|
Point identification |
Influence of the uncertainty in the point coordinates |
If road markers are used, accuracy of alignment and positions of markers |
|
Measurement area |
Influence of the effective area of the point of measurement |
This term can be neglected for most detectors in general use |
|
Real position |
Influence of the real detector position compared to the nominal position |
See point identification and detector real position and tilt condition compared to nominal condition |
F.2.2 Additional uncertainty sources for dynamic systems
Many source of uncertainty are more critical in dynamic measurement systems than in static ones. For example in split detector systems, the actual directional sensitivity shall be obtained considering tolerances in the position of the two detectors and of their tilt.
Also the vehicle speed is important because it can increase the above mentioned tolerances and measured area (see the introduction of particular parameters in 3.5).
If only one transit is done, only one measure for point is possible. If required, the installation short-term instability, should be obtained or estimated from ad hoc measurements carried out in a zone of the installation for a period of time at least equal to the time spends for the dynamic measurement of the same installation.
A non-exhaustive description of peculiar uncertainty sources is in Table F.7 for parameter correlated to measuring instruments and in Table F.8 for parameter correlated to measurement procedure. These tables shall be read as an addendum of Table F.5 and of Table F6 respectively
Table F.7— Additional parameters of Table F.5 that influence the uncertainty of illuminance
measurement carried out with dynamic systems
|
Measuring instruments |
||
|
Instrument |
Parameter |
Notes |
|
Photo detector |
Directional responsivity |
To weigh the influence of the detector shields. In split detector system two readings are summed when the two detectors are in the same nominal position |
|
Linearity |
In the range of measured values. The measuring range can be different from the minimum and maximum road illuminance because singe hemisphere are considered. The measuring scale cannot be the best one because it can be known only after measurement |
|
|
Change of scale |
To avoid out of range conditions a predictive change of amplifier gain can be adopted |
|
Table F.8— Additional parameters of Table F.6 that influence the uncertainty of illuminance
measurement carried out with dynamic systems
|
Measurement procedure |
||
|
Parameter |
Description |
Notes |
|
Point identification |
Influence of the uncertainty in the point coordinates |
Accuracy in defining the detector positions considering the three special coordinates. According to the system characteristics the uncertainty of the longitudinal coordinate can increase with the measuring distance. |
|
Measurement area |
Influence the effective area of the point of measurement |
Vehicle speed and sampling period |
|
Total illuminance |
Influence of the real detector position compared to the nominal position |
The signal of the two detectors are not acquired at the same point |
|
Real position |
The three parameters of Table F.6 |
These parameters can be evaluated as a single contribution to measurement uncertainty. In split detector system, the tilt angle and the three special coordinate during the sampling time shall be considered for the front and rear detectors and discrepancies between the two resolved when the total illuminance is evaluated. Usually the horizontal illuminance is measured with the detector parallel to the road surface |
F.2.3 Evaluation of point illuminance uncertainty
The evaluation of uncertainties can be simplified using a model similar to that described for luminance measurements (see F.1.3). For illuminance, the uncertainty in the detector position plays an important role in increasing the expanded uncertainty and shall be evaluated when considering the light distribution on the road surface.Annex G
(informative)
Practical information
G.l General
This annex gives practical information that is useful for preparing measurement procedures.
The example given should be adapted where not all parts are relevant.
G.2 Measurement precautions
The following is a non-exhaustive list of precautions that should be considered to avoid wrong measurement or inaccuracies:
check position and orientation of the instrument;
spectral sensitivity adequately corrected for the type of lamp used (i.e. LED);
possible instrument damage during manipulation and transport;
preliminary testing of instrument before starting the measurement procedure;
calibration certificate not expired;
battery in good condition;
instrument warm-up in accordance with manufacture instructions;
dark current compensation or auto calibration;
correct choice of instrument range.
G.3 Measurement organization
The use of check lists facilitate the organization of the measurement campaign and avoid the oversight of important steps or precautions especially when the measurement activity is carried out in hard conditions.
For luminance measurement, in advance of taking measurements, it can be convenient to mark out the relevant grid on the road surface with markers which allow the meter to be correctly aligned, for example when they are viewed through the viewfinder of the luminance meter. If they appear in the measuring cone of the luminance meter they should be removed before a measurement is taken.
