Summary and Conclusion of Glare Perception For Short Light Pulses

158 analysis and optimization of light distributions

5.3.3 summary and conclusion of glare perception for short light pulses

5.3 glare perception for short light pulses 159 andunbearable. Since all surrounding parameters, like adaptation time and surrounding lu-minance, are kept the same, this is only explained by the way both tests are performed. In both parts, a selection of the lowest and the highest pulses are shown for the test participants as anchor stimuli. The possible explanation for this behaviour is, that due to these anchor stimuli are unconsciously used to sort all shown glare pulses onto the de Boer scale and thereby resulting in two separate data sets.

This subconscious behaviour also explains the general form found in the glare ratings. The expected results of both studies were to receive a s-curve for the glare ratings. For very very low light pulses no glare should be perceived and going even lower should not change this perception. The same is expected at the upper bounds. Beyond a certain threshold, every light pulse should be perceived as unbearable. However, due to the assumed subconscious sorting of all pulses according to the anchor stimuli, both maximum and minimum of the glare pulses are associated with the maximum and the minimum of thede Boer scale. All other glare pulses are then sorted linearly (on the logarithmic scale) between these anchor stimuli.

comparing the data to related work

As described in chapter 4 several studies have examined the correlation between the psy-chological glare perception and different photometric values. This section will now focus on comparing the results from this study with the results found by Lehnert who found a cor-relation between the illuminance, the pulse duration and thede Boerrating and the results from Zydek who found a correlation between the exposure and the de Boer rating in real life driving tests [55].

As explained in chapter4 the test setup for both Lehnertand Zydek are more real life test setups and therefore the comparison between the results achieved in the laboratory study in this thesis and their results achieved under completely different setups is highly relevant since the translation from the laboratory experiments to the real life tests is one of the goals of this study. The formula provided by Lehnertis dependent of the pulse duration, his glare rating is calculated for the same experimental setup as in the first part of this study. Since this thesis used the invertedde Boer scale, the data obtained in this thesis is transformed to the originaldeBoer scale as well. This means, that in this case, a rating of 9 corresponds to a glare peak that isjust noticeableand a rating of 1 means an unbearableglare peak is per-ceived. This is shown in figure 5.63 where the data obtained by the equation 4.1 is shown in the dashed lines compared to the data obtained in this study. The same is done for the glare rating obtained by Zydekin figure5.64. However, since the work of Zydekis based on exposure calculated over a longer period of time (18 s) it is not possible to convert his data into illuminance data or to split his ratings into different pulse widths.

160 analysis and optimization of light distributions

0.1 1 10 100

1 2 3 4 5 6 7 8 9

Illuminance in lx

deBoerRating

Lehnert 128 ms Lehnert 320 ms Lehnert 800 ms Lehnert 2000 ms Kobbert 128 ms Kobbert 320 ms Kobbert 800 ms Kobbert 2000 ms

Figure5.63– Comparison of the glare perception on thedeBoerscale between the glare perception accord-ing to Lehnert(dashed) over the pulse illuminance.

It can be seen, that while the range of the photometric values is similar, the resulting glare is indeed different. While the data shown by Lehnertshows a similar slope, his illuminance pulses are in general rated more glaring than the data presented in this thesis. However, while the data obtained in this thesis is parallel over different durations, the data shown by Lehnertwidens up for higher illuminance values. The data shown by Zydek shows the exact opposite in terms of behaviour. The overall rating is fairly similar, however the slope is much higher in his case.

0.1 1 10 100

1 2 3 4 5 6 7 8 9

Exposure in lx·^s

deBoerRating

Zydek

Kobbert 128 ms Kobbert 320 ms Kobbert 800 ms Kobbert 2000 ms

Figure5.64 – Comparison of the glare perception on the deBoer scale between previous work and the results from the experiments shown above, the data as found by Zydek(dashed) over the exposure.

5.3 glare perception for short light pulses 161 Here it can be seen, that while the range of the photometric values is similar, the resulting

glare is indeed different. While the data shown by Lehnertshows a similar slope, his illumi-nance pulses are in general rated less glaring than the data presented in this thesis. A special remark needs to be made to the dependence on the duration. The shorter the pulse duration, the smaller the deviations between the two works. This overall lesser rating is expected since the additional stress in the real life test is much higher compared to the situation in the lab-oratory. Additionally, it can be assumed, that the background luminance in the laboratory is much significantly lower compared to Lehnert’sreal life test, thereby increasing the per-ceived glare as well. However, while the data obtained in this thesis is parallel over different durations, the data shown by Lehnert widens up for higher illuminance values. The data shown by Zydekshows the exact opposite in terms of behaviour. The overall rating is fairly similar, however the slope is much higher in his case.

This again shows, similar to the data presented in figure 5.62, that the glare rating is very much dependent on the current situation and the other glare sources presented to the test subjects. If the overall range of the glare pulses/sources is smaller, the slope will increase. If the range is about the same, but the pulses/sources are shifted in terms of their photometric values, the overall rating will be shifted as well.

summary, conclusion and outlook on glare and pupillometry studies The goal of the studies is, to find a strong correlation between a physiological parameter and the glare perception of the test participants and transfer this data to real life driving tests.

To achieve this, two main studies are performed. In the first part, the correlation between the photometric values illuminance and exposure, the glare rating and the pupil diameter are found with very good results for the correlation between both,deBoerrating and pupil diameter and modified exposure, respectively. In the second part, the rectangle pulses were changed to triangle pulses and the findings here, indicated a better correlation to the illumi-nance for longer pulse durations. Nevertheless it can be concluded that a pulse with rising edges (triangle) is always perceived less glaring than a rectangular pulse no matter what photometric value is used.

The main point, that can be taken from these two studies with regards to the correlation be-tween photometric values and glare perception is, that neither exposure nor illuminance are correlating values over the investigated data range. The correlation found is best described by equation5.20.

G = E·^{Tp (5.20)}

From the data presented, it is concluded, thatpis not a specific value but rather dependent onT, the pulse duration and the equation therefore needs to be modified to equation5.21.

G = E·^{Tp(T) (5.21)}

Taking into account all the data shown in both studies, three major regions appear. For pulse durations smaller than 300 ms the best correlation between the glare rating and the exposure is found. For medium pulse durations between 300 ms and up to around 2000 ms the correlation is optimized for E·^T0.47 and for longer pulses the correlation is found to be best in line with the illuminance and the duration does not interfere at all. This leads to the following equations5.22:

162 analysis and optimization of light distributions

if T < 300 ms

p = 1 (5.22a)

if 300 ms < T < 2000 ms

p ≈ ^{0.5 (5.22b)}

if 2000 ms < T

p = 0 (5.22c)

Since the obtained data only covers specific points, a discrete function ofpas presented is not realistic. Figure5.65shows an approximation of the suggested behaviour. The dotted purple line indicates the suggested behaviour of pand the three data sets indicate the findings for p at the three different pulse durations.

0 500 1,000 1,500 2,000 2,500 3,000

0 0.2 0.4 0.6 0.8 1

Pulseduration T in ms

pina.u.

T <300 ms

300 ms < T < 2000 ms T > 2000 ms

fitted curve

Figure5.65– Suggested bahaviour ofp(equation5.21. The suggested behaviour is indicated by the dashed purple line and the data points show the findings for the different pulse durations.

The proposed function in figure5.65is only an approximation with only three major avail-able data points. The fit function is given in equation5.23. With only three data points, both the x-shift (indicated by −^T+990) and the slope (indicated by the x^−0.02) need to be in-vestigated further. Using this factor, it is then possible to evaluate the glare perception for different light pulses even with varying durations. The main issue here is, when comparing both studies, that due to the presented anchor stimuli, no absolute assessment can be done.

p(T) = ¹

(1+e^(−T+990))^{−0.02 (5.23)}

However, the investigated pulses are only simplified approximations of the illuminance val-ues recorded in real life driving tests. Additionally, to that more limitations to the performed studies have to be mentioned: