# Influence of Headlight Level on Object Detection in Urban Traffic at Night

^{*}

## Abstract

**:**

## 1. Introduction

^{−2}there is a direct correlation between roadway luminance and the night/day crash ratio; moreover, an increase in roadway luminance of $1.0$ $\mathrm{cd}$ $\mathrm{m}$

^{−2}results in a reduction in this ratio of approximately 35%. Similar results regarding the reduction of the required contrast at higher roadway or adaptation luminances can be found in studies by Damasky [13] or Blackwell [27].

^{−2}. Observers were asked to indicate recognition by a forced-choice procedure. It is noteworthy that the slope of the multiplier increased significantly from the age of 64 [32].

- $\Delta {L}_{th}$: Threshold luminance difference
- k: Detection probability factor
- ${\left({\displaystyle \frac{\sqrt{\Phi}}{\alpha}}+\sqrt{L}\right)}^{2}$: Luminous flux and luminance function according to Ricco’s and Weber’s laws
- $\alpha $: Object size in angular minutes
- $a(\alpha ,{L}_{B})$: Blondel-Rey constant
- t: Observation time in seconds
- ${F}_{CP}$: Contrast polarity factor
- $AF$: Age factor

- (1)
- What is the influence of different road illumination levels and luminous intensities of motor vehicle headlights on the detection of objects at different distances and angular positions in front of the vehicle?
- (2)
- What influence does the intensity of the low beam have on the contrast polarity and value of flat detection targets on illuminated roads with different illumination levels?
- (3)
- Is there an optimized urban light distribution for motor vehicle headlights, and if so what should it look like?

## 2. Materials and Methods

#### 2.1. Test Roads

^{−2}for test road 1 to $0.53$ $\mathrm{cd}$ $\mathrm{m}$

^{−2}for test road 2 and $0.38$ $\mathrm{cd}$ $\mathrm{m}$

^{−2}for test road 3; see Figure 2. From the luminance images, the differences in the homogeneity of the street lighting are evident, as are the different roadway brightnesses. The luminance recordings were carried out with a luminance camera (TechnoTeam LMK 5 color) attached to the rearview mirror of the test vehicle in order to realize the measurement from the driver’s point of view.

#### 2.2. Test Vehicle

#### 2.3. Test Procedure

^{2}flat targets with a reflectance of about 4% (exact value $3.956$%), were placed on a measurement grid which had four objects per row at distances of 30 $\mathrm{m}$, 45 $\mathrm{m}$, 55 $\mathrm{m}$, and 65 $\mathrm{m}$. A low reflectance was chosen because according to studies by Randrup Hansen and Schandel Larsen [65] or Schneider [66], the clothing of pedestrians has low reflectance values of less than 10%, especially in the winter. The reflectance of the flat targets was determined by comparative measurements with a reflectance standard. Furthermore, two different vehicle positions were considered. In the first, the vehicle is placed directly under a street light system, while in the second, the vehicle is moved 10 $\mathrm{m}$ in the direction of the measurement grid, creating a second situation for the detection of objects with distances of 20 $\mathrm{m}$, 35 $\mathrm{m}$, 45 $\mathrm{m}$, and 55 $\mathrm{m}$. The applied measurement grids are shown in Figure 4.

#### 2.4. Measurements

- $\alpha $: stimulus of the halfway point
- $\beta $: steepness of the function
- $\gamma $: probability of a positive response by chance; here, $\gamma =0$.

## 3. Results

#### 3.1. Photometric Results

^{−2}, as here this second threshold for object positions 5 to 16 cannot be reached at all with the existing headlight system. On test roads 2 ( $0.53$ $\mathrm{cd}$ $\mathrm{m}$

^{−2}) and 3 ( $0.38$ $\mathrm{cd}$ $\mathrm{m}$

^{−2}), the same applies to the objects at a distance of 65 m. In these cases, the low beam function merely causes a downgrading of the visibility conditions, and achieves the opposite of its actual function of improving visibility. This transition from negative to positive contrast is illustrated by the luminance images in Figure 9.

^{−2}). Thus, for both vehicle positions, there is no object position where the Visibility Level is less than 1. This means that the threshold luminance difference from Adrian’s Small Target Visibility Model is achieved with fully activated low beam for all object positions. Compared to test road 1, the number of critical object positions with Visibility Levels less than 7 decreases from 9 to 3 out of 16 positions for vehicle position 1 and from 5 to 0 for vehicle position 2.

#### 3.2. Subject Study Results

^{−2}. Here, with the low beam fully switched on, only the flat targets on 6 out of 16 object positions are detected with a probability of over 90%, while with the low beam switched off the flat targets are already detected on 15 out of 16 object positions with a probability of over 90%. It is noticeable that with the low beam switched on, the detection probability for the flat targets is above the critical threshold of 50% on only 12 out of 16 positions on test road 1. Looking at the darker test roads, it can be seen that the number of objects detected with the considered probabilities are in a similar range for both switched off and fully switched on low beam.

## 4. Discussion

- (1)
- What is the influence of different road illumination levels and luminous intensities of motor vehicle headlights on the detection of objects at different distances and angular positions in front of the vehicle?

^{−2}) to 10 (test road 2, $0.53$ $\mathrm{cd}$ $\mathrm{m}$

^{−2}) to 12 out of 16 positions (test road 3, $0.38$ $\mathrm{cd}$ $\mathrm{m}$

^{−2}) for vehicle position 1. The same trend results for vehicle position 2. Here, the number increases from 12 (test road 1) to 13 (test road 2) to 15 (test road 3) out of 16 positions with secure object detection. This correlation between the illumination level of the road and low beam effectiveness has previously been shown by Bullough [53]. Thus, the present study confirms previous findings in the literature showing that low beam effectiveness decreases as the level of illumination increases.

- (2)
- What influence does the intensity of the low beam have on the contrast polarity and value of flat detection targets on illuminated roads with different illumination levels?

- (3)
- Is there an optimized urban light distribution for motor vehicle headlights, and if so, what should it look like?

## 5. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**Test roads on which the study was conducted: (

**top left**) test road 1 (M4 class); (

**top right**) test road 2 (M5 class); (

**bottom**) test Road 3 (M6 class).

**Figure 2.**Luminance images of the test roads on which the study was conducted: (

**top left**) test road 1 ( $0.91$$\mathrm{cd}$ $\mathrm{m}$

^{−2}, M4 class); (

**top right**) test road 2 ( $0.53$$\mathrm{cd}$ $\mathrm{m}$

^{−2}, M5 class); (

**bottom**) test Road 3 ( $0.38$$\mathrm{cd}$ $\mathrm{m}$

^{−2}, M6 class). From the luminance images, the homogeneity differences are obvious.

**Figure 3.**Dimmed low beam distributions of the BMW 3 Series LED headlight used in the tests; PWM dimming changes the absolute intensity of the low beam distribution, while the light distribution itself remains unaffected by the dimming.

**Figure 4.**Test setup for the detection investigations: (

**left**) measurement grid with four flat targets each at distances of 30 m, 45 m, 55 m, and 65 m; (

**right**) measurement grid with four flat targets each at distances of 20 m, 35 m, 45 m, and 55 m. The numbers on the flat targets indicate the internal position identifier.

**Figure 5.**Example of data evaluation using the psychometric function acoording to Linschoten [68].

**Figure 6.**Contrast curves on test road 1 ( $0.91$ $\mathrm{cd}$ $\mathrm{m}$

^{−2}) and vehicle position 1 depending on the intensity percentage from 0% (low beam off) to 100% (low beam fully switched on).

**Figure 7.**Contrast curves on test road 2 ( $0.53$ $\mathrm{cd}$ $\mathrm{m}$

^{−2}) and vehicle position 1 depending on the intensity percentage from 0% (low beam off) to 100% (low beam fully switched on).

**Figure 8.**Contrast curves on test road 3 ( $0.38$ $\mathrm{cd}$ $\mathrm{m}$

^{−2}) and vehicle position 1 depending on the intensity percentage from 0% (low beam off) to 100% (low beam fully switched on).

**Figure 9.**Illustration of the transition from negative contrast to positive contrast; the two objects in the middle are clearly visible with the negative contrast (

**left**), while an increase in the low beam intensity leads to a neutralization of the contrast and makes the objects disappear (

**center**) and a further increase in the low beam intensity makes the objects visible again (

**right**).

**Figure 10.**Object position 15 on test road 2; detection conditions are made more difficult by the position of the flat target directly in front of the fixation object.

Test Road | ${\mathit{L}}_{\mathit{m}}$ in cd m ${}^{-2}$ | ${\mathit{U}}_{0}$ | ${\mathit{U}}_{1}$ | Class |
---|---|---|---|---|

1 | 0.91 | 0.35 | 0.66 | M4 |

2 | 0.53 | 0.30 | 0.42 | M5 |

3 | 0.38 | 0.32 | 0.40 | M6 |

Low Beam off | ||||

30 $\mathrm{m}$ | 45 $\mathrm{m}$ | 55 $\mathrm{m}$ | 65 $\mathrm{m}$ | |

$-3.0$$\mathrm{m}$ | 33.70 | 24.91 | 17.23 | 13.44 |

$-1.5$$\mathrm{m}$ | 33.33 | 22.27 | 14.82 | 12.51 |

$0.0$$\mathrm{m}$ | 35.18 | 24.03 | 14.01 | 10.96 |

$1.5$$\mathrm{m}$ | 40.21 | 28.21 | 24.07 | 17.12 |

Low Beam fully switched on | ||||

30 $\mathrm{m}$ | 45 $\mathrm{m}$ | 55 $\mathrm{m}$ | 65 $\mathrm{m}$ | |

$-3.0$$\mathrm{m}$ | 31.87 | 4.00 | 4.03 | 2.92 |

$-1.5$$\mathrm{m}$ | 88.68 | 10.34 | 0.06 | 4.78 |

$0.0$$\mathrm{m}$ | 81.46 | 6.12 | 2.85 | 0.91 |

$1.5$$\mathrm{m}$ | 33.19 | 4.09 | 12.06 | 9.56 |

Low Beam off | ||||

20 $\mathrm{m}$ | 35 $\mathrm{m}$ | 45 $\mathrm{m}$ | 55 $\mathrm{m}$ | |

$-3.0$$\mathrm{m}$ | 40.16 | 33.11 | 23.38 | 17.99 |

$-1.5$$\mathrm{m}$ | 39.45 | 28.68 | 20.92 | 15.63 |

$0.0$$\mathrm{m}$ | 42.21 | 31.14 | 21.17 | 15.88 |

$1.5$$\mathrm{m}$ | 48.19 | 33.76 | 31.38 | 21.35 |

Low Beam fully switched on | ||||

20 $\mathrm{m}$ | 35 $\mathrm{m}$ | 45 $\mathrm{m}$ | 55 $\mathrm{m}$ | |

$-3.0$$\mathrm{m}$ | 31.35 | 16.58 | 6.66 | 5.03 |

$-1.5$$\mathrm{m}$ | 149.04 | 34.15 | 17.31 | 4.95 |

$0.0$$\mathrm{m}$ | 169.81 | 38.78 | 25.40 | 9.17 |

$1.5$$\mathrm{m}$ | 54.34 | 20.08 | 2.54 | 0.57 |

Low Beam off | ||||

30 $\mathrm{m}$ | 45 $\mathrm{m}$ | 55 $\mathrm{m}$ | 65 $\mathrm{m}$ | |

$-3.0$$\mathrm{m}$ | 25.35 | 14.62 | 11.28 | 8.76 |

$-1.5$$\mathrm{m}$ | 27.75 | 16.47 | 10.31 | 7.23 |

$0.0$$\mathrm{m}$ | 30.14 | 16.42 | 10.75 | 8.21 |

$1.5$$\mathrm{m}$ | 21.80 | 21.03 | 16.73 | 16.00 |

Low Beam fully switched on | ||||

30 $\mathrm{m}$ | 45 $\mathrm{m}$ | 55 $\mathrm{m}$ | 65 $\mathrm{m}$ | |

$-3.0$$\mathrm{m}$ | 53.81 | 24.97 | 6.91 | 8.31 |

$-1.5$$\mathrm{m}$ | 74.27 | 23.82 | 8.96 | 6.46 |

$0.0$$\mathrm{m}$ | 116.84 | 31.59 | 14.69 | 10.05 |

$1.5$$\mathrm{m}$ | 93.59 | 23.24 | 12.53 | 2.84 |

Low Beam off | ||||

20 $\mathrm{m}$ | 35 $\mathrm{m}$ | 45 $\mathrm{m}$ | 55 $\mathrm{m}$ | |

$-3.0$$\mathrm{m}$ | 32.83 | 22.16 | 21.38 | 13.34 |

$-1.5$$\mathrm{m}$ | 34.09 | 22.48 | 20.78 | 11.69 |

$0.0$$\mathrm{m}$ | 36.98 | 22.38 | 18.85 | 8.87 |

$1.5$$\mathrm{m}$ | 26.00 | 30.36 | 23.09 | 20.42 |

Low Beam fully switched on | ||||

20 $\mathrm{m}$ | 35 $\mathrm{m}$ | 45 $\mathrm{m}$ | 55 $\mathrm{m}$ | |

$-3.0$$\mathrm{m}$ | 70.15 | 52.23 | 18.66 | 9.82 |

$-1.5$$\mathrm{m}$ | 152.23 | 63.35 | 27.58 | 16.63 |

$0.0$$\mathrm{m}$ | 247.55 | 72.39 | 39.44 | 21.67 |

$1.5$$\mathrm{m}$ | 162.93 | 50.33 | 32.80 | 8.22 |

Low Beam off | ||||

30 $\mathrm{m}$ | 45 $\mathrm{m}$ | 55 $\mathrm{m}$ | 65 $\mathrm{m}$ | |

$-3.0$$\mathrm{m}$ | 29.72 | 19.38 | 10.90 | 10.20 |

$-1.5$$\mathrm{m}$ | 33.23 | 22.59 | 11.55 | 11.00 |

$0.0$$\mathrm{m}$ | 40.42 | 27.04 | 13.55 | 12.10 |

$1.5$$\mathrm{m}$ | 41.50 | 25.45 | 15.75 | 13.80 |

Low Beam fully switched on | ||||

30 $\mathrm{m}$ | 45 $\mathrm{m}$ | 55 $\mathrm{m}$ | 65 $\mathrm{m}$ | |

$-3.0$$\mathrm{m}$ | 67.73 | 25.64 | 15.31 | 8.80 |

$-1.5$$\mathrm{m}$ | 135.30 | 27.81 | 18.94 | 9.21 |

$0.0$$\mathrm{m}$ | 94.41 | 28.66 | 15.18 | 6.84 |

$1.5$$\mathrm{m}$ | 74.88 | 26.01 | 17.38 | 10.04 |

Low Beam off | ||||

20 $\mathrm{m}$ | 35 $\mathrm{m}$ | 45 $\mathrm{m}$ | 55 $\mathrm{m}$ | |

$-3.0$$\mathrm{m}$ | 35.55 | 25.72 | 14.26 | 13.59 |

$-1.5$$\mathrm{m}$ | 40.44 | 28.85 | 14.88 | 13.81 |

$0.0$$\mathrm{m}$ | 48.72 | 33.94 | 13.56 | 17.05 |

$1.5$$\mathrm{m}$ | 51.41 | 35.78 | 18.84 | 18.91 |

Low Beam fully switched on | ||||

20 $\mathrm{m}$ | 35 $\mathrm{m}$ | 45 $\mathrm{m}$ | 55 $\mathrm{m}$ | |

$-3.0$$\mathrm{m}$ | 56.08 | 33.68 | 15.98 | 8.89 |

$-1.5$$\mathrm{m}$ | 169.47 | 38.68 | 19.74 | 8.77 |

$0.0$$\mathrm{m}$ | 151.08 | 28.92 | 21.36 | 4.95 |

$1.5$$\mathrm{m}$ | 95.21 | 23.50 | 19.70 | 2.58 |

Low Beam off | |||

Test Road | p > 90% | p > 75% | p > 50% |

1 | 15/16 | 16/16 | 16/16 |

2 | 12/16 | 15/16 | 15/16 |

3 | 14/16 | 16/16 | 16/16 |

Low Beam fully switched on | |||

Test Road | p > 90% | p > 75% | p > 50% |

1 | 6/16 | 7/16 | 12/16 |

2 | 10/16 | 11/16 | 13/16 |

3 | 12/16 | 14/16 | 15/16 |

Low Beam off | |||

Test Road | p > 90% | p > 75% | p > 50% |

1 | 16/16 | 16/16 | 16/16 |

2 | 13/16 | 15/16 | 15/16 |

3 | 14/16 | 16/16 | 16/16 |

Low Beam fully switched on | |||

Test Road | p > 90% | p > 75% | p > 50% |

1 | 12/16 | 13/16 | 16/16 |

2 | 13/16 | 15/16 | 15/16 |

3 | 15/16 | 16/16 | 16/16 |

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## Share and Cite

**MDPI and ACS Style**

Erkan, A.; Hoffmann, D.; Singer, T.; Schikowski, J.M.; Kunst, K.; Peier, M.A.; Khanh, T.Q.
Influence of Headlight Level on Object Detection in Urban Traffic at Night. *Appl. Sci.* **2023**, *13*, 2668.
https://doi.org/10.3390/app13042668

**AMA Style**

Erkan A, Hoffmann D, Singer T, Schikowski JM, Kunst K, Peier MA, Khanh TQ.
Influence of Headlight Level on Object Detection in Urban Traffic at Night. *Applied Sciences*. 2023; 13(4):2668.
https://doi.org/10.3390/app13042668

**Chicago/Turabian Style**

Erkan, Anil, David Hoffmann, Timo Singer, Julia Maria Schikowski, Korbinian Kunst, Markus Alexander Peier, and Tran Quoc Khanh.
2023. "Influence of Headlight Level on Object Detection in Urban Traffic at Night" *Applied Sciences* 13, no. 4: 2668.
https://doi.org/10.3390/app13042668