Lighting for pedestrians:
Looking at other people

Using mobile eye tracking to record the visual fixations suggested that looking towards other people is an important visual task.

This may be to evaluate their intentions and decide whether to approach or avoid.

Fotios S, Uttley J, Cheal C, Hara N. Using eye-tracking to identify pedestrians’ critical visual tasks. Part 1. Dual task approach. Lighting Research and Technology, 2015; 47(2); 133-148.

The eye tracking records were analysed to find out how we tend to look at other people.

This suggested a tendency to look at other people when they are approximately 15 m away and for only 0.5 seconds.

These are critical data for lighting experiments. The distance away tells us about the visual size of the target: past studies using a assumed 4 m distance or using a stop-distance procedure may have drawn incorrect conclusions. The duration tells us about task difficulty: past studies allowing unlimited observation of the target person provide an easier task and therefore an underestimate of the lighting needed.

Fotios S, Uttley J, Fox S. Exploring the nature of visual fixations on other pedestrians. Lighting Research and Technology 2018; 50(4): 511-521.

Past studies have tended to focus on facial identity recognition. We suspected that was not the best approach to take. First, we are able to recognise identity easily, even under difficult visual conditions. Second, there was a tendency to use continuous observation of the target face, which is not the natural way of looking at other people.

In this work, with Yandan Lin of Fudan University, it was shown that conclusions drawn about lamp type and facial identification are affected by choice of procedure and observation time.

These issues were not considered in past studies.

Lin Y, Fotios S. Investigating methods for measuring facial recognition under different road lighting conditions. Lighting Research and Technology, 2015; 47(2); 221-235.

The effect of procedure and duration was explored in further work with Yandan Lin.

This work suggested a possible measure for task difficulty, the product of luminance and duration, and this provided a good fit to the experimental results.

Dong M, Fotios S, Lin Y. The Influence of Observation Duration and Procedure on Luminance Required for Recognition of Pedestrian’ Faces. Lighting Research and Technology, 2015; 47(6); 693-704.

If facial identity recognition is not the right task, what is? In this review with Maria Johansson of Lund University, it was suggested that we should instead consider facial emotion recognition.

This is advantageous in many ways. (1) Emotion can be assessed using facial expressions using a discrimination procedure: this is a more precise and objective task than celebrity naming. (2) There is no need to use celebrity faces; there are validated databases of actors portraying the universally recognised facial expressions – happy, fearful, angry, neutral etc.

This is not a proposal that the main task of a pedestrian is to judge a person’s facial expression, but instead that it is a suitable representative task for what a pedestrian’s visual task.

Fotios S, Johansson M. Appraising the intention of other people: Ecological validity and procedures for investigating effects of lighting for pedestrians. Lighting Research and Technology 2019; 51(1): 111-130.

We carried out three experiments to examine how changes in luminance and lamp spectrum would affect facial emotion recognition.

In this first experiment, three targets were used: facial expression, body posture, and gaze direction.

Previous studies (on facial identity recognition) have produced mixed results about the effect of lamp spectrum, some suggesting a significant effect while others suggesting no effect.

The results of this experiment did not suggest an effect of lamp spectrum. This may be because facial expression discrimination is a foveal task, or it may be because the experimental design was sufficient to reveal an effect.

Fotios S, Yang B, Cheal C. Effects of Outdoor Lighting on Judgements of Emotion and Gaze Direction. Lighting Research and Technology, 2015; 47(3); 301-315.

In the second experiment we used only facial expressions, but extend the number of levels of luminance in order to better draw the performance versus luminance graph.

We also added an additional lamp spectrum.

Again, these results did not reveal an effect of lamp spectrum.

Yang B, Fotios S. Lighting and Recognition of Emotion Conveyed by Facial Expressions. Lighting Research and Technology, 2015; 47(8); 964-975.

In the third experiment we changed the experimental design to increase the likelihood of revealing an effect of lamp spectrum on facial emotion recognition. This included the use of both coloured and achromatic targets. We also presented the targets using a data projector, which provided images of better clarity than the non-self-luminous screen used in the previous experiments.

Again, these results did not reveal an effect of lamp spectrum.

Fotios S, Castleton H, Cheal C, Yang B. Investigating the chromatic contribution to recognition of facial expression. Lighting Research and Technology, 2017; 49(2); 243-258.

Reviewers of the three experiments had asked whether the results were influenced by the choice of facial expression.

We therefore re-analysed the data but for each expression separately rather than across all expressions combined.

This did not change the conclusions.

Fotios S, Castleton H, Yang B. Does expression choice affect the analysis of light spectrum and facial emotion recognition? Lighting Research and Technology 2018; 50(2): 294-302.

In typical experiments investigating facial emotion recognition (FER), FER is the only task of concern for the test participant. That does not reflect the natural situation. In this experiment we explored the influence of multi-tasking, the effect on task performance of conducting two tasks within the same session.

Mao Y, Fotios S. Lighting for pedestrians: Does multi-tasking affect the optimal light level determined using task performance? Lighting Research and Technology 2022; 54(1): 33-60.

Ongoing work

The current data do not suggest that the approach-avoid decision is influenced by lamp spectrum.

In current work we are using 3D target faces, and investigating the influence of lighting direction and glare.