The effect of colored light in the vehicle interior on the thermal comfort and thermal responses of vehicle occupants
Authors: Bähr Sabina , Edel Fabian 
Published: June 2023

Light and colors have an impact on the mood of car drivers through their emotional change. This result was shown in our last year AHFE-Publication (2022) “Enhanced driver’s experience through emotion sensitive lighting interaction”. The result is that light and color can change the driver’s emotions to the positive and negative. This effect can have lots of further automotive application fields, e. g. the change of the drivers thermal sensation. In case of the e-mobility, warming light and color (red end of the visible spectrum) can support the heating system to get thermal comfort to the driver and will reduce energy for heating and for that increase the electric range. The thermal comfort is very important factor for driving comfort. This work aims to investigate the subjective thermal perception and physiological responses of vehicle occupants through the influence of thermal and visual stimuli in the vehicle interior. To achieve the described goal, a methodological approach was developed. The steps of the methodological approach and the research structure are shown below:•Definition of the research questions; the main question is whether colored light can influence the subjective perception of warmth and the physiology of vehicle occupants through static and dynamic lighting•Obtaining a literature review on the main topics: “thermal comfort”, “lighting in the vehicle interior” and “the influence of colored light on thermal sensation”•Derivation of requirements for the vehicle test setup•Realization of the experimental setup•Conducting a subject study•Evaluation of the data.Study design: A 4 x 2 factorial within subject design is used to determine the influence of “colored light” and “temperature” on thermal, visual, and overall comfort. Of the four scenarios of the predictor variable colored light, three are static and one is dynamic. The static light colors are blue, white, and orange and the dynamic light scenario is a video with candlelight or a video with a winter landscape depending on the temperature level. The two selected temperature levels are 24.5 °C and 26.0 °C. These were regulated via a self-built climate chamber and checked via several sensors. Since the study was conducted in summer, the temperatures were selected to be within (24.5 °C) and outside the comfortable temperature range for the vehicle interior, based on the recommendation of the German automobile association ADAC. Outcome Variables: After experiencing each colored light in combination with temperature, participants answered questions about their thermal, visual, and overall comfort of the vehicle interior environment. To check whether the colored light influences the physiology of participants, heart rate and skin temperature were continuously recorded via a wristband. Sample: Twelve valid subjects (six females, six males) participated in the vehicle lighting study, recruited without financial incentives through the University of Stuttgart and Fraunhofer IAO departments. Procedure: The combination of the predictor variables "colored light" and “temperature” resulted in eight sessions, which were all experienced by the subjects and randomized across the sessions. At the beginning of the study, the subjects received initial instructions and put on the wristband so that the recording of physiological data could start. They then entered the vehicle, and a 13-minute acclimation period began, which served to acclimate the subject to the temperature and to achieve a similar level of activity among the participants. The vehicle was then illuminated with the first color (blue or orange) for 6.5 minutes, and participants were asked to answer questions about the first session after the first four minutes. After that, the light color changed to white for one minute, and then the vehicle was illuminated with the next color. After the first four sessions at the first temperature level, there was a 15-minute break, after which the next four sessions began at the second temperature level. In total, the study lasted approximately 2 hours per participant. Analysis: Is performed using parametric and nonparametric tests. In addition, the covariates age, gender, and BMI of the subject and the temperature difference of the actual to the target temperature were examined for the influence on the outcome variables. The results show that colored light affects thermal perception under different temperature levels. The indoor environment under the orange light was perceived as warmer than under the blue light. In addition, participants found the blue light more comfortable than the orange light in warm environments and they preferred a lower temperature with orange light compared to the blue light or the dynamic video of a winter landscape in warm environments. The use of colored light could therefore lead to energy saving in the e-mobility. The full paper and presentation will go into more detail about the methodology and the results.