# The association between emotional arousal and color lightness of facial digital expressions of social robots

## TL;DR

This paper shows that changing the lightness of a robot's facial colors can influence how intense emotions appear to humans.

## Contribution

The study introduces the novel idea that color lightness alone can modulate emotional arousal in robot facial expressions.

## Key findings

- Manipulating color lightness significantly affects perceived emotional arousal in robot faces.
- Adjusting lightness can make robot emotions appear more realistic and intuitive to humans.

## Abstract

In human–robot social interactions, a robot’s facial expressions serve as a crucial channel for conveying emotions and fostering trust. However, current social robots predominantly employ emoji-like icons and simulated muscle movements for anthropomorphic ex-pression, and research on facial color–emotion relationships tends to adjust hue, saturation, and lightness simultaneously—overlooking how color lightness alone influences emotional intensity. This study explores the specific link between emotion type and color lightness in social robots’ digital facial expressions to enhance affective communication in human–computer interaction. In our experiment, participants viewed robot faces dis-playing the same emotion at varying lightness levels and rated perceived arousal on a 1–5 scale. The results confirm that manipulating color lightness significantly modulates emotional arousal. Overall, these findings suggest that adaptive lightness adjustments in robot facial colors can yield more realistic and intuitive affective interactions between humans and machines.