## 4 Color and Light in Affective Computing
### Color and Light as Affective Factors
#### 4.2.2 Influence of Color in Affective Computing
They usually include, but are not limited to, the following pairs: \"warm/cold\", \"heavy/light\", \"like/dislike\", and \"soft/hard\". Not many studies presented in Table 1 use physiological sensors for color-based emotion evaluation. For example, [PERSON] _et al._[63] receive information about heart rate variability to detect an emotion. Factor and correlation analysis (e.g., [32, 38, 60, 61, 64]) and ANOVA (e.g., [32, 41, 63]) head the list of the most widely used classification methods for color-based emotion regulation. RGB histograms for measuring statistical properties of color images are calculated in Solli and Lenz [64]. [PERSON] _et al._[62] use decision tree models for classification. Firstly, results are calculated for countries based on brightness level choice. Next, they offer results for mean ranks of associations of hues given a brightness level choice. Besides ANOVA, [PERSON] _et al._[41] also performs cluster analysis for website designers to evaluate color preference. With the purpose of studying color emotion, [PERSON] [61] use factor analysis, and, in the case of failure, independent component analysis with intrinsic statistical properties of data such as kurtosis. Referring to the number of participants of the tests, some authors conduct experiments on an international level. This is the case of: [PERSON] _et al._[60], where 223 participants from 8 countries are interviewed; [PERSON] _et al._[38], where the sample includes people from 7 different region groups; and [PERSON] _et al._[37], where the sample counts with people from Japan, Thailand, and Hong Kong. The most numerous inquiries mentioned are carried out by [PERSON] _et al._[62] and [PERSON] _et al._[32], which count with 2021 subjects from Brazil, Canada, China, France, Germany, India, Italy, Japan, South Korea, Spain, the United Kingdom and the United States, and with 998 persons aged 18 to 65 years from Argentina, Saudi Arabia, Sweden and the UK. Nevertheless, other references report about shorter groups of participants, such as the one which consisted of 36 undergraduate or graduate students [61], 92 adult volunteers [63], and 52 observers in the pilot and 35 in the main study [64]. Affective modulation by means of color may be performed in accordance with the metamodel shown in Figure 5. Here, color influence produces emotional changes, which are reflected in the human face. They can also alter some voice characteristics as well as causing bodily changes [65, 66]. In case wearable sensors are used, physiological indicators of changes in emotional state (skin temperature, electrodermal activity, skin impedance, heart beat rate, _etc._) can be registered as reported in numerous studies (e.g., [67, 68, 69]). However, a considerable number of findings indicate that the visual channel is dominant for affective stimuli perception as well as for emotional state \"reading\" through visually detectable indicators [67, 70]. Thus, the combination of the many possible indicators of emotion expression and experience facilitate the identification of the affective status. Figure 5 suggests a possibility of a feedback with the aim of affective regulation by changing color and/or light. It is important to note that some findings demonstrate that color features like chroma, hue or lightness cause an impact on emotions [25,37,71]. Indeed, it has been proved that the chromatic palette contains emotionally charged information as opposed to the achromatic one [25]. Lightness and chroma (though the degree of its influence is small in some cases) of color appear to dominate on most of the color emotion pairs in the research reported by [PERSON] _et al._[37]. Contrary to those two factors, the hue of a color does not affect the emotional state of the participants of the test. Similar results confirming the findings reported by [PERSON] _et al._[37] are obtained by [PERSON] [48]. [PERSON] _et al._[60] point that older observers show strong preference to colors with higher chroma while younger people prefer achromatic colors.