## 4 Color and Light in Affective Computing
### Color and Light as Affective Factors
#### 4.2.2 Influence of Color in Affective Computing  
Color is always present in our visual environment. Humans live consonant with their color choices that usually correspond to their internal rational and irrational feelings. Color preferences can be individual, collective and universal. Personal preferences correspond to the person's character as well as his/her moods and emotions. The evidences of color influence upon emotions have been discussed in a number of publications. Here we introduce some of the most relevant. [PERSON] _et al._[57] show that plants are sensitive to the color of the light under which they are grown. The effect is maximal for red-enriched illumination. [PERSON] _et al._[58] demonstrate that a brief exposure to red prior to a test unconsciously enhances the performance of the participants. Moreover, a link between red and avoidance motivation is discovered. The authors suggest that the red color influences behavior considerably; and care must be taken when using it in performance and achievement contexts. Some authors indicate antimicrobial and insecticide properties of blue color and light, reminding the tradition of painting houses and doors in blue in southern countries in order to get rid of insects [51]. In this context, it is worth mentioning an experiment which aimed to examine the possibility of enhancing antibody concentration and alleviate stress response in broilers. The experiment concludes in exposing broilers to white, red, green and blue light [59]. The results suggest that the combination of green and blue monochromatic light improves the broilers' immune function. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Reference** & **Emotion(s)** & **Color Description Model and Color Sample** \\ \hline [PERSON] _et al._[60] & Semantic scales warm/cool, heavy/light, active/passive, and like/dislike & Two-color model, CIELAB; 190 color pairs \\ \hline [PERSON] _et al._[38] & 12 emotion variables (word pairs) & Munsell color system, SCOTDIC PLUS 2000 system; 214 color samples \\ \hline [PERSON] [61] & Semantic word pairs “bright-dark” (activity factor), “like-dislike” (evaluation factor) and “strong-weak” (potency factor) & 2 datasets with different stimuli and scales; 27 color pairs, composed of eight colors (red, blue, green, yellow, orange, cyan, magenta, and violet); luminances and CIE xy color coordinates \\ \hline [PERSON] _et al._[62] & Attributes associated with emotional responses & Brightness level (light, medium, dark) and nine hues (red; orange; yellow/orange; yellow; green; blue/green; blue; purple; and white/gray/black) \\ \hline [PERSON] _et al._[63] & Heart rate variability (HRV) & Blue, red and white colored fluorescent lights \\ \hline [PERSON] _et al._[37] & Color emotions described in 12 opponent word pairs & SCOTDIC PLUS 2000 system, Munsell color system; 218 color samples \\ \hline [PERSON] _et al._[32] & 12 emotion variables (word pairs) & Working environments with no color at all; with neutral colors; with not very vivid color; very colorful and vivid \\ \hline [PERSON] and [PERSON] [64] & Three emotion factors: activity, weight, and heat & RGB space; 567 samples \\ \hline [PERSON] _et al._[41] & Color emotion based on the analysis of color preference questionnaires & Self-created color space, where value and chroma are controlled, and hue parameter are changed with a constant physical difference in hue of 20 grades, with addition of black and white, totally 23 home page color schemes \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Color in visual affect recognition. Color's effect on emotional state can be measured indirectly by means of affective semantic words and word combinations. Table 1 contains references to many studies which are based on this approach. An analysis of this table reveals some common trends in the organization of experiments on color emotion. First, an indirect emotion assessment is widely used. It means that an emotion is evaluated with semantic words.