"INVESTIGATING THE INFLUENCE OF SPECTRAL POWER DISTRIBUTION CHARACTERISTICS ON HUE DIFFERENTIATION TASK PERFORMANCE"
This thesis investigates the effects of spectral power distribution (SPD) characteristics of light sources on the hue differentiation performance of observers. Color differentiation efficiency of light sources was investigated with respect to their SPD characteristics. Hue attribute of Kürkçü’s (2017) differentiation task was used in this study. Three different groups of students performed the hue differentiation task under 3 different lighting settings; D65, Light Emitting Diode (LED), and Compact Fluorescent Light (CFL) with 4000K and 6500K Correlated Color Temperatures (CCT). The speed and accuracy of performing the hue differentiation task were investigated to indicate the task performance. Ninety students from different departments at Bilkent University and Middle East Technical University voluntarily participated in this study. The participants performed the hue differentiation task inside a light booth as a control light condition. Additionally, the alertness level of the participants as a biological effect of light sources was also investigated in this study. The alertness level of participants was assessed using Karolinska Sleepiness Scale (KSS). The results showed that the SPD characteristic of the light sources was effective on the hue differentiation performance of observers. Indeed, the hue differentiation performance was in proportion to the radiation intensity of the SPDs of light sources. Overall accuracy and speed of D65 were significantly better in pairwise comparison with LED and CFL due to wide and continuous band SPD characteristics. Moreover, under LED light source the accuracy of the Green to Blue (G to B) hue differentiation task was lower in comparison to other hue tasks. However, under CFL the accuracy of the Red to Yellow (R to Y) hue differentiation task was lower in comparison to other hue tasks. It was found that the alertness level and perceived performance of the participants were not significantly different under different light sources.