Fatigue evaluation of colored LED backlit text based on prefrontal cortex activity measurement by Near-Infrared Spectroscopy

This study aims to examine the benefit of visual fatigue evaluation based on prefrontal cortex (PFC) measurement by near infrared spectroscopy (NIRS), and to evaluate fatigue on various colored LED backlit text. In our method, eight adult participants read a LED backlit text 10 minutes in a dark room. Before and after task, subjective fatigue questionnaire “Jikaku-sho shirabe”, subjective visual fatigue questionnaire (SVF), and the critical flicker-fusion frequency (CFF) were measured. The time-course of oxy-Hb in the PFC was measured using a 22-channel NIRS. Heart rate variability (HRV) was measured to access an autonomic nervous system balance. Six types of white LEDs were used for backlighting: general white as a control (W), high color-rendering white (WH), bluish white (WB), reddish white (WR), greenish white (WG), and yellowish white (WY). In our results, correlation analysis suggested that the development of central fatigue is related to deactivated condition in the mPFC, and the development of subjective visual fatigue is related to deactivated condition in the LPFC. In comparison between LED treatments, in WH condition, high subjective central fatigue, CFF decay and LF/HF were revealed, and the PFC inactivated. In WG condition, low subjective central fatigue and CFF decay revealed. Our findings suggested that participants get tired on high color-rendering white LED backlit text, and were less tired in greenish white LED backlit text. Also, NIRS provides benefits in the evaluation of visual fatigue.