Long-Term Blue Light Exposure Changes Frontal and Occipital Cerebral Hemodynamics: Not All Subjects React the Same

In modern society, we are increasingly exposed to numerous sources of blue light, including screens (e.g., TVs, computers, laptops, smartphones, tablets) and light from fluorescent and LED lamps. Due to this wide range of applications, the effects of blue light exposure (BLE) on the human physiology need to be thoroughly studied.

To investigate the impact of long-term BLE on frontal and occipital human cerebral hemodynamics and oxygenation using functional near-infrared spectroscopy (fNIRS) neuroimaging.

32 healthy right-handed subjects (20 females, 12 males; age: 23.8 ± 2.2 years) were exposed to blue LED light for 15 minutes. Before (baseline, 8 min) and after (recovery, 10 min) the BLE, subjects were in darkness. We measured the concentration changes of oxyhemoglobin ([O₂Hb]) and deoxyhemoglobin ([HHb]) at the prefrontal cortex (PFC) and visual cortex (VC) by fNIRS during the experiment. Subjects were then classified into different groups based on their hemodynamic response pattern of [O₂Hb] at the PFC and VC during BLE.

On the group level (32 subjects), we found an increase in [O₂Hb] and a decrease in [HHb] at both cortices during BLE. Evoked changes of [O₂Hb] were higher at the VC compared to the PFC. Eight different hemodynamic response patterns were detected in the subgroup analysis, while an increase of [O₂Hb] in both cortices was the most common pattern (8 out of 32 cases, 25%) during BLE.

Our study showed that the hemodynamic and oxygenation changes at the PFC and VC during BLE (i) were generally higher in the VC compared to the PFC, (ii) showed an intersubject variability with respect to their magnitudes and shapes, and (iii) can be classified into eight groups. We conclude that blue light affects humans differently. It is essential to consider this when assessing the impact of the BLE on society.