Relative Evaluation of Comfort Level Associated with Light-Emitting Diode Lighting Based on near Infrared Spectroscopy

Abstract

Although the use of light-emitting diode (LED) lighting has rapidly become popular as the next-generation of lighting, the degree of comfort associated with these lights has not been sufficiently examined. Therefore, establishing both subjective and objective evaluation methods to test the comfort associated with LED lightings is desirable. We investigated the comfort associated with LED lighting by using near infrared (NIR) spectroscopy. The study recruited 35 healthy young adults with no ophthalmological diseases. Three types of lighting, including edge-lit LED, direct-lit LED and fluorescent lighting, were used for the subjective evaluation and measurements of the brain function in both Experiment 1 (comfort verification of lighting illuminance) and Experiment 2 (comfort verification of lighting type). Brain measurements were performed using an NIR sensor and by assessing the oxygenated haemoglobin concentration changes in the frontal lobe during the time the subjects looked at each type of light. The subjective evaluation determined that lighting luminance at 800 lux significantly lowered the comfort level, while direct-lit LED and fluorescent lighting significantly lowered the comfort level as compared with edge-lit LED lighting. Lighting illuminance of 800 lux induced a significant increase in oxygenated haemoglobin concentration compared with the control conditions when eyelids were closed. In addition, looking at direct-LED and fluorescent lighting significantly increased oxygenated haemoglobin concentration compared with edge-lit LED lighting. Our study suggests that the subjective comfort level experienced while looking at different types of lighting could potentially be evaluated based on changes in oxygenated haemoglobin concentration within the frontal lobe detected using NIR sensors.