Enhancement of autonomic and psychomotor arousal by exposures to blue wavelength light: importance of both absolute and relative contents of melanopic component

Abstract

Background: Blue light containing rich melanopsin-stimulating (melanopic) component has been reported to enhance arousal level, but it is unclear whether the determinant of the effects is the absolute or relative content of melanopic component. We compared the autonomic and psychomotor arousal effects of melanopic-enriched blue light of organic light-emitting diode (OLED) with those of OLED lights with lesser absolute amount of melanopic component (green light) and with greater absolute but lesser relative content (white light).

Methods: Using a ceiling light consisting of 120 panels (55 × 55 mm square) of OLED modules with adjustable color and brightness, we examined the effects of blue, green, and white lights (melanopic photon flux densities, 0.23, 0.14, and 0.38 μmol/m²/s and its relative content ratios, 72, 17, and 14%, respectively) on heart rate variability (HRV) during exposures and on the performance of psychomotor vigilance test (PVT) after exposures in ten healthy subjects with normal color vision. For each of the three colors, five consecutive 10-min sessions of light exposures were performed in the supine position, interleaved by four 10-min intervals during which 5-min PVT was performed under usual fluorescent light in sitting position. Low-frequency (LF, 0.04-0.15 Hz) and high-frequency (HF, 0.15-0.40 Hz) power and LF-to-HF ratio (LF/HF) of HRV during light exposures and reaction time (RT) and minor lapse (RT >500 ms) of PVT were analyzed.

Results: Heart rate was higher and the HF power reflecting autonomic resting was lower during exposures to the blue light than the green and white lights, while LF/HF did not differ significantly. Also, the number of minor lapse and the variation of reaction time reflecting decreased vigilance were lower after exposures to the blue light than the green light.

Conclusions: The effects of blue OLED light for maintaining autonomic and psychomotor arousal levels depend on both absolute and relative contents of melanopic component in the light.

Keywords: Arousal; Blue light; Heart rate variability; Intrinsically photosensitive retinal ganglion cell; Melanopic component; Melanopsin; Non-image forming vision; Organic light-emitting diode; Psychomotor vigilance.

Fig. 1

Ceiling light device with organic light-emitting diode (OLED). The device consists of 120 OLED panels (VELVE OLED lighting module with adjustable red-green-blue color and brightness, 55 × 55 mm square, Mitsubishi Chemical Pioneer OLED Lighting Corporation, Tokyo, Japan) that are aligned in a 10 × 12 reticular pattern

Fig. 2

Photon flux density (PFD) spectra of colored OLED lights and relative papillary area measured during exposure to these lights in the supplementary study. a PFD spectra of blue, green, and white lights measured at the place of the eyes of subjects lying on a bed right under the ceiling light. b Average relative pupillary area measured during exposure to the lights in seven subjects in the supplementary study. Error bars indicate the range of ± SD of relative diameters. c Estimated PFD spectra of lights reaching the retina calculated from the relative pupillary areas during exposure to the lights. d Melanopic spectral efficiency curve adjusted for human pre-receptoral filtering generated from the data in reference [13]. Vertical dashed lines in both panels indicate the position of λ _max of the adjusted melanoptic spectral efficiency (490 nm). e Estimated MSPFD spectra of lights reaching the retina calculated from the relative pupillary areas during exposure to the lights

Fig. 3

Experimental protocol of the main study. The series of OLED light exposure sessions with blue, green, and white lights were performed in all subjects with orders counterbalanced across subjects

Fig. 4

Mean heart rate and heart rate variability indices during five sessions of blue, green, and white light exposures in ten subjects in the main study. Error bars indicate standard error of the means. HF high-frequency component, LF low-frequency component, LF/HF LF-to-HF ratio in power

Fig. 5

Transformed minor lapses, slowest and fastest tenth percentile reaction times (RT), and fastest-slowest RT difference during four sessions of psychomotor vigilance test (PVT) after blue, green, and white light exposures in ten subjects in the main study. Error bars indicate standard error of the means