Abstract
BackgroundAlthough evidence of both beneficial and adverse biological effects of lighting has accumulated, biologically favorable lighting often does not match subjectively comfortable lighting. By controlling the correlated color temperature (CCT) of ambient lights, we investigated the feasibility of combined lighting that meets both biological requirements and subjective comfort.MethodsTwo types of combined lightings were compared; one consisted of a high-CCT (12000 K) light-emitting diode (LED) panel as the ambient light and a low-CCT (5000 K) LED stand light as the task light (high-low combined lighting), and the other consisted of a low-CCT (4500 K) LED panel as the ambient light and the same low-CCT (5000 K) stand light as the task light (low-low combined lighting) as control. Ten healthy subjects (5 young and 5 elderly) were exposed to the two types of lighting on separate days. Autonomic function by heart rate variability, psychomotor performances, and subjective comfort were compared.ResultsBoth at sitting rest and during psychomotor workload, heart rate was higher and the parasympathetic index of heart rate variability was lower under the high-low combined lighting than the low-low combined lighting in both young and elderly subject groups. Increased psychomotor alertness in the elderly and improved sustainability of concentration work performance in both age groups were also observed under the high-low combined lighting. However, no significant difference was observed in the visual-analog-scale assessment of subjective comfort between the two types of lightings.ConclusionsHigh-CCT ambient lighting, even when used in combination with low-CCT task lighting, could increase autonomic and psychomotor arousal levels without compromising subjective comfort. This finding suggests the feasibility of independent control of ambient and task lighting as a way to achieve both biological function regulation and subjective comfort.
Highlights
Evidence of both beneficial and adverse biological effects of lighting has accumulated, biologically favorable lighting often does not match subjectively comfortable lighting
We examined the possibility of combined lighting consisting of high-correlated color temperature (CCT) ambient lighting and low-CCT task lighting as a method to meet the biological requirements and subjective comfort
Significant main effects of lighting type were observed on heart rate (P = 0.01), high frequency (HF) amplitude (P = 0.0001), and low frequency (LF)/HF (P = 0.01), there was a significant interaction between lighting type and age on HF amplitude (P = 0.0002)
Summary
Evidence of both beneficial and adverse biological effects of lighting has accumulated, biologically favorable lighting often does not match subjectively comfortable lighting. By controlling the correlated color temperature (CCT) of ambient lights, we investigated the feasibility of combined lighting that meets both biological requirements and subjective comfort. The non-image forming effects of blue light include important biological regulations, such as increased vigilance [18, 19], autonomic nervous arousal [20, 21], and circadian clock adaptation to the environment [22,23,24,25], but that is why excessive exposure to blue light, especially before bedtime, could adversely affect sleep due to improper arousal and circadian rhythm disturbances [26,27,28,29,30]. Biologically required lighting characteristics often do not match subjectively comfortable lightings or those required for the activities of individual people
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