Effects of Changes in Colored Light on Brain and Calf Muscle Blood Concentration and Oxygenation

Abstract

Color light therapy is a therapeutic method in complementary medicine. In color therapy, light of two contrasting colors is often applied in a sequential order. The aim of this study was to investigate possible physiological effects, i.e., changes in the blood volume and oxygenation in the brain and calf muscle of healthy subjects who were exposed to red and blue light in sequential order. The hypothesis was that if a subject is first exposed to blue and then red light, the effect of the red light will be enhanced due to the contrastingly different characteristics of the two colors. The same was expected for blue light, if first exposing a subject to red and then to blue light. Twelve healthy volunteers (six male, six female) were measured twice on two different days by near-infrared spectroscopy during exposure to colored light. Two sequences of colored light were applied in a controlled, randomized, crossover design: first blue, then red, and vice versa. For the brain and muscle, the results showed no significant differences in blood volume and oxygenation between the two sequences, and a high interindividual physiological variability. Thus, the hypothesis had to be rejected. Comparing these data to results from a previous study, where subjects were exposed to blue and red light without sequential color changes, shows that the results of the current study appear to be similar to those of red light exposure. This may indicate that the exposure to red light was preponderant and thus effects of blue light were outweighed.

Effect of short-term colored-light exposure on cerebral hemodynamics and oxygenation, and systemic physiological activity

“…The response of the left PFC to a wide-field stimulation with two color sequences, i.e., 5-min blue-light exposure followed by 5-min red-light exposure, or vice versa, was studied in Ref. 59. There was no significant difference between the two sequences, even though blue/red seemed to evoke a larger response compared to red/blue.…”

“…In pioneering studies in humans using functional near-infrared spectroscopy (fNIRS), long-term blue light elicited a stronger hemodynamic response in the PFC than red light 58 . In contrast, color sequences (blue/red, red/blue) showed no significant effect 59 …”

Color-dependent changes in humans during a verbal fluency task under colored light exposure assessed by SPA-fNIRS

“…For further, more detailed information on NIRS-based techniques, we refer readers to Scholkmann et al 28 . In our previous studies, we investigated how cerebral hemodynamics and oxygenation change during different short-term and long-term colored light exposures 13 , 38 , 41 , 65 – 67 . The impact of the VFT on human brain activity and cerebral perfusion was also investigated in several fNIRS studies 68 – 71 .…”

Possible effect of natural light on emotion recognition and the prefrontal cortex: A scoping review of near-infrared (NIR) spectroscopy

“…Wolf's research group extensively focused on the color of light and conducted 8 fNIRS studies in the years 2011-2022. [70][71][72][73]77,78,82,83 In 2011, they first investigated the effect of red and blue light on oxygen consumption in the brain and muscles of 10 participants. 77 Then, they exposed the 12 volunteers to these 2-colored lights sequentially to examine the hypothesis stating that red light enhances the effects of BL.…”