The impact of modulated, colored light on the autonomic nervous system.

CONTEXT: Scientists are now finding that light acts on individuals through multiple pathways, most notably the optic nerve that links to the brain's visual cortex, providing a pathway for the visual effects of light. The optic nerve also links to the more recently discovered retinohypothalamic tract, providing a pathway for the nonvisual effects of light. However, specific effects have not yet been widely evaluated clinically, especially in relationship to chromotherapy (ie, therapy based on colored light).

OBJECTIVE: The purpose of this study was to evaluate the impact of modulated-light projections, perceived through the eyes, on the autonomic nervous system (ANS).

DESIGN: The research team designed a randomized, controlled, partially blinded study with three intervention groups and one control group.

SETTING: The study took place in two locations: (1) Midwestern State University, Wichita Falls, Texas, USA (40 participants) and Centre de Santé Satori, Québec, Canada (77 participants).

PARTICIPANTS: The research team recruited 117 individuals, 89 women and 28 men, to participate in the study. Participants were normal healthy individuals who were 19 to 72 y old (average age = 43 y).

INTERVENTION: Three types of light projections, each containing both specific colors and specific modulations in the frequency range of brainwaves, were tested, in addition to a placebo projection consisting of nonmodulated white light.

OUTCOME MEASURES: Evaluation was done using a combination of physiological measures-heart rate (HR), heart rate variability (HRV), and skin conductance (SC)- and psychological tests: the Profile of Mood States (POMS) and a subjective evaluation questionnaire.

RESULTS: The research team observed significant differences in the effects of light-modulation projections from baseline to postsession as compared with an equivalent intensity of white light, including decreased HR, increased HRV standard deviations of normalized NN (beat-to-beat) intervals (SDNN), very low (VLF) and low frequency (LF) levels, and decreased POMS total mood disturbance (TMD). Also, the different colors of modulated light were found to result in different ANS effects.

CONCLUSIONS: Interest is growing in the therapeutic potential of light. The effects demonstrated in the current study indicate that colored light could significantly enrich the therapeutic potential of light, and further research into chromotherapy is warranted.