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.