A Harvard university study published in a Science journal confirms that increasing the proportion of blue light wavelengths emitted from a light therapy lamp has no benefit and does not improve effectiveness or efficiency. The editorial comment accompanying the article proposes that "blue light now often used for therapy in depression or shift work should perhaps be replaced by green or white illumination."1
"Our results indicate that short-duration (<90 min) retinal exposure to narrow-bandwidth 555-nm [yellow-green] light may be as effective, if not more effective, than an equivalent photon dose of 460-nm [blue] light."2 Since green light with wavelengths around 555 nm are not very effective for light therapy, and since light therapy is generally used for less than 60 minutes, there would be no benefit in the use of blue light, or in increasing the proportion of blue light wavelengths in a light source used for light therapy.
[Science Translational Medicine is the American Association for the Advancement of Science journal directed toward the implementation of scientific research into the practice of medicine]
The subjects used in this study were under 30 years of age, which is meaningful because studies have shown there is a substantial decrease in the efficacy of blue light therapy in people over 40 years old. This results from the age-related yellowing of the lens which increasingly and substantially limits the amount of blue light reaching the retina after age 40.
While this result has also been found in several other studies, the authors of this study include many researchers whose earlier publications are used to justify using blue light or increasing the proportion of blue light to improve the efficiency of light therapy lamps. (e.g. GC Brainard, CA Czeisler, SW Lockley etc).
It is now becoming evident that cumulative blue light exposure contributes to the development of Age-related Macular Degeneration (AMD), the leading cause of blindness in the developed world. As blue light wavelengths are not beneficial for light therapy, the use of blue or blue-enhanced light therapy lamps can only increase the risk of vision loss, without any offsetting potential benefit.
While green light with wavelengths near 555 nm used in the study described above has been shown to be not very effective for light therapy by several research groups, Lo-LIGHT lamps emit a narrow range of green light peaking in the visible light spectral region of 500 to 505 nm, which researchers at Harvard determined is the most sensitive region of the spectrum for the human circadian system. In contrast to the finding that blue light wavelengths do not increase the effectiveness of light therapy, several studies on light therapy regarding the treatment of depression, regulating circadian phase, and on light induced melatonin suppression demonstrate that GreenLIGHT from a Lo-LIGHT therapy lamp is as effective as "bright" white light therapy that provides more than 10 times the intensity or brightness. Unlike bright light or blue light therapy lamps, the low intensity green light from a Lo-LIGHT therapy lamp poses no risk to the user's vision. (MORE on Light Therapy and Retinal Damage)
The theoretical understanding on which blue light therapy was based, i.e. that the absorption spectrum of melanopsin in intrinsically photosensitive ganglion cells in the mammalian retina determines the spectral sensitivity of the photic pathway from the retina to light sensitve regions of the brain not involved in vision, was ill-conceived. As the authors of a recent paper in Neuron stated, "our data suggest a relatively simple segregation of photoreceptor inputs to NIF [nonimage forming] vision under field conditions. They predict that rods play the predominant role in driving responses at night and around dawn/dusk with melanopsin taking over throughout most daylight."3
Altimus et al. found "At low light intensity, ipRGCs lack sensitivity, whereas rods are known to respond to increasing light levels and thus reliably relay this information to higher centers. Rods will continue to signal persistent light exposure through the rod-cone pathway even under conditions where their photocurrent is saturated. Finally, at high light intensities and for prolonged light exposures, melanopsin phototransduction in ipRGCs will extend the range of light intensities that allow circadian photoentrainment." 4 It is now apparent that the wavelength sensitivity of human physiology to light exposure does not simply correspond to the spectral excitation sensitivity of melanopsin. These finding support Sunnex Biotechnologies earlier studies on the spectral sensitivity of the non-visual light response in humans, and help explain the effectiveness of the patented low intensity GreenLIGHT technology used in Lo-LIGHT lamps.
1 CHRIS BICKEL/SCIENCE TRANSLATIONAL MEDICINE
2 Spectral Responses of the Human Circadian System Depend on the Irradiance and Duration of Exposure to Light. Science Translational Medicine
3 Distinct Contributions of Rod, Cone, and Melanopsin Photoreceptors to Encoding Irradiance. Neuron 66:417-428. Lall, Lucas et al
4 Rod Photoreceptors Drive Circadian Photoentrainment across a Wide Range of Light Intensities. Nature Neuroscience; Altimus, Hatar et al
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