Blue Light is Not More Efficient than White Light
for Light Therapy
Harvard Confirms Lack of Benefit from Blue Light
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).
The Risk to Vision from Blue Light
Cumulative blue light exposure over a lifetime contributes to the development of Age-related Macular Degeneration (AMD), the leading cause of blindness in the developed world. Blue light wavelengths do not contribute to the effectiveness of light therapy. Therefore, the use of blue or blue-enhanced light therapy lamps only increases the risk of retinal damage and vision loss, without providing any benefit.
While green light with wavelengths near 555 nm used in the study described above is
not very effective for light therapy, 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 confirmed is the most sensitive region of the spectrum for regulating
human circadian rhythms.
The finding that blue light wavelengths do not increase the effectiveness of light therapy, contrast with studies using Lo-LIGHT lamps for the treatment of depression, regulating circadian phase, and on light induced melatonin suppression, which show that GreenLIGHT from a Lo-LIGHT therapy lamp is as effective as "bright" white light therapy that provides more than 20 times the intensity or brightness.
Unlike bright light or blue light therapy lamps, the Lo-LIGHT therapy lamp poses no risk to the user's vision. (MORE on Light Therapy and Retinal Damage)
Misunderstandings used to Justify using Blue Light in Light Therapy.
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 a 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
Research supporting the superiority of GreenLIGHT to blue light for light therapy.
GreenLIGHT Provides Most Efficient Wavelengths for LIGHT Therapy
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