Blue Light Therapy vs Green Light Therapy: Spectral Sensitivity of Light Therapy and the photic pathway to the biological clock in the brain

GreenLIGHT Therapy vs Blue Light Therapy

Definitions: The terms "blue light" and "green light" have been used by various groups to describe different regions of the visible spectrum. In this discussion we will use the terms "blue light" and "green light" according to the following definitions:
Blue Light is comprised of light wavelengths that appear blue to a the human eye, and are made up of wavelength shorter than 480 nm. This definition is also relevant to the term "blue light hazard" which describes the retinal sensitivity to photochemical stress from visible light wavelengths, which peaks at 440 nm and falls to 62% of peak by 470 nm, and 10% of peak by 500 nm. "Blue" light therapy lamps used for chronobiological interventions use wavelengths in the region from 450 nm to 479 nm
Green Light is comprised of light wavelengths that appear green or teal to the viewer, and are made up of wavelengths longer than 480 nm (and shorter than 570 nm). The GreenLIGHT technology used in Sunnex Biotechnologies Lo-LIGHT lamps is comprised of a narrow band of green wavelengths that peak near 500 nm.

Introduction.

There has been some controversy regarding the relative effectiveness of blue light wavelengths, i.e. wavelengths shorter than 480 nm, as compared with light wavelengths in the region of 500 nm as provided by Sunnex Biotechnologies GreenLIGHT technology. Some research group and manufacturers have given the impression blue light wavelengths are the most efficient and effective wavelengths for light therapy. However, after years of studies with "blue-enriched" light, it is now apparent this in not the case. (See Ref- Editorial in Sleep Med 2009) In 2007, a study at the Surrey University Chronobiology Center found that blue light monochromatic blue light (479 nm) is only about as efficient as ordinary white [polychromatic] fluorescent light in inducing a physiological response (melatonin suppression), even for young people. More recently, in 2008 and 2009, studies at Harvard Medical School and the Rush University Medical Center, were unable to demonstrate that increasing the proportion of blue wavelengths in a light source improved its effectiveness in shifting the circadian rhythms of humans. (See Ref) In contrast, LO-LIGHT lamps have been found to be as effective as white fluorescent lamps that provide more than 10 times as much intensity (irradiance).

Additionally, the human lens yellows with age, which substantially limits harmful blue light wavelengths from reaching the retina in people over forty. This is generally a positive adaptation, because the retina becomes increasingly susceptible to blue light damage with age. However, the yellowing retina limits the amount of blue light reaching the retina and reduces the efficiency of blue light or blue light enhanced therapy lamps. Studies now demonstarte that the age-related reduction of blue light transmission to the retina is associated with a corresponding age -related reduced sensitivity of chronobiological physiology to exposure to blue light wavelengths. (See Ref.) In contrast, the yellowing lens does not limit the proportional transmission of light wavelengths emitted by lamps using the GreenLIGHT technology. Therefore, unlike lamps that emit blue light wavelengths, there is no age-related reduction in comparative efficiency with Lo-LIGHT lamps, which can be used safely by people of all ages.

Spectral sensitivity of the photic pathway to the hypothalamic region of the brain

The measure of the physiological response to light exposure is determined by the extent of the induced phase shift and by the degree of supression of nocturnal melatonin levels. The ability of low intensities of GreenLIGHT from a Sunnex Biotechnologies Lo-LIGHT therapy lamp to induce the equivalent physiological response to that historically induced by high intensities of white light has been confirmed in an independent study by the Canadian Defense Department's R&D Centre and the U.S. Air Force published in July 2007.
This study, comparing the phase shifting capability of phototherapeutic devices, found that with less than 10% of the light intensity(energy), Sunnex Biotechnologies Lo-LIGHT twin tower unit was twice as effective as a device that emits primarily blue light. (the Litebook®) The GreenLIGHT technology was found to be as effective or more effective than any of the other devices tested, even though it provided only a very small fraction of the light intensity provided by the other phototherapeutic devices. The authors concluded: "The [Sunnex Biotechnololgies] light tower was the best device, producing melatonin suppression and circadian phase change while relatively free of side effects". (See Ref.).

The selection of Sunnex Biotechnologies green light emitting Lo-LIGHT lamps for use in the 2009 105-day Mars Mission by Harvard University attests to the advantages and superiority of the GreenLIGHT technology. A press release on this project by the National Space Biomedical Research Institute (NSBRI), the leader of the research group stated "Based on previous laboratory studies, we anticipate that during exposure to the shorter wavelength green light that melatonin will be significantly suppressed, resulting in better performance during overnight work." (More at)

Historical Context - A Review of Studies on Spectral Sensitivity of Light Therapy

There were four early studies (Thapan et al. J Physiol 2001; Brainard et al. J Neurosci 2001; Cooper et al. ARVO 2004; and Wright et al, J Pineal Res 2004) that assessed the non-visual spectral sensitivity of humans. The first two, Thapan and Brainard, appear to present data indicating that human spectral photic sensitivity of the non-visual centers of the brain, as measured by nocturnal serum melatonin suppression, peaks in the blue region of the visible light spectrum, at 459 nm (Thapan) and 464 nm (Brainard). However, subsequent studies found maximal spectral sensitivity of melatonin suppression and phase shifting in the green range of the visible spectrum, centered at 500 nm (Wright), or were basically flat from 460-500 nm (Cooper), extending from the long end of the visible blue region of the spectrum to the short end of the green region of the spectrum.

Not all of these studies were conducted on the same terms. A careful reading of the Thapan paper indicates that in order to determine the spectral sensitivity of the photoreceptor system, the data was "corrected" to account for "lens density changes" [yellowing] in such a way that does not apply to light therapy, since the spectral sensitivity of a light therapy user is affected by the absorption of their lens. As stated in the Results section (page 263), "the effect of pre-receptoral filtering by the lens is shown in fig 2C. Correcting for lens density shifted the maximum sensitivity of the action spectrum to a shorter wavelength." The extent that this "correction" can influence the spectral sensitivity of user of light therapy can be seen in a later paper by this group (in Exp Gerontology Mar 2005 -Herljevic et al.) where they found that for middle-aged subjects (mean age 57 years) "significantly reduced melatonin suppression was noted... .following exposure to short wavelength (456 nm) light compared to the young subjects." These results likely reflect age-related changes in lens density.

The Brainard study was also concerned with determining the sensitivity of the photoreceptor system and also neutralized the influence on spectral sensitivity from the yellowing of the lens that occurs with age. In this study younger subjects (mean age 24) were chosen, because, as is stated on p. 6406 of the paper "the aging human lens develops pigmentation that attenuates the transmission of shorter visible wavelengths to the retina. In the present study restricting the age of volunteers to 18-30 years controlled for this factor." Brainard determined his peak of 464 nm for spectral sensitivity of the non-vision photic input to the brain by fitting his data to a curve based on theoretical assumptions that have subsequently been found to be incorrect. In fact the data reported in the paper actually demonstrates maximal melatonin suppression at 505 nm and does not demonstrate significantly greater sensitivity at 460 nm than at 505 nm or 480 nm. [Please contact Sunnex Biotechnologies for if you would like a more complete explanation of this]

In contrast to studies by Thapan and Brainard that analysed spectral sensitivity wthout the influence of a normal adult lens, the later studies by Wright and Cooper did not conduct their studies to negate the effect of the adult lens. Wright et al found that melatonin suppression and phase shifts were most sensitive to green light at 480-520 nm, and Cooper et al found that spectral sensitivity was basically flat from 460-500 nm.

In this regard it is worthwhile to note in a study by Benedetti et al. (J Clin Psychiatry, 2003) using 30 minutes of exposure to 400 lux of Sunnex Biotechnologies green light, the "light therapy was individually tailored to produce a 2-hour phase advance to morning light." (Gutman and Goodwin, Neurobiology and Chronobiology of Mood Disorders at the 16th European College of Neuropsychopharmacology Congress, 2003). The 1½ to 2½ hour phase advance of patients in the study obtained with 30 minutes of morning exposure with 400 lux of green light from a Lo-LIGHT lamp compares quite favorably with phase advances induced with 30 minutes morning exposure to 10,000 lux of "bright" light, as reported in the literature.

Extensive trials in the work-place by a U.S. Military Research and Development Center with our Lo-LIGHT lamp have also found that suppression of nocturnal melatonin levels to daytime levels occurs in less than 30 minutes with indirect exposure to 300 lux of green light from Lo-Light lamps and persists for over 2 hours after the termination of exposure. These results were reported from trials conducted on crews of Coast Guard cutters during normal operations and compare favorably with the effect reported in the literature from 10,000 lux of "bright" light. (Aviat Space Environ Med. 2005 Jun;76(6 Suppl):B108-18. Comperatore et al)

It is becoming more apparent that the photic sensitivity and role of melanopsin containing intrinsically photoreceptive retinal ganglion cells (ipRGCs) in hypothalamic stimulation (and visual stimulation- see Barnard et al, Curr Biol Feb 21, 2006) is more complex than was originally thought. For example, papers by Figueiro et al. in Neuroreport 2004, Neuro Endocrinol Lett 2005, and Brain Res Brain Res Rev 2005, on spectral opponency indicate that in addition to melanopsin-containing retinal ganglion cells, rods and cones also appear to have a strong influence on the spectral sensitivity of melatonin suppression in humans, as does light exposure history. Revell and Skene (Chronobiol Intl. Nov 2007) found that "the response to polychromatic light cannot be predicted from the melanopsin photosensory spectral sensitivity and that it is not solely melanopsin that drives the melatonin suppression response"

It is surely incumbent upon therapists to take into account the risks of exposure to blue light wavelengths on the retina. While some do not consider the blue light-AMD link to be proven, there is increasingly compelling evidence that this link exists. In the past two years numerous papers have been published elucidating mechanisms involved in the development of Age-Related Macular Degeneration. See blue light and AMD update Almost all of these papers show results that are consistent with the thesis that blue light exposure induces oxidative stress that contributes to the development of AMD.

There are particular risk factors to ocular health associated with the use of bright or blue light therapy. (See ocular risks from light therapy) Assertions that exposing the retina to increased levels of blue wavelengths from the spectral range of 450 nm to 480 nm will not adversely affect the users vision based on safety standards derived from the intensity of light needed to induce retinal lesions do not address the risk of advancing the users development of AMD from cumulative subthreshold oxidative damage. On the other hand, it has been pointed out that since blue light wavelengths are not necessary for effective light therapy it would be a reasonable caution to filter all blue light wavelengths out of light therapy devices. As one researcher recently stated (Behav Sleep Med 2007; 51(1):57-76. Lack and Wright); "Recent studies have suggested a maximal chronobiotic effect for wavelengths in the range of 420 to 530 nm (deep blue to blue-green; Brainard et al., 2001; Wright & Lack, 2001; Wright et al., 2004). But ironically there is also concern about the so-called 'blue light hazard' with a potentially peak damaging effect in the range 420 to 480 nm ....In the meantime it would be suggested that light in the 500 to 530 nm wavelength range (blue-green) should still be effective while avoiding the putative blue hazard."

Low intensities of green light as provided by Sunnex Biotechnologies lamps are as efficacious as high intensities of white light (400 vs 6,000 lux), and can be adapted comfortably and safely into any environment where light therapy or the regulation of circadian rhythms with light would be beneficial. The latest research supports our position that the use of low intensities of green light as provided by Lo-LIGHT lamps is the optimal source for achieving both efficacy and safety.

If it is helpful to the reader, please note that:
300 lux Sunnex Biotechnologies green light = 19 x 10¹³ photons/cm²
or = (80 microw/cm²)