GreenLIGHT Therapy vs Blue Light Therapy

A technical review of the research

The spectral sensitivity of light therapy for chronobiological disorders

Preface: Harvard University researchers confirmed that the output of Sunnex Biotechnologies' Lo-LIGHT lamp matches the peak sensitivity of the human circadian system. This conclusion followed trials with Lo-LIGHT lamps conducted by researchers in Harvard University's Division of Sleep Medicine for a National Space Biomedical Research Institute project, as well as other studies. As Dr. Czeisler stated: "new information about the peak sensitivity of the human circadian system, determining that the most efficacious specialized light source should have a peak near 500nm (as opposed to ~470nm as the lamps produced by Philips Lighting, Eindhoven, Netherlands, as originally proposed), and therefore identifying such a new specialized light source for our studies; retrofitting our laboratory with specialized lamps (manufactured by Sunnex Biotechnologies, Winnipeg, MB, Canada) with a peak sensitivity near 500nm."

[Quote from NASA's Space Life & Physical Sciences Research & Applications Division Task Book - Evaluation of Photic Countermeasures for Circadian Entrainment of Neurobehavioral Performance and Sleep-Wake Regulation Before and During Spaceflight] See section 'Task Progress'.

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 visible light wavelengths that appear blue or indigo to the human eye, and are made up of visible light wavelengths shorter than 480 nm ( and longer than 400 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 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 visible light 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 range of green light wavelengths that peak near 500 nm.


There is 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 groups 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 and "blue-enriched" light, it is now evident this in not the case. (See Ref- Editorial in Sleep Medicine)

The Surrey University Chronobiology Center demonstrated that blue light (479 nm) is only about as efficient as ordinary white fluorescent light in inducing a physiological response (melatonin suppression), even for young people. Studies at Harvard Medical School and 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. Refs on light therapy and blue light.

In contrast, several research groups have shown Lo-LIGHT lamps using the GreenLIGHT technology are highly effective for regulating human circadian physiology and for treating mood disorders, even though they provide only a small fraction of the intensity needed in studies using “bright” white (polychromatic) light therapy devices. Studies validating the effectiveness of the low intensity GreenLIGHT technology have been published in highly rated journals.

A study conducted for NORAD by the USAF and the Canadian Defence Department on the use of appropriate light exposure for regulating circadian rhythms to improve alertness and performance of night shift workers found Lo-LIGHT lamps were more effective than light therapy devices providing more than 10 times the intensity of light, and were selected for a series of follow-up studies on adaptation to night work and for combatting jet lag.

Lo-LIGHT lamps were also used in the development of light management protocols of the U.S. Coast Guard's Crew Endurance Management System (CEMS), a program designed to reduce night shift fatigue and to improve the performance and health of people working at night. CEMS was the result of several years of trials with Lo-LIGHT lamps, including years of trials on operational Coast Guard cutters and commercial vessels. Links to detailed information on these and other studies can be found on our home page.

Effect of age on the effectiveness of blue light

The human lens yellows with age, acting as a blue light filter which limits the amount of blue light reaching the retina in people over forty. Limiting the amount of blue light that reaches the retina is generally a positive adaptation, as the retina becomes increasingly susceptible to blue light damage with age. However, it also reduces the efficiency of blue light or blue light enhanced therapy lamps for older people. Studies show the age-related reduction of blue light transmission to the retina is associated with a corresponding age-related reduced sensitivity of chronobiological physiology to blue light. (Refs on blue light therapy and aging). 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.

A study from Harvard University published in SCIENCE Translational Medicine, whose authors include a number of researchers whose earlier studies are often cited as justification for the use of increased levels of blue light in light therapy (Brainard, Czeisler, Lockley etc), confirmed that increasing the proportion of blue light wavelengths is of no benefit for light therapy. See more on Harvard study. In contrast, Lo-LIGHT lamps have been found to be as effective as white fluorescent lamps that provide more than 10 times as much light intensity (irradiance). See more about efficiency of Lo-LIGHT lamps.

Spectral sensitivity of the photic pathway to the hypothalamus

The measure of the physiological response to light exposure is determined by the extent of the induced phase shift and by the degree of suppression 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 was also confirmed in an independent study by the Canadian Defence Department's R&D Centre and the U.S. Air Force. See more on the science behind Lo-LIGHT lamps.

This study, comparing the phase shifting capability of phototherapeutic devices, found that with less than 10% of the light intensity(energy), the Lo-LIGHT lamp was twice as effective as a device that emits primarily blue light. 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 [Lo-LIGHT] tower was the best device, producing melatonin suppression and circadian phase change while relatively free of side effects". (Ref on DRDC/USAF study)

The selection of Lo-LIGHT lamps for use in the 105-day Mars Mission by Harvard University attests to the advantages and superiority of the GreenLIGHT technology. In a press release on this project by the National Space Biomedical Research Institute (NSBRI), 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 on Nasa Study

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. 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 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 from Lo-LIGHT lamp. 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 Lo-LIGHT lamps 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 GreenLIGHT 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)

The scientific basis on which blue light and "blue-enhanced" light therapy was justified, i.e. that the spectral sensitivity of the pathway to light sensitive centers in the brain not involved in vision reflects the spectral sensitivity of melanopsin, has been shown to be erroneous. 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". Ref

It is surely incumbent upon therapists to take into account the risks of exposure to blue light wavelengths on the retina. There are particular risk factors to ocular health associated with the use of bright or blue light therapy. (Read more on ocular risks from light therapy). 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 stated (Behav Sleep Med 2007; 51(1):57-76. Lack and Wright); "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."

Since it is now established that blue light wavelengths are of no benefit for light therapy, long term use of light therapy lamps emitting blue light does not appear to be warranted. While the pathogenesis of AMD has proven to be highly complex and is not yet fully understood, there appears to be sufficient information to demonstrate that increased exposure to blue light can significantly increase the likelihood becoming blind. Read - A Logically Sufficient Basis for Establishing that Blue Light Contributes to the Development of AMD. 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 are based on safety standards derived from the intensity of light needed to induce retinal lesions and do not address the risk of advancing the development of AMD from cumulative sub-lethal oxidative damage caused by blue light absorption in retinal cells.

Low intensities of green light as provided by Lo-LIGHT lamps are as efficacious as high intensities of white light (300 vs 10,000 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.

NOTE: 300 lux Sunnex Biotechnologies green light = 19 x 10¹³ photons/cm²
or = (80 microw/cm²)