If you haven’t started hearing about the “benefits” of blue light therapy yet, you will soon. Blue light boosters argue that it may be more effective than white light, and that it is the therapeutic ingredient of standard white light that eases seasonal depression.
In order to understand this debate, you will have to refresh your memory about the physics of light.
The bright white light that you see when you gaze into a standard fluorescent light therapy lamp includes essentially all wavelengths of visible light that our eyes can see. However, these lamps are designed to emit most of their light close to a wavelength of 550 nanometers (nm). Why? Because vision scientists have determined that this is the wavelength to which our eyes are most sensitive. However, recent studies indicate that this may not be the ideal wavelength for affecting our circadian rhythms, and by extension, our moods.
Recall from high school physics that light is a form of electromagnetic radiation (EMR), and that all things in the universe either emit, absorb, or reflect EMR. EMR comes in a very wide spectrum, ranging from gamma rays (very short wavelengths and high frequencies) to radio waves (very long wavelengths and low frequencies). Somewhere in the middle are those wavelengths that we can see – the “visible spectrum,” ranging from about 400 to 700 nm.
In order to comprehend the literature on light therapy, it’s helpful to recall an ancient mnemonic (Isaac Newton first devised it) for the wavelengths of specific colors of visible light: ROY G BIV. The letters stand for colors (Red, Orange, Yellow, Green, Blue, Indigo, Violet), and the wavelengths decrease as you go from red (700 nm) to violet (400 nm). The dreaded ultraviolet (UV) radiation is shorter than 400 nm, and causes sunburn and eye damage with excessive exposure.
Our eyes use rods and cones to distinguish different colors of light, and it has always been assumed that the therapeutic action of bright light is caused by activating these vision cells, which then send electrical messages to various parts of our brains. But in 2001 researchers discovered an entirely new mechanism of light perception – essentially, a new way of seeing (J Neurosci 2001;21(16):6405-6412). As it turns out, in addition to rods and cones, our eyes contain special ganglion cells coated with a chemical called melanopsin. Like rods and cones, melanopsin is activated by light, but it is choosy, responding preferentially to light in the wavelength range of 446 to 477 nm – that is, blue light. Melanopsin sends signals to the suprachiasmatic nucleus in the hypothalamus, which ultimately leads to decreases in melatonin levels. Decreasing melatonin, in turn, signals the circadian system to make a shift toward daytime.
Armed with this intriguing finding, light therapy researchers wondered if, since blue light is responsible for changes in melatonin and since light therapy effectiveness is often correlated with melatonin changes, perhaps blue light therapy would be especially effective for seasonal affective disorder (SAD).
Thus far, only two studies have been published testing this theory, one with positive and one with negative results. The first study was published in 1990 and used a crossover design, in which 18 patients were randomly assigned to two out of three possible conditions: white light, blue light, and red light. White light was more effective for depressive symptoms than either blue or red (J Affect Disord 1990;20(4):209-216), a result that refutes the value of blue light. The second, more recent study, used a more rigorous methodology in that 26 patients with SAD were randomly assigned to either blue light treatment (wavelength of 468 nm) or dim-red light treatment, which was used as a placebo control (wavelength 654 nm). In order to test the adequacy of the placebo, all subjects completed an “expectation” scale; there were no differences in positive expectancy between the two treatments (Biol Psychiatry 2006;59(6):502-507).
Patients brought the light panels home and were instructed to sit in front of them for 45 minutes between 6 AM and 8 AM every morning for three weeks. At the end of each week, patients were rated blindly with the Hamilton Depression Rating Scale – SAD Version (SIGH-SAD). The results? Blue light treatment was significantly more effective than red light, with statistically greater reductions in the SIGH-SAD. The blue light remission rate was 55%, compared with the red light rate of 31%, but this difference was not statistically significant, presumably because the sample was too small to detect such a difference.
As you can see, research on the efficacy of blue light is in its infancy, although this hasn’t prevented manufacturers of the technology from making fairly exorbitant claims in its support. For example, Apollo Light Systems, a leading maker of blue lights, proclaims on its website that its new blue wave technology is “clinically tested and published as an effective antidepressant treatment for Seasonal Affective Disorder” (www.apollolight.com). While the evidence base is clearly too weak and preliminary to support such a claim, the FDA, which regulates these matters, has thus far taken a hands-off attitude.
The evidence for blue light’s efficacy needs to be particularly strong for most clinicians to recommend it. Why? Because some concerns have been raised about blue light’s safety. Recall that blue light’s wavelength, around 460 nm, is not too far from the wavelength of UV radiation (<400 nm). Some authorities are concerned that even well-calibrated blue spectrum light might increase the risk of macular degeneration. The researchers who tested blue light therapy in the Biological Psychiatry article reported that their device (which was manufactured by Apollo Lighting Systems) was well within international guidelines for photobiological safety, but they also acknowledged that we have no information about the hazards of long-term exposure to blue light, or to high intensity white light for that matter.
It’s clear that the jury is still out on blue light’s efficacy and long-term safety, but hopefully you are now better informed about the background issues involved.
TCR VERDICT: Blue light: The jury is definitely out!