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A few years ago I was having trouble sleeping. My wife, who at the time was editing a breast-cancer blog, told me about the connection between blue light and the body's 24-hour circadian rhythm, which dictates all sorts of things ranging from when you get sleepy to what your levels of stress hormones are. It turns out that in addition to the rod and cone cells in the eye used for vision, there are special retina cells that send timekeeping signals to the entire body, based simply on the presence or absence of blue light. During most of mankind's existence, blue light happened only in the daytime, so the signals from the timekeeping cells were a reliable guide to what time it was. But since the advent of artificial light, especially artificial blue light, these signals have become scrambled.
Studies have found that women with nighttime jobs or other circumstances that expose them to blue light for longer than the normal daylight hours run an increased risk of breast cancer, and also suffer sleep problems. So I bought some orange sunglasses that were guaranteed to block nearly all blue light and wore them in the evenings.
I wish I could say my life was changed for the better, but frankly, I didn't notice any major immediate difference in my sleep patterns, so I quit wearing them. Eventually I got to where I was sleeping better anyway, and I forgot about the whole thing until I read recently about a meta-study of light exposure and human health by Richard Stevens, a cancer specialist at the University of Connecticut.
As reported in Wired's online edition, Stevens cites evidence connecting nighttime light exposure with obesity, breast cancer, and depression. But the problem with these results is the same as the question of whether wearing those sunglasses really helped my sleep patterns or not: what other factors are at play here?
I come from a physics and electrical engineering background where truly controlled experiments are easy to do. One of the introductory labs we put our sophomores through is to wire up a circuit with resistors and a power supply, and verify that it obey's Ohm's Law. With decent equipment and careful measurements, anyone can get experimental results in a few minutes that are within 1% or so of the theoretical predictions.
Hardly any experiments involving human beings work out that accurately, except perhaps for actuarial studies that predict simple things like death rates per million people in well-understood populations. But an individual human being is such a complicated system with so many unknowns in its history that predictions about anything concerning an individual's health are often little more than educated guesses.
When a factor as ubiquitous as artificial light containing blue wavelengths is involved, the problem gets even harder. Without putting experimental subjects in a totally controlled environment for long periods of time—a prohibitively expensive undertaking—researchers are forced to simply ask questions about work schedules and environments. These questions cannot possibly capture all the variables at play, and so you are left with the uneasy feeling that if a significant effect can be found despite the crudity of the data available, there may be something even more remarkable out there, if only the experiments could be performed to find it.
Should computer display and illumination engineers worry about this issue? After all, they are the ones who have brought us all this nighttime blue light, first with mercury-vapor lamps, then with fluorescent lighting, then the blue LED and its progeny. High-intensity LED lighting is rapidly replacing older forms of illumination, and its spectral content is relatively high in the blue region. The old incandescent lamps produced relatively little blue light, but no one really knows how much is too much or whether any at all is harmful, so there is no point speculating about whether we have made a bad bargain by trading in our old incandescent bulbs for LED units.
You can take various approaches to this issue. One is the "if it was really bad, we'd know about it already" approach. If seeing blue light at night was as bad for you as licking paintbrushes full of radium paint, we would have seen a major die-off in the printing trades around 1905, when the Cooper-Hewitt mercury-vapor lamp showed up in newspaper printing plants across the country where the morning editions were being printed for the next day. But no such die-off occurred.
On the other hand, in the 1920s, radium was being used in fluorescent paint to make clock dials glow at night, and the women who painted the dials often licked the brushes to point them. Soon, many of these workers began to suffer bone fractures and deterioration of the jawbone, and these health problems were traced to the radium that had concentrated in their bone tissue. Despite initial denials of responsibility by their employer, the so-called "Radium Girls" eventually won in court and established an important precedent in the field of workplace safety.
Whatever the health risks of seeing blue light at night are, it can't be as bad as that. Nevertheless, there are some troubling increases in various diseases that epidemiologists currently have no explanation for, and one wonders whether blue-light exposure may be a factor.
The opposite approach would, I suppose, be to buy yourself a pair of orange sunglasses and put them on at sundown every day. That might help you, but it wouldn't do anything for the millions of people around the world who are staying up till 2 A. M. tweeting or Facebooking or playing online games. And that brings up another issue: how to disentangle the effects of sleep-cycle disruption from exposure to light at night. People generally have to be awake to see any kind of light at night, so when you have one, you have the other. And there is an equally large body of data showing that inadequate or disrupted sleep causes health problems too.
Perhaps some day a researcher will get to the bottom of this question, either with a massively funded study or through some other insight into the problem. In the meantime, all I can say is to go easy on too much TV-watching or Internet-surfing at night, and try to get a good night's sleep. Even if you're an illumination engineer.
