Light Impacts

Hue and timing determine whether rays are beneficial or detrimental

This is part two of a two-part series on lighting’s environmental and human impacts. Part I: “Illuminating Changes,” is available here.

DROWSY-NOT! The bluish light emitted by computer screens may be sabotaging sleep schedules in teens who work late into the night. The hue might signal the biological clock that it’s morning. iStockphoto
LITE THERAPY. A regimen of light can reset a person’s biological clock when it’s out of sync, but the white, high-intensity glare of the typical light box can cause discomfort. Since the human biological clock is especially sensitive to blue hues, researchers are developing light boxes equipped with blue, low-intensity LED lights, as shown here. Lighting Research Center/Rensselaer Polytechnic Inst.
BLUE BLOCKERS. Yellow-orange glasses, seen here, or similarly colored filters for computer and television screens can block blue emissions that at night may inappropriately reset the body’s internal clock. Hansler/John Carroll Univ.

Erin Chesky was a sleep-troubled teen, typical of many. Despite going to bed early each night, this honor roll student struggled to doze off—sometimes lying awake until 3 a.m. Each morning, she fought equally hard to wake up at 5:30, in time to eat breakfast and catch the school bus. Forever tired, “I was like a zombie,” she recalls.

Last fall, a sleep specialist examined the 17-year-old from Colonie, N.Y. He diagnosed her with delayed sleep-phase syndrome, a condition in which the body’s internal clock fails to synchronize appropriately with Earth’s day-night cycle, which changes a few minutes each day.

From birth, Erin and her siblings were night owls. When Erin turned 15 however, her biological clock really got off-kilter, triggering insomnia that threatened her schoolwork. Her mom recognized the affliction; it had struck her at the same age.

For such teens, adhering to class schedules can be “like swimming upstream,” says psychologist Paul Glovinsky of the Capital Region Sleep and Wake Disorders Center at St. Peter’s Hospital in Albany, N.Y. Some teens fail to make it to school on time, or at all, 30 or more days a year.

Within 4 months, Glovinsky got Erin in sync with her school’s schedule. The high school junior now easily falls asleep by 11 p.m. Glovinsky’s trick: entraining Erin’s biological clock. Each morning, a special lamp delivers a half-hour of intense fluorescent light as she eats breakfast or reads.

Mariana G. Figueiro of Rensselaer Polytechnic Institute’s Lighting Research Center in nearby Troy, N.Y., uses colored light at night to aid elderly institutionalized patients. An early evening treatment from some 50 blue light-emitting diodes (LEDs) coaxes a person’s fractured sleep into solid, nightlong slumber. Elsewhere, researchers are experimenting with color-tuned light to perk up the body, improve visual acuity, and even reduce depression. Such techniques all stem from an emerging realization that for the body, light’s role extends well beyond vision.

Moody blues

Because sunlight is a broad mix of colors, the human eye perceives it as white. Lamps used in past attempts to adjust people’s internal clocks have emitted a broad composite of colors that also appeared white.

However, suspecting that the biological clock preferentially responds to select elements of the spectrum, George C. Brainard and his team at Thomas Jefferson University in Philadelphia launched a 5-year effort to find the most-effective hues. The project tested 72 people and encompassed more than 600 person-nights of observation.

Results, published 5 years ago, showed that the biological clock is most responsive to a narrow band of wavelengths from 466 to 477 nanometers (nm), which are close to the blue of a clear sky.

“It’s not something we would have predicted,” Brainard notes, since these wavelengths aren’t ones to which the eye’s vision receptors—rods and cones—are most sensitive. The receptors called blue cones have a maximum sensitivity of about 430 nm.

Brainard says that an explanation for the biological clock’s blue sensitivity soon emerged in “a landmark paper that stunned the world.”

Four years ago, retinal neuroscientist David M. Berson and his colleagues at Brown University in Providence, R.I., described a new class of light receptors in the human eye. These receptors’ sensitivity peaked at 480 nm. They are located in a minute share of ganglion cells, the information-processing units that send signals to various parts of the brain. Moreover, these cells appeared to be the most important source of information for brain area, the superchiasmatic nucleus, which is “the biological equivalent to the clock chip on your computer,” Berson says.

He says that what prompted his search was a series of animal experiments by others that had shown that blind rodents lacking functional rods and cones still maintain their 24-hour, light-synchronized circadian cycles. Remove eyes, however, and the animals’ clocks drift out of synch with the daily rhythm of light and darkness. Something other than rods and cones must be responsible for the rhythm, Berson and others decided.

To Figueiro, the ganglion-cell discovery confirmed that “our eyes are effectively blue-sky detectors.”

Soon after Berson’s finding, Figueiro and others began testing how well blue light can reset people’s circadian clocks. Over the past 3 years, for instance, Figueiro has worked with eight Alzheimer’s patients who tended to fall asleep around 7 p.m. Their body clocks were running amok—probably, she says, because these shut-ins didn’t encounter blue skies or other light that was bright enough to prevent circadian drift.

Exposure to red light around suppertime for 2 hours each day for 10 successive days had no effect on the patients’ disordered sleep. However, Figueiro found, a similar exposure to blue-LED light prompted the study participants to fall asleep later and then sleep longer and better than they had before the treatment.

Brainard’s team has also investigated blue-light therapy. The researchers tested 24 people with winter depression, also known as seasonal-affective disorder (SAD). Half were given light boxes lit by red LEDs, and the rest had boxes lit by blue LEDs. Early every morning for a month in winter, each volunteer sat directly in front of one of the light boxes for 45 minutes.

In the March 15 Biological Psychiatry, the scientists report that people who got blue-light treatment experienced almost a 60 percent reduction in SAD symptoms compared with a 40 percent reduction in people receiving red light. Moreover, the blue light’s intensity, 400 lux, which is comparable to the light reflected from a well-lit desktop, yielded symptom reductions comparable to those seen in other studies using glaring, 10,000-lux white light.

Mellow yellow

Ganglion cells aren’t the only source of information for the biological clock, says Mark S. Rea, a biophysicist at the Rensselaer lighting center. His team has shown that color-signaling cones can mute the ganglion cells’ impact on the biological clock, as measured by changes in the hormone melatonin.

Secreted by the brain, melatonin not only helps trigger and maintain sleep but also plays a role in regulating the body’s internal clock (SN: 5/13/95, p. 300). Dusk and darkness normally trigger melatonin production, whereas bright light can suppress it.

Rea’s team exposed four men to mercury-vapor lamps in two hour-long sessions at various times between 11 p.m. and 4 a.m. In white-light sessions, the intensity was either 450 or 1,050 lux and always included both blue and yellow wavelengths. In other sessions, filters removed all but 7.5 or 15 lux of blue light. The scientists monitored the volunteers’ blood-melatonin concentrations throughout the evening test periods.

The high-lux, white-light mercury lamp suppressed the nighttime melatonin by 50 percent. So did the 15-lux blue light—despite its low intensity. The low-lux white light didn’t perform nearly as well as those or even the 7.5-lux blue light, which reduced nighttime melatonin by more than 30 percent. The researchers reported their findings in the October 2005 Neuroendocrinology Letters.

The results suggest that yellow light can blunt the body clock’s response to blue light, Figueiro says. When both blue and yellow are present, equal intensities of the two cancel each other. Only if there’s an excess of blue will the cones signal light’s presence to the biological clock.

Yellow-light therapy might be especially helpful in teens, whose body clocks tend to run late. Most people naturally wake about 2 hours after their core body temperature reaches its daily minimum, typically around 5 a.m. However, Figueiro notes, in teens with much-delayed internal clocks, body temperatures may not bottom out until 9 a.m. If intense blue light, such as that present in sunlight, arrives before this time, it may further delay their clock and natural waking time.

Wearing yellow goggles that block out blue hues might enable such teens to reach class on time. They might also want to wear yellow glasses late at night while doing homework at computer screens. Figueiro says that those screens are rich in blue emissions and so suggest the presence of morning when a person’s biological clock should be registering that it’s time to sleep.

Former General Electric Co. lighting scientist Richard Hansler, now at John Carroll University in Cleveland, has teamed with academic colleagues to develop such blue-canceling glasses. In tests, the researchers demonstrated that no blue light passes through the glasses’ lenses.

Glovinsky and others have begun prescribing such yellow glasses to enable sleep-disorder patients to better control when they encounter blue light.

Spectral caffeine?

Bright white light can perk up drowsy people. Steven W. Lockley of Harvard Medical School in Boston and his colleagues decided to test whether specific colors within that light are particularly arousing.

They recruited 16 men and women to spend 9 days in an environment lacking sunlight and its daily time cues. For the first 2 days, the researchers kept the lighting bright for 20 hours a day and totally dark for 4 hours. For the rest of the days, the light was kept dim—less than 2 lux—except for occasional periods of total darkness lasting up to 4 hours a day and, on the sixth day, jolts of intense, colored light.

On that day, the volunteers—by then quite sleepy—encountered 6.5 hours of pure-blue or pure-green bright light during the middle of the night. During that time, tests measured such features as alertness, brain wave patterns, and blood concentrations of hormones.

Compared with people receiving green light, those getting the same intensity of blue light became more alert and less drowsy—4.0 versus 6.5 on a 9-point sleepiness scale. Blue light also triggered brain waves suggesting that the volunteers were more awake.

“[W]e have demonstrated that short-wavelength [blue] light is more effective at stimulating subjective and objective correlates of alertness and performance,” Lockley’s team concluded in the February Sleep.

The researchers argue that if the findings are confirmed, lighting with a strong blue component might improve safety or performance among people who need to maintain sustained vigilance—from long-distance drivers to air-traffic controllers and airport-security inspectors.

Blue hues also heighten visual acuity. Physicist Sam M. Berman of Lawrence Berkeley (Calif.) National Laboratory and his colleagues investigated the phenomenon in 27 fourth and fifth graders in Michigan schools. An optometrist assessed how well each student could read an eye chart under three conditions: bright blue-white fluorescent light, bright reddish-white fluorescent light, and the blue-white light at half its initial intensity.

In the January Lighting Research & Technology, Berman’s group reported that 24 of the students performed significantly better under the higher-intensity bluish light than under the reddish-white light. However, the kids’ performance was indistinguishable between the low-intensity blue-white light and full-strength reddish light. Berman says that schools should consider installing fluorescent lights that emit more blue.

The Department of Energy (DOE) has a related field experiment under way in three California buildings. After surveying individuals’ perception of their office lighting’s quality, crews substituted the commonly used reddish-white fluorescents with lower-lux, bluer-toned ones.

People reported no drop in satisfaction with their office lighting, notes James R. Brodrick, a DOE lighting-research manager in Washington, D.C. Prompting the study, he says, were analyses indicating that “the human retina responds to the slightly bluer light in such a way that the iris closes down a tidbit, improving visual acuity.” This contraction increases the distance over which features remain crisp, comparable to stopping down the lens on a camera.

Furthermore, an unpublished study spearheaded by neuroscientist Paul Gamlin of the University of Alabama at Birmingham demonstrates that the eyes’ blue-sensitive ganglion cells that relay light signals to the biological clock drive this pupil constriction in rhesus monkeys—and presumably people.

Color shifting

Sunlight tends to change over the course of the day from spectra with a strong blue component to illumination dominated by reddish-gold tones. Many of Earth’s inhabitants, including people, have adapted biologically, reading spectral changes as important cues for when it’s time to work or slumber.

With the advent of electric lighting, people created synthetic daylight. However, artificial lighting’s color, intensity, or timing may confuse biological systems. In an attempt to make lighting more natural, comfortable, and healthful, lighting manufacturers have been investigating what they now call dynamic lighting.

For instance, Philips Lighting in Eindhoven, the Netherlands, has developed a computer-controlled system that pairs fluorescent tubes that have different spectral outputs. One tube produces light that’s rich in blue wavelengths, while the other has stronger red and yellow outputs. Nevertheless, both tubes “are basically experienced as white light,” explains Luc Schlangen, a lighting scientist with the company.

In the morning, to perk people up, the lamp increases the blue tube’s contribution to room lighting. As lunchtime nears, controls dim both tubes to save energy but now make output of the second, warmer-toned fluorescent dominant. After lunch, the blue’s contribution again rises briefly to counter afternoon sleepiness, eventually shifting as outdoor daylight wanes, to dimmer, redder lighting. The controls are adaptable, so that customers can personalize the pattern of when and how the spectra vary.

Systems using these lights have already been installed in many facilities throughout Europe, including some hospitals, insurance companies, a town hall, and traffic-control center.

Studies are planned, Schlangen says, to evaluate the extent to which such spectrally adaptive lighting—developed in response to the findings of Berman, Brainard, Figueiro, and others—might contribute to well-being under real-world conditions.

Part I of this series: “Illuminating Changes,” appeared in last week’s issue. Available at Illuminating Changes.

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.