Canadian Occupational Safety

22 Canadian Occupational Safety | www.cos-mag.com W hen the City of Ottawa launched a project to replace its old orange street- lights with 58,000 new LED lamps, it quickly heard some criticism. Experts pointed to research showing a connection between LED (light-emitting diode) lights and health problems. Mixing yellow and blue light creates the intense white of LEDs. "Unfortunately, the blue affects our circadian rhythm," Robert Dick, a physics professor at the University of Ottawa, said in an interview with CBC last year. In the late 1990s, he added, a study found nurses had a 60 per cent higher incidence of breast cancer. After investigating all possible causes, researchers narrowed in on the blue component in light used in the corridors after dark. "It's that blue light that prevents your body from recognizing that it is nighttime. At nighttime, you have a lot of restorative hormones that course through your body that fight disease, infection and that reduce stress and anxiety. They even fight incipi- ent cancer cells," he said. "Those are inhibited when you have blue light shining in your eyes." The amount of blue light we are all exposed to has greatly increased in recent years. The screens on digital devices — smartphones, tablets, laptops and televisions — emit large amounts of blue light. There is also now more blue light in overhead lighting. For many workers, this is a particular problem. Digital devices have become necessary tools in most occupations today. After using them all day, workers go home and continue using them through the eve- ning. The blue light they see at night hinders sleep and can lead to serious insomnia-related problems. Moreover, blue light may cause eye damage over time. But the amount of blue light in the workplace can be reduced, allowing workers to continue using digital devices without the harmful effects. Visible light is emitted across a spectrum of colours. Blue light is light in the blue region, the high-energy end of the spectrum. Measured in wave- lengths, blue wavelengths range from about 400 to 500 nanometres (nm). "Within that range, the shorter wavelengths — about 400 to 450 nm — are the ones that can cause retina damage," says Kirsten North, policy special- ist with the Ottawa-based Canadian Association of Optometrists and a practising optometrist. While we have always been exposed to blue light, mostly from the sun, the amount of blue light we see has greatly increased in the last few decades, North says. Lighting technology has improved in energy- efficiency and longevity, but each new type of light produces more light in the blue spectrum. Fluores- cent tubes and compact fluorescent lamps emit more blue light than the incandescent bulbs they replaced. Fluorescent lighting is popular in overhead fixtures, especially in warehouses. The latest technology, LEDs, emits more blue light than fluorescent lights. LEDs are used in many electronics with screens and are starting to be used more frequently in over- head lighting. BLUE LIGHT AT NIGHT Light, in general, inhibits the production of the "sleep hormone" melatonin, and blue light does this to a greater extent than other types of light. During the day, blue light promotes alertness, but at night, exposure to blue light disrupts the circadian rhythm, the body's 24-hour clock, interfering with a person's normal sleep habits. "The eye detects the light and signals to the brain it's still daytime, and then your brain says, 'Prepare this person as if they were going out during the day.' So, all the physiological things that your body does during the day to keep you awake — raising body temperature, increasing cortisol (a stress hormone), lowering melatonin — it will do at night, when it should be doing the opposite," says Amol Rao, founder of Somnitude in Toronto. Short-term lack of sleep impairs cognitive func- tion. But if persistent, insomnia can eventually contribute to serious physical and mental health problems, such as breast and prostate cancer, diabe- tes, obesity, cardiovascular disease and depression. People working regularly on a night shift are most likely to be affected by blue light. "We know that blue light alters the sleep cycle. So if you're exposed to blue light — fluorescent bulbs, LEDs, screens — during your nighttime and then when you leave it's light outside, you never get that total darkness. There have been studies linking that to all kinds of diseases, including breast cancer," North says. Blue light also creates worse nighttime glare than conventional lighting, one of the reasons for concern about LED street lamps. Blue light produces glare in the eyes and so increases safety risks on the road, North says. "Blue light is harder to focus than other colours. If most of the light coming from LED street lights is blue, then it's harder to focus. It will slow down your reaction time." VISION HAZARDS Over time, blue light may also cause damage to the Increasing exposure to blue light from computer screens, ceiling lights undermining health of workers By Linda Johnson

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