Guest post by VSP optometrist Gary Morgan
There is no escaping the fact that most of us are surrounded by digital devices. Whether in the office, at home, or in the palm of your hand, these devices are ubiquitous. They also emit harmful blue light and there has been a lot of media interest about the impact it is having on our health. As part of that conversation, an unsettling term has surfaced: good blue light. How did this term come about? First, we need to take a step back and discuss blue light in terms of wavelength. Our visual system detects wavelengths of light between approximately 400-750 nanometers (nm). The shorter wavelengths have higher energy and a cooler color (blue light is defined as 400-500nm). We can also further divide these wavelengths of light by their effects on our vision and health.
What is “bad” blue light?
Blue light below 430nm is most responsible for the tired feeling our eyes may get after viewing digital screens; we call this digital eyestrain or visual strain. Blue light below 460 nm is what has been linked to oxidative retinal damage. The cumulative effect of this light has been linked to the potential development of age-related macular degeneration (AMD), the leading cause of blindness for people over 55. So light below 460nm has been labeled ‘bad blue light’
What is “good” blue light?
Blue light above 460nm controls the secretion of our sleep hormone, melatonin. In what used to be considered a normal day, we would wake up in the morning, receive exposure to sunlight, and our body’s internal clock would tell our pineal gland to stop secreting melatonin. This would make us feel awake, alert, energetic, and some would say happy. This is how we want to feel during the day, thus the term ‘good blue light’ has been used to describe these longer blue wavelengths. In fact, in some climates where sunlight is scarce during winter, people have less blue light exposure and may develop seasonal affective disorder (SAD) in which they feel tired and depressed. Therapy lights that emit long blue light wavelengths are a common treatment for SAD.
When does “good” blue light go bad?
Digital devices emit the full spectrum of blue light. Exposure to longer wavelength blue light at night affects melatonin secretion and disrupts our sleep. Should we really classify 460-500nm light as good when it interferes with our ability to fall asleep? Is it a good thing that our children are not getting enough sleep, which for some may lead to ADHD-like symptoms? How happy are we to be awake at 2:00 a.m. because we worked on our computer or tablet until 11:00 p.m., delaying the onset of melatonin secretion?
None of these implications that are currently being extensively researched sound very good. While we need exposure to 460-490nm light during the day, we don’t need it after sunset. So when you hear the term ‘good blue light’, take care to keep it in the proper context. Your health could depend on it.
Learn more about how you can reduce blue light exposure with lens coatings like Sharper Image TechShield.