BLUE LIGHT AND OUR EYES
The eyes are sensitive to a narrow band of light frequencies called the visible light spectrum. Blue light has the shortest wavelength of the visible light spectrum, and blue rays with the shortest wavelengths have the most energy. Blue light is generally defined as visible light ranging from 380 to 500 nanometers (nm). Since the entire visible spectrum ranges from 380nm to 700nm, blue light makes up approximately one-third of all visible light. Our main source of blue light is sunlight, however the number of indoor man-made sources of blue light is on the rise. This includes fluorescent lighting, LED lighting, and display screens such as smart phones, tablets, computers and flat screen TVs. Although they appear white, LEDs have a peak emission in the blue light range (400-490nm range). With changes to the way we light our homes and offices, as well as the increased use of direct illumination for reading, exposure to blue light is increasing.
Exposure to Blue Light
Despite the fact that the eye is good at blocking UV rays from reaching the retina, the eye is not very good at blocking blue light. Virtually all visible blue light passes through the cornea and lens and reaches the retina. The effect of this exposure is cumulative, and the total number of exposure hours is what matters. A child’s crystalline lens is more transparent to short wavelengths – such as blue light – than that of an adult, making children more sensitive to blue light effects than adults.
Exposure to blue light may also contribute to the following:
The human crystalline lens absorbs UV light throughout life and slowly yellows with time. By the age of 20, it has yellowed enough to filter some but not all HEV blue light. However, it is now believed that this absorption throughout life is a contributing factor to aging and cataract formation, and that protection from both blue light and UV exposure can delay the onset of aging of both the lens and the retina.
Too much exposure to blue light can damage light sensitive cells in the retina. This causes changes that resemble those of macular degeneration, which can lead to permanent vision loss. Studies have shown that it is the cumulative effect of this exposure that causes the damage, and that mainly affects the cones (the photo sensitive cells responsible for central vision and colour vision) and the retinal pigment epithelium (cells responsible for nourishing the retinal cells). Lutein, a blue blocking pigment, is found in healthy human retinas and has been shown to protect against the blue light photo damage. Time of day of the exposure may also be an important factor, and research in this area is ongoing.
Computer screens and other digital devices emit significant amounts of blue light and people are spending more and more hours looking at them. The high energy blue light waves scatter more in the eye and is not as easily focused. This scatter creates “visual noise” that reduces contrast and can contribute to digital eye strain.
Certain wavelengths of blue light can help boost mood, alertness, memory, and cognitive function. Blue light is also important in the regulation of the circadian rhythm, the body’s natural sleep/wake cycle. Proper and timely exposure to HEV blue light helps the body to maintain wakefulness, and as the natural blue light (sun) wanes in the evening the restful cycle begins. Therefore, exposure to too much blue light at night through screens and indoor lighting may lead to poor sleep quality, difficulty falling asleep, and daytime fatigue.
Most adolescents prefer sleep/wake cycles that are considerably delayed compared to younger children or adults. As a result, device use in the evening is prevalent in teenagers. This exposure to HEV blue light has been shown to suppress melatonin production, sleepiness, and morning alertness. The eye health industry has responded to this matter by creating filters and apps that filter the blue light from screens at appropriate times, without affecting visibility. Moreover, most lens manufacturers have developed special glare-reducing lenses and coatings to block HEV blue light. An Optometrist can help identify which type of correction may best suit individual needs.
Experimental evidence has suggested exposure to blue light in the 470-490nm range may be less damaging compared to blue light from 400-470nm. Development of LEDs with a peak emission in the safer range may represent an important advancement for ocular health. Blue light exposure in younger people should be monitored and controlled. Over time, accumulated damage from blue light exposure can increase the likelihood and severity of age-related eyes condition such as macular degeneration and cataracts. A healthy diet, high in leafy green vegetables and colourful fruits, may help to increase the levels of the protective pigments in the retina and mitigate some damaging effects of blue light.
Good sleep is essential for attention, learning, mood, and general well-being. The effects of blue light on the sleep cycle may be minimized by:
- Avoiding bright screens for 2-3 hours before bed time
- Seeking some outdoor light exposure in the early hours of the day
- Limiting screen time to no more than two hours per day for children aged 5-18, one hour per day for children aged 2-5 and avoiding it completely for children under 2 years of age.