UNDERSTANDING BLUE LIGHT'S EFFECTS

Abstract

DISPLAYS HAVE BECOME AN indispensable part of life—we use computers, tablets, smartphones, and other devices during the day for work, and at night for entertainment. Many of the self-luminous displays use LED backlight technology that includes blue-emitting LEDs with a narrowband emission of 450–470 nanometers (nm). The white backlight is created by combining three colors from red, green, and blue (RGB) LEDs, or by using phosphor-converted white LEDs or blue LEDs with quantum-dot enhancement film. Phosphor-converted LEDs are relatively inexpensive. The technology has been used to create highly efficient white light sources that provide significant energy savings, and LED solid-state lighting is now available in a wide variety of home and industrial products. Phosphor-converted LEDs are also richer in blue components compared to other artificial light sources, and their spectra are significantly different from that of incandescent or fluorescent lamps.1, 2 More to Uncover Some aspects of blue light's effect on health are far from settled. Image: GIPhotoStock/Science Source Presently, blue light's effect on human health—in particular, the human vision system—is highly and frequently debated. It's now well-accepted that the non-visual effects of light significantly impact our circadian system. We need exposure to blue-rich morning light for regulation of our biological rhythms, improved sleep quality, and other health benefits.2 However, overexposure to blue light in the evening, especially from self-luminous displays, results in circadian disruption. But is blue light harmful to our eyes? Displays deliver illumination directly into the eyes, as opposed to the reflected light received when reading paper books. Researchers have found that exposure to bright short-wavelength light (a “phototoxic band” of 440–470 nm) can cause permanent retinal damage; this is often referred to as blue-light hazard (BLH). The light-induced damage can result from viewing either incredibly bright light for a short time (up to 12 hours) or a less bright light for a longer duration (days to weeks). The BLH to the retina depends on the light source's radiance, which does not decrease with distance. To assess the risk, we must consider the source's radiance, its spectral distribution, and the retina's duration of exposure. We obtain the blue-light weighted radiance by multiplying the source's spectrum by the BLH function and integrating the product of this multiplication. The obtained value is compared to the radiance limits. The International Commission on Non-Ionizing Radiation Protection (ICNIRP) provides an exposure limit of 100 watts per square meter per steradian (W m−2 sr−1) for viewing blue light without adverse effects for more than three hours.3 According to the guidelines, if a white light source's radiance doesn't exceed 104 candelas per square meter (cd/m2), evaluating its blue-light weighted radiance isn't required. Displays operate at a lower brightness that doesn't exceed the ICNIRP's luminance value; for example, the maximal brightness of the iPhone X is about 625 cd/m2.4 Still, little is understood about long-term exposure to lower levels. Brightness of LEDs is significantly higher; they offer > 4,000 lumens (Im) per package, which can exceed 104 cd/m2.5 Interestingly, one paper suggested that it would be useful to classify LEDs and other illuminants by their potential hazard to the eye, as they're labeled with respect to their energy efficiency already.6 This issue of Information Display includes the Frontline Technology article “Investigating Blue-Light Exposure from Lighting and Displays,” an important review by two experts in this area of research, John D. Bullough and Stefan Peana. It summarizes current views on blue-light risks and their effect on ocular health. The topic is relevant to you as both a professional in the display industry and a user of displays. It might be prudent, for example, to reduce the color temperature of your display and lower the amount of blue light emitted for viewing comfort and long-term eye health. It was difficult to write this editorial, as there is a lot of information on the BLH topic, as well as some unknowns. But as research continues and our knowledge advances, we will keep you updated. Marina Kondakova, Ph.D., is the director of device formulation at OLEDWorks. She can be reached at mkondakova552@gmail.com.