Present

Newzoo’s authoritative data shows that the number of global smartphone users in 2020 will exceed 3.5 billion. In China alone, the total time spent per capita on various screens is as high as 8.9h per day, of which cell phones account for more than 30%. Young people aged 18-34 in China account for 75.6% of smartphone users.

In recent years, a large number of “cell phone controllers” and “low head people” have appeared, especially among young people. The potential risk of blue light from screen displays on users’ health has received widespread attention. Organic light-emitting diode (organic light-emitting diode, OLED) display panels with self-luminous, thin, low power consumption and other advantages has become the new favorite of the display industry.

Since the beginning of the 21st century, the average annual shipment growth rate of OLED panels is nearly 200%, according to display Bank forecast, OLED will gradually become the mainstream of the display market in the next 20 years. According to different driving methods, OLED technology is divided into automatic matrix organic light-emitting diode panels (AMOLED) and passive matrix organic light-emitting diode panels (PMOLED), and almost all current OLED smartphones are AMOLED.

In 2018, the global AMOLED shipment was 450 million pieces, of which about 400 million pieces were used in smartphones. In the light of the above analysis, it is necessary to study in depth the photobiological safety of blue light in smartphone AMOLEDs for young people.

The light health of smartphone AMOLED mainly includes blue light hazard and rhythm effect. The blue light hazard refers to the damage to the retina of the human eye caused by the photochemical effect of the blue light in the visible light; the rhythmic effect refers to the influence of blue light on the secretion of melatonin, cortisol, etc., which in turn changes the human body’s physiological rhythms and regulates the alertness and biological clock, which is also known as the non-visual biological effect.

Hazard

Noell et al. reported for the first time in 1966 that blue light can cause damage to retinal rod cells, and Dawson et al. confirmed that LED blue light can cause damage to the retina of primates by conducting a blue light hazard test on Indian rhesus monkeys in 2001.

In 2011, Youssef et al. gave a mechanism for blue light damage. 2002, Berson et al. discovered specialized photoreceptor ganglion cells (ipRGC) in the retina. ipRGC connect with the hypothalamic tract of the retina, the suprachiasmatic nucleus of the optic chiasm, the intermediate lateral nucleus of the spinal cord, the ganglion cells in the upper cervical vertebrae, and the pineal gland, and regulate a variety of biorhythms in the human body through the control of melatonin secretion. In 2001, Brainard et al. were the first to determine the non-visual biological spectral response curve, i.e., the rhythm function, which is used to characterize the strength of the influence of different wavelengths of light on human rhythms.

Currently, the blue light hazard and rhythmic effects of artificial light sources have attracted extensive attention from international authorities, for example, CIES 009/E:200, IDT and IEC/TR 62778 have given quantitative analysis methods for blue light hazard (CIE: International Commission on Illumination, IEC: International Electrotechnical Commission). ISO/TC 274N201, CIE TN 003. 2015, etc. have called for vigilance on lighting and rhythmic effects: 2015, etc. all call for vigilance against the rhythmic effects of lighting and displays (ISO/TC274: International Organization for Standardization/Technical Committee on Light and Lighting); three scientists, Jeffrey C Hall, Michael Rosbash, and Michael W Young, were awarded the 2017 Nobel Prize for their discovery of the molecular mechanism controlling circadian rhythms. The 2017 Nobel Prize in Physiology or Medicine was awarded for the discovery of the molecular mechanisms that control circadian rhythms.

Most of the related research focuses on artificial lighting, therefore, the blue light hazard and rhythmic effect of display devices with fast-changing images and high-frequency flickering spectra are the current research hotspots and difficulties.

The blue light hazard and rhythmic effect of various traditional display technologies have been reported, but there is no prospective research on the photobiological health of AMOLED smartphones. Considering the particularity of the age distribution of smartphone users, combined with the authoritative data given by CIE in 2012 on the change of human eye transmittance with age, some scholars have comprehensively investigated the rule of change of blue light hazard and rhythmic effect with the age of users (1-100 years old) in the range of AMOLED color temperature from 2300 to 6500 K. This study is based on the change of blue light harm and rhythmic effect by different color temperatures (1-100 years old).

Conclusion

Based on the spectral distribution of AMOLED smartphone screens with different color temperatures (2300, 2700, 3400, 4100, 5000, and 6500 K) and the transmittance formula for 1-100 years old human eyes given by ciE203-2012A, this study calculates the blue light hazard and rhythmic effect with user’s age (1-100 years old) for six different color temperatures of AMOLEDs respectively. The blue light hazard factor kB and the rhythm factor kc of the effective spectral distribution on the retina of human eyes of different ages are calculated separately to study the changes of blue light hazard and rhythm effect of AMOLED with age, and the following conclusions are obtained:

(1) For AMOLEDs with color temperature in the range of 2300-6500k, the blue light hazard and rhythmic effect on users aged 1-100 years decrease with age, and the rate of decrease increases with the increase of color temperature. Taking 6500k as an example, when the age increases from 1 to 100 years old, the blue light hazard factor and the rhythm factor of the effective spectrum of the retina are reduced to 0.2907 and 0.4038 times of the original ones, respectively.

(2) For AMOLED users aged 1-100, 40 years old is a demarcation point, when the age is older than 40, the blue light hazard factor and rhythm factor of all color temperatures decrease significantly faster with age. 6 different color temperatures, the average rate of decrease of the blue light hazard factor and rhythm factor of the 40-100 years old with age is 1.2907 and 0.4038 times, respectively. At six different color temperatures, the average rate of decrease of blue light hazard factor and rhythm factor with age for 40-100 years old was 2.7482 and 2.9933 times that of 1-40 years old, respectively.

(3) AMOLEDs have a greater blue light hazard and rhythmic effect on young people, especially young users younger than 40 years of age, who should reduce the time of use.