1University of Chinese Academy of Sciences, 19 A Yuquan Rd, Shijingshan District, Beijing, 100049, China
2Human Ergonomics and Health Display Laboratory, Global R&D Center, TCL Electronics Holdings Limited, Shenzhen, 518000, China
Correspondence
Honglei Ji, University of Chinese Academy of Sciences, Beijing 100049, China.
Email: jihl@tcl.com
Funding information
National Key R&D Program of China,
Grant/Award Number: 2017YFB0404600
Abstract
The ever-increasing utilization of blue light-emitting diode in the field of the display has brought great damage to human eyes. Here, we demonstrate a method that reduces the damage caused by high concentrations of short-wavelength blue light. Our wide spectrum and low peak backlight technology are based on replacing the existing common blue chip with a combination of shortwave blue chip and long-wave blue chip. At the same time, a large number of blue-filtering dye particles are coated on the optical film to reduce high-energy blue light and achieve the effect of protecting the eyes. Therefore, our project can achieve up to 25 nm FWHM and a 50% reduction in peak blue light that is close to the continuous spectrum of natural light in the blue wavelength
region. Numerical and experimental results, in a good agreement, demonstrate good performance of the proposed approach in liquid crystal display, with potential applications to eye-friendly display.
KEYWORDS
eye-friendly, liquid crystal display, low peak energy, wide Spectrum
Display technology has gradually but deeply changed the lifestyle of modern people, especially the liquid crystal display technology.1 According to a recent survey,modern people spend an average of 6 h and 50 min a day looking at screens at least in the 30 countries surveyed.2
The people who spent the most time on screens were Indonesians, who spent 9 h a day. The shortest was the Italians at 5 h and 17 min. At present, most of the backlights of LCD TVs use white light, which is transformed from high-energy short-wave blue light, emitted by the blue chips through phosphors or quantum dots.3–7 The dominant wavelength of a traditional blue chip is about 450 nm. According to our experience, the color gamut and luminous efficacy would decrease when the dominant wavelength moves over 460 nm.8,9 On the other hand, the backlight will have high total energy and strong peak energy when the dominant wavelength of the blue chip moves below 450 nm.10 In this case, short-wave blue light can cause oxidative stress and cytotoxins in cells, reduce the secretion of melatonin, and cause insomnia and visual fatigue.11–13 More seriously, the blue light can directly enter the retina through the lens to cause epithelial cell death, leading to macular disease, cataracts, and glaucoma.14–17
The traditional eye-friendly technology adjusts the ratio of red light, green light, and blue light in the display device through a software algorithm. In this way, only some of the total energy of the blue light is filtered out, leaving the dominant wavelength and FWHM unchanged. 18,19 Meanwhile, in order to keep the white picture from undergoing huge changes, the algorithm will also reduce the brightness of green light and red light, which will further cause the overall brightness of the screen to drop and color shift.20
For reducing the damage of short-wave blue light and peak blue light and brightness attenuation, we propose improving the backlight source and backlight architec ture by our technology. This paper is based on two bases: a dual-component blue chip and a dye that absorbs peak blue light. The specific solution is as follows: We use a dual-combination blue chip that consisted of two different chips with dominant wavelengths of 450 and 460 nm. As a result, the peak of blue light shifts from 430 to 450 nm to the right side of 455 nm, which reduces the intensity of blue light in the range of 415–455 nm. Furthermore, the luminance and gamut remained of television unchanged, and the half-wave width is increased from 19 to 25 nm. In addition, we use dye technology to filter unwanted blue light. Therefore, the spectrum of the display screen is as close as possible to the continuous spectrum of natural light that is beneficial to human health but does not change the picture quality visibly.
2 | THE IMPLEMENTATION AND MANUFACTURING METHOD OF THE WIDE SPECTRUM AND LOW PEAK BLUE LIGHT BACKLIGHT
It is well known that the structure of LED includes bracket, chip, packaging glue, and gold wire.21,22 Figure 1 shows the schematic diagram of LED. The LED bracket is preferably made of Poly1,4-cyclohexylene dimethylene terephthalate (polyphthalamide, epoxy molding compound, and other materials can also be selected), which has multiple functions of conducting, dissipating heat, and supporting and protecting the chip. The dual combination blue chip consists of 450 nm blue chip and 460 nm blue chip, which provide a light source for the TV. The packaging glue that plays an important role in cutting off from the air is made of epoxy, silicone, or polyurethane, etc. Because of the excellent performance of silica gel in heat resistance, UV resistance, water vapor
resistance, thermal shock resistance, expansion coefficient, etc., we choose it as packaging glue. Phosphors are usually added to the packaging glue if quantum dot technology is not used. The gold wire has good conductivity, ductility, and weldability.
We built a direct backlight module based on the dual combination blue chip, as shown in Figure 2. The reflecting plate that can above the back panel but under the light bar. The optical films are usually composed of diffuser plates and various brightness-increasing films. If the LED does not contain phosphors, a quantum dot film needs to be added above the diffuser to convert blue light into white light. The QD film encapsulates the red and green light-emitting quantum dots between two protective films and generates a high-purity light source through photoluminescence to achieve high-color gamut picture quality. We combine blue light-absorbing dyes and PET optical substrates into a blue light filter film. The blue light filter film can reduce the transmittance of blue light and achieve the effect of filtering out some harmful blue light. In order not to affect the photoelectric efficiency of the backlight, we place the blue light filter film under the brightness enhancement film. At the same time, the blue light filter film also has strict requirements on the blue light absorption rate. Absorbance in this article specifically refers to the ratio of the absorbed blue energy to the total backlight blue energy in the wavelength range of 440–460 nm. If the absorption rate is too low, the effect is not obvious, but if the absorption rate is too high, it will filter out the harmless blue light and cause color distortion. The blue light filter film used in this article has an absorptivity in the range of 20–24%.
3 | EXPERIMENTS UNDER DIFFERENT BACKLIGHT SCHEMES
We conducted comparative experiments based on common QD TVs, KSF phosphor TVs, and YAG phosphor
TVs for verifying the eye-friendly effect of our technology. The experiment is divided into three parts: (1) the performance of eye-friendly technology in quantum dot TVs, (2) the performance of eye protection technology in KSF phosphor TVs, and (3) the performance of eye pro tection technology in YAG phosphor TVs.
We evaluated the TV in the experiment in terms of brightness, peak wavelength, the proportion of shortwave blue light, peak ratio, and FWHM. Here, use T to represent the proportion of shortwave blue light. The proportion of short-wave blue light is defined as the ratio of the brightness of the short-wave blue light from 415 to 455 nm to the total brightness of the blue light band from 400 to 500 nm in the range of 400–500 nm. The peak ratio is denoted by U, which is defined as the ratio of the peak value of blue light to the peak value of green light. The color gamut standard adopts the international TV standard DCIP3 color gamut.
3.1 The performance of eye-friendly technology in quantum dot TVs
In this part, we have prepared three QD TVs with the dominant wavelength of 450 nm, one of which does not make any changes, one replaces the 450 nm blue chip with dual-combination blue chip, and the last one uses both a dual-combination blue-chip LEDs and blue light filter film. The test results are shown in Table 1 and Figure 3.
It can be seen from Table 1 and Figure 3 that the dual-combination blue-chip can shift the blue peak energy wavelength from 446 to 456 nm and increase the half-wave width from 19 to 28 nm, effectively reducing the blue light intensity in the range of 400–450 nm. Meanwhile, the brightness reduction is less than 1%, and the color gamut does not change much. After the combined use of dual combination LED and blue light filter film, the proportion of short-wave blue light is further reduced to 44%, and the peak ratio was further reduced to 0.49. Obviously, the half-wave width is further widened to 30 nm. In the actual viewing experience, the blue of the C1-TV is more like sky blue, which looks more comfortable, not as glaring as A1 TV.
Human eyes have evolved to prefer natural light and color. Based on this, it can be considered that the solar spectrum does little harm to human eyes. Since the light we see is usually reflected light, we compare the spectrum of the C1-TV with the reflected sunlight from the ground (in the blue area), as shown in Figure 4. It can be seen from the figure that the C1-TV is much closer to the
sunlight spectrum.
3.2 | The performance of eye-friendly technology in KSF phosphor TVs
In this part, we have prepared three KSF phosphor TVs with the dominant wavelength of 450 nm, one of which does not make any changes, one replaces the 450 nm blue chip with a dual-combination blue-chip, and the last one uses both dual-combination blue chip LEDs and blue light filter film. The test results are shown in Table 2 and Figure 5.
FIGURE 3 The spectrum of different QD TVs
FIGURE 4 Spectral comparison of blue region of different light sources
FIGURE 5 The spectrum of different
3.3 The performance of eye-friendly technology in YAG phosphor TVs
In this part, we have prepared three YAG phosphor TVs with the dominant wavelength of 450 nm, one of which does not make any changes, one replaces the 450 nm blue chip with a dual-combination blue-chip, and the last one uses both dual-combination blue chip LEDs and blue light filter film. The test results are shown in Table 3 and Figure 6.
From the data in Sections 3.2 and 3.3, it can be seen that the dual-combination LED and blue light filter film technology proposed in this article is not only applicable to quantum dot TVs, but also phosphor-type TVs, but the effect is not so significant. In summary, our technology is best used with quantum dot technology to achieve eye protection and high image quality.
FIGURE 6 The spectrum of different YAG TVs
FIGURE 7 The blue image of different TVs (A) our eye-friendly TV (B) ordinary TV
4 | OPPORTUNITIES AND CHALLENGES
By using the dual-combination LED and blue light filter film, the pure blue image turns to azure, as shown in Figure 7. Our eye-friendly technology, which is close to sunlight, leads to intuitive visual experience for consumers in a short time. As a result, our eye-friendly TVs look more comfortable than ordinary TVs.
Low blue light eye-friendly technology has attracted more and more attention in the electronic display industry because of its simple process. It is spreading from high-end TV products to low-end products, we judge that technology will grow explosively in these few years. The technology in this paper is expected to be applied in terminal products in 2022. As a new technical form, low blue light technology still faces some challenges.
At present, there is no unified low blue light standard specification. By the way, although the warm color temperature is better for the human eye, people have different degrees of preference for color temperature. Cool color temperature increases alertness and arousal, while the warm color temperature is more comfortable to watch for a long time.
5 | SUMMARY
Based on the theory of high-energy shortwave blue light and peak blue light damage to the eyes, this paper proposes a method to reduce the damage to human eyes by reducing the proportion of shortwave blue light. Here, we show that by judicious design of dual combination LED and blue light filter film, it is possible to change the short-wavelength blue light into a wide spectrum and low peak energy blue light, thereby achieving eye protection. By using our eye protection technology, the peak energy wavelength of blue light can be shifted to the long-wavelength band, and the half-wave width is increased from 19 nm to more than 25 nm, and the peak ratio is reduced by 50%, making the spectrum of the display close to the natural continuous spectrum. What’s more, the picture quality will not turn yellow or dark and the original color temperature of the display can be maintained. This phenomenon demonstrates that our technology can provide the best viewing effect while protecting consumers’ eye health. Through the research in this article, the technology can be applied to the fields of television and electronic device display screens.
ACKNOWLEDGMENT
The authors would like to gratefully acknowledge the support of the National Key R&D Program of China (2017YFB0404600: Development and application demonstration of key technology of quantum dot backlight).
ORCID
Honglei Ji https://orcid.org/0000-0001-5645-6857
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AUTHOR BIOGRAPHY
Dr. Ji Honglei graduated from Harbin Institute of Technology in 2002, received Master’s degree in Material Physics and Chemistry from Changchun University of Technology in 2007, and his PhD in Material Research from Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences in 2017.
In 2007, he began to research and develop LED backlight technology. In 2010, he joined TCL Multimedia Co., Ltd. and began to devote himself to the development and application of PL quantum dot backlight products in 2012. In 2015, he won the Guangdong Science and Technology Progress Award. Several articles and patents related to PL quantum dot diaphragms have been published. He is a member of Technical Committee of SID Beijing Chapter in 2017, the expert of IEC TC110 group, and the technical member of China National Nano Standards Committee. He is the head of State Key Science and Technology Projects.
How to cite this article: Ji H, Li P, Fu W, Li Z, Ge Z. The application of wide spectrum low peak blue light technology in health TV display. J Soc Inf Display. 2022;30(7):567–573. https://doi.org/10.1002/jsid.1110
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