1 Demand for healthy lighting
After the development of semiconductor material technology and the improvement of manufacturing technology in the past decade, white light emitting diode (LED) as a new type of solid-state light emitting device has gradually replaced the traditional light source. Its high light efficiency, low energy consumption, pollution-free, long life and other advantages make its penetration in the lamp market increased year after year. However, with the rapid development of LED light source, various lighting applications put forward new requirements for light source. From the initial emphasis on the efficiency and cost of LED light, people gradually develop to the pursuit of its light quality and health. At present, some light sources in the market are lack of spectrum and poor color restoration. Some LED lights have many problems, such as stroboscopic, glare, eye safety and so on, due to improper use of driving power, which make the user experience poor. Therefore, in order to meet consumers'demand for quality of life and comfort, high-light quality, comfortable and healthy lighting technology has become the mainstream trend of recent market development, and also poses new challenges to white LED packaging and module technology.——LED Bulb Light
2. Technical scheme of full spectrum white light
At present, there are two main ways to achieve white light: the first is to achieve white light through multi-color LED multi-chip combination (no phosphor). The main technical route is to solve the "yellow gap" problem, and yellow LED chips become the main technical bottleneck. The research team represented by Professor Jiang Fengyi of Nanchang University is devoted to the development of high-efficiency yellow-light LED chips on silicon substrates, and has made key progress. The electro-optic conversion efficiency of yellow-light LED has exceeded 22.7%, reaching the leading position in the industry (Figure 1). Because of the high requirement and the high initial cost of the white light technology, and considering the color instability caused by the difference of light and color which may occur during the long-term thermal operation of the multicolor chips, the application field is still limited although it has great potential.——LED Bulb Light
The second method is to stimulate a variety of fluorescent materials to achieve continuous white light spectrum by monochrome LED chips. Due to the simplicity of chip material and structure, low cost of packaging and control, it is the main scheme to realize full spectrum white light. Fluorescent materials coated on blue or other monochrome LED chips are converted to white light, so fluorescent materials are the key factors to determine the quality of white light and color reduction effect. In the past, the conventional combination mode of blue chips + yellow or green / red phosphors in the market will lead to excess blue light of white LED, shortwave blue light (~490nm) missing and shortage of long-wave red light. The new full spectrum LED has been greatly improved and optimized in the selection and proportion of chip and phosphor, so as to achieve a high quality white lighting experience similar to natural light.——LED Bulb Light
High quality white LED lighting embodies in four aspects: comfort, authenticity, safety and health. It has excellent visual comfort (appropriate brightness and brightness uniformity, no flicker and glare), high color rendering, eye safety and catering to the regulation of circadian rhythm, etc., to meet the psychological and physiological health of consumers. From the perspective of LED packaging, high-quality white LED light source should have a high color rendering to present the true color of the object, that is, the light source spectrum is closer to the standard light source of sunlight or incandescent lamp, with good continuity and smoothness. Secondly, the light source does not contain ultraviolet (UV) and infrared (IR) radiation, and conforms to the human eye sensitive curve. At the same time, it satisfies the high requirements of light quality and color saturation resolution. For example: high fidelity and color saturation lighting meets the needs of museums and galleries; commercial lighting can provide shopping environment with less color difference, which is conducive to the sale of commodities; surgical lamp lighting can correctly display the color of blood, skin and wound tissue; educational lighting can restore the strong picture of books and improve learning attention; video camera live transmission, good color Color saturation and high fidelity make the atmosphere more clear and real; for home lighting, high quality white light makes people feel more comfortable and enjoy life more. In order to more accurately measure the ability of light source to restore object color, the industry began to adopt new methods to evaluate and compare the performance of color quality of different light sources. For example, on the basis of CRI test, IES TM-30-15 evaluation standard was added to evaluate the two-parameter system of color fidelity (RF) and color gamut (RG), aiming to solve the problem of insufficient representation of contrast color and asymmetry of color space in CRI system. Problems such as discontinuity of reference light source. In addition, low proportion of high-energy blue light is considered to reduce the potential harm of blue light in spectral design, and the color temperature and brightness of LED are regulated by packaging design and sensing to meet the needs of sunshine and use scenarios, and in line with human physiological rhythm.——LED Bulb Light
3. Blu-ray hazards and characteristics of health light sources
Although experts from academia, industry and medicine have reached a basic consensus that it is safe for human eyes to use qualified white LED lighting products correctly, the maximum absorption wavelength (440-450 nm) of conical cells induced by blue light in human eyes coincides with the emission wavelength of commonly used blue light chips and the characteristic curve of blue light damage in retina. Therefore, people will be particularly concerned. The effect of high energy blue light on the eyes of sensitive people. As shown in Fig. 2, the blue light damage curve refers to the band located at 415-455 nm (peak: 435-440 nm). Because of its short wavelength and high energy, it can penetrate the lens to the retina. The blue light component in the light power may cause potential chemical damage to the retina, accelerate the oxidation of macular cells, and cause visual fatigue and retinal diseases, such as senile macular degeneration (AMD). Some relevant safety standards and reference documents have been introduced at home and abroad as support. IEC/EN 62471:2006 has established a methodology for assessing the Photobiological Safety of lamps. ANSI/IESNA RP-27 of North America establishes standards for photobiosafety of lamps and luminaire systems. IEC/TR 62778 specifies the categories of general lighting service lamps and lanterns, and provides guidance for the application of blue-light hazard classification to LED lighting products. The standard EN 60598-1:2015 for general safety requirements of lamps and lanterns is updated to meet the requirements of LED lamps and lanterns, which mainly includes: for blue light damage of LED light source, a clear hazard level requirement (RG0/RG1/RG2/RG3) is added; and based on different hazard levels, there are corresponding labels, instructions and installation requirements of fixed lamps and lanterns. In addition, considering that the blue light transmittance and sensitivity of the eye structure of children and the elderly are relatively weak compared with adults, there are some evaluation methods for their tolerance to blue light hazards, but there is no uniform standard. In addition, the degree of high-energy blue light hazard is related to the dose. The greater the intensity of blue light, the higher the hazard level.——LED Bulb Light
The following three parameters are multiplied to obtain the dose of blue light:
1. The proportion of blue light in the spectrum of the light source itself; 2. the brightness of the light source itself; 3. the time of being illuminated by blue light.
And these three points are also the three directions that lamp designers often adopt to prevent from being harmed by blue light.
1. Choose a light source with low color temperature; 2. Reduce the brightness of the light source, such as increasing the diffuser plate to avoid direct light source to eyes; 3. Do not work too long in a very strong light environment. In addition, we can consider to minimize the proportion of high-energy blue light from the light source design.
However, blue light is also a basic component of white light. The visual process of blue light in spectra ranging from 400 to 500 nm includes the important wavelength of color perception. Studies have shown that 465-495 nm blue light plays a crucial role in the circadian rhythm (Fig. 2). Because this part of light can inhibit the production of melatonin, adding this part in the daytime spectrum can ensure the efficiency of operation, keep people awake and alert, and promote work enthusiasm and focus. At night, the functions of promoting sleep and adjusting jet lag can be achieved by reducing blue light or color temperature. Therefore, according to the different time and life needs of the day, combined with the requirements of visual comfort, eye safety and circadian rhythm, through the design of light source, COB package with continuously adjustable color temperature, combined with sensors and controllers, the continuous adjustability of color temperature and brightness can be realized to meet the requirements of various scenes and high-performance lighting matching with sunshine time (fig. 3). Through the effective regulation and control of LED spectrum, LED has gradually surpassed traditional lighting in light quality and artistic effect. Even in the field of hotel and retail lighting, which is considered to have comparative advantages in traditional lighting, LED light source can provide more full color restoration effect.——LED Bulb Light
4 Relevant Enterprises and Representative Products
SORRA Company of the United States took the lead in introducing the full spectrum light source products, using GaN substrate growth to produce purple LED chips, exciting red, green and blue phosphors to convert purple light into white light, including 400-700 nm visible spectrum, CRI95 and R9 are more than 90, which have a bright white effect on brightener objects containing 400-480 nm excitation. Recently, Toyota Synthetic and Seoul Semiconductor Co. Ltd. in Japan have introduced a series of full-spectrum white light sources through similar purple or low-wavelength blue-light excitation phosphor conversion. For example, driven by 200 mA, the light efficiency of 5000K color temperature LED reaches 110 lm/W, realizing a spectrum close to natural light (fig. 4), accurately presenting the color and structure of objects in natural light. The realization of white light has recently attracted the attention of commercial lighting.——LED Bulb Light
In addition, another technical route to achieve high-quality white light in the market is to simulate the continuous spectrum of sunlight while minimizing the harmful UV and high-energy blue light spectrum to human eyes. While achieving high color rendering index, the lumen efficiency is not significantly sacrificed; while ensuring the reliability of the use of new fluorescent materials, the cost of materials and manufacturing is not increased. For example, Yimei Core Light Guangzhou Guangya Exhibition in 2017 launched a series of products that use blue light to excite a variety of phosphors to achieve Sunlight-like full spectrum. This kind of full spectrum LED light source is based on the above considerations, taking into account the light efficiency, light quality, cost and health lighting products. A special wavelength blue LED chip is used to excite red, green, cyan and other phosphors to realize a white light source with adjustable spectrum. By optimizing the wavelength and power of the chip and the formula of absorption and release spectra with fluorescent materials, the spectral continuity, color saturation and color rendering index of the illuminated LED light source are greatly improved. At the same time, the blue light is absorbed by the blue phosphor, and even secondary conversion is realized, which effectively reduces the proportion of blue light. Many LED packaging companies are also accelerating the development of full spectrum illumination LED light source stimulated by blue light. Recently, Laminas, Ultimate Core Light, Ruifeng, Jufei and other products have been launched.——LED Bulb Light
Relying on the continuous research and development of new fluorescent materials and LED chips reasonable proportion, optimize the light source spectrum, while introducing intelligent control system, in order to achieve a real sense of healthy green ecological lighting. Due to the different needs of lighting subdivision applications, light source providers can balance and optimize light efficiency, color requirements, fingering parameters, health indicators, and costs. For example, enterprises have developed different series of products for different application fields, such as universal full spectrum pleasant, full spectrum LED for eye protection lamp (Fig. 5), full spectrum LED for film and television lamp, etc.——LED Bulb Light
Since the beginning of this century, in a short period of 20 years, China's LED industry has achieved remarkable success, from a non-technology, scale-free industry to today's industry with complete industrial chain, advanced technology and the largest manufacturing scale in the world. Enterprises in the upper, middle and lower oil sectors have expanded from the Pearl River Delta to the Yangtze River Delta and other parts of the country, with growing scale and increasing international competitiveness. With the increasing competitiveness of the industry chain, the packaging pattern of LED devices is also changing. In recent years, the enterprising spirit of domestic manufacturers has been brought into full play. Both chip and packaging industries are expanding their production lines in tens of hundreds of units, while international manufacturers have not expanded their production in the past few years.——LED Bulb Light
In terms of production technology and equipment, the production line of LED packaging has changed from bird gun to gun. At present, most processes of LED packaging manufacturing line have been automated and are developing towards intelligent interconnection and automatic control technology. In terms of packaging structure, from the beginning of lead frame packaging to multi-chip array assembly, to today's DSP, flip-flop technology and the rising MIN LED, packaging technology is still developing rapidly under the impetus of market demand. In the aspect of device quality, with the commercialization of LED light efficiency reaching the peak of 180 lm/w, people gradually shift their focus from the device light efficiency to the higher requirements of light and color, and hope to meet the requirements of health and mood lighting while paying attention to energy saving.——LED Bulb Light
This white paper tries to analyze this magnificent LED light source industry from several aspects. It can only provide a useful reference for decision makers and product developers of enterprises, so as to see the direction of development of LED light source devices, to understand the gap between the highest technology in each link at present and abroad, and to understand the deep-seated demand for lighting products. Promote the development of LED entrepreneurship in China.——LED Bulb Light
Eye-pleasing Series: It has the characteristics of restoring the real and vivid color of objects. It takes into account the indicators of high color rendering/low energy blue light/high light efficiency/low cost. It is a universal 98-finger LED, suitable for business/education/medical/art exhibition hall/home, etc.——LED Bulb Light
Full spectrum eye protection lamp series: Considering the difference of eye structure and light transmittance, sensitivity and adults of growing children, the ability to withstand blue light is relatively weak. For lamp with long time, close distance and illumination requirement, attention should be paid to the possible damage of high energy blue light component to retina. As shown in Fig. 5, through the unique design of LED light source, the proportion of short-wave high-energy blue light is further reduced on the basis of the high-display and eye-pleasing series. At the same time, the proportion of high-band blue light is guaranteed to promote work enthusiasm and focus, and improve learning and work efficiency.——LED Bulb Light
Full Spectrum Film and Television Lamp Series: Except for high color rendering, it meets the challenge that R1-R15 is all greater than 90, and has excellent fidelity and color saturation. Higher consistency index of TV lighting (TICL=99) makes the color of the output pictures of TV cameras and cameras real, clear and vivid.——LED Bulb Light
Full spectrum technology is not limited to a specific packaging form. It can be packaged into SMD, COB, Flash, DOB module products according to different application requirements, providing a variety of flexible LED beads and solutions for high-quality lighting life.——LED Bulb Light
CTO of Liu Guoxu Yimei Xinguang (Beijing) Technology Co., Ltd.
Consultant of Light Source Devices for Aladdin Lighting Industry Research White Paper 2018