0 Preface
In recent years, LED technology has continued to develop and the market is expanding at an alarming rate. LED's long life, small size, high brightness and other characteristics make it widely penetrate into a large number of applications, and maintain the momentum of rapid development. At the same time, as the luminous efficacy of LEDs continues to increase, the brightness continues to increase, and the power ranges from watts to tens of watts. People are gradually paying attention to the photobiosafety of LED products during use. Assessing the safety of products and making scientific and rational use can open up new application areas and improve people's quality of life while meeting safety requirements.
1 The emergence and significance of photobiosafety standardization
Light not only brings light to human beings, it creates a safe working environment and a comfortable living environment, and the radiation it produces can also cause harm to the human body. The damage mainly occurs in the eyes and skin of the human body and is divided into three categories: skin heat hazard, photochemical hazards of the skin and eyes, and near-ultraviolet hazards of the retina. As far as the performance of LEDs is concerned, due to the low brightness, the application is limited, and the direct harm caused by LEDs to the human eye is minimal. However, nowadays, the brightness of LEDs continues to increase, and people pay more attention to the safety of emitted light. Due to the particularity of the LED spectrum, it is necessary to consider the aspect of the LED as the light source, and also consider whether it meets the aspects of laser safety. Only by considering both of them is the safest for the user, and it is us. The purpose of setting safety standards. International standards for LED safety are CIES009E: 2002 and IEC60825.
The International Commission on Illumination (CIE) classifies LEDs as luminaires, defined as ductile (rather than point) sources that typically have a broad divergent beam. The Technical Committee TC6-55 of Part 6 (Photobiology and Photochemistry) in CIE is considering different ways to assess the photobiosafety of LEDs. Among them, the standard limits the exposure limits of LEDs to photochemical hazards of skin and eyes, near-ultraviolet hazards of the eyes, retinal blue photochemical hazards, retinal aphakic photochemical hazards, retinal thermal hazards and skin thermal hazards. Values ​​are based on the corresponding guidelines of the ICNIRP (International Commission for the Prevention of Non-Ionizing Radiation). CIES009E: The 2002 standard recommends that manufacturers use the categories of exempt, low and medium hazard to define LED products.
The International Electrotechnical Commission (IEC) uses the IEC60825 series of standards for the safety of laser products to evaluate the photobiosafety of LEDs and classify LEDs into laser products. IEC60825-1 "Safety of Laser Products Part 1 Equipment Classification, Requirements and User's Guide" has a dual limit of 400nm and 600nm (thermal and photochemical aspects). At shorter wavelengths below 400 nm, a large amount of UV light is absorbed by the cornea and/or lens, which in turn can cause damage. IEC60825-1 is graded according to the laser (or LED) reachable emission limit (AEL), which is used to indicate the degree of danger of laser (or LED) light. Level 1 is safe, and most LED products fall to level 1, or do not need to be rated. LEDs and laser products are not subject to IEC60825-1 if they are not exposed to Class 1 under all conditions of operation, maintenance, service and failure.
2 Comparison of CIE and IECLED photobiosafety standards
2.1 Comparison of CIEIEC Exemption Limits
The IEC is more stringent than the CIE in the yellow-green to red-light region; on the contrary, the CIE is more stringent than the IEC for the exposure limits in the blue-green and white regions.
2.2 Retinal blue light damage
This type of hazard is mainly caused by blue light and white light. For the same exposure event, the study found that the IEC laser standard and the CIE source standard are very consistent in the exposure limits of the blue region. However, the IEC laser standard defines that blue light hazards occur at wavelengths above 400 nm, while CIE broadens to a minimum of 380 nm.
2.3 Retinal visible range damage
The exposure limits defined by the CIE and IEC hazards in the visible range are 3.2 times different.
2.4 Near infrared hazard
In addition to the retinal thermal hazard exposure limits, CIE has added an additional two types of ratings for the infrared range of wavelengths greater than 780 nm than the IEC: LV (retinalthermalhazardofsourceswithlowvisualstimulus) low visual stimulus source of retinal thermal hazard and CL (cornealenshazard) Corneal lens damage.
Due to the complexity of the practical application of LED, it is not completely a laser series, but also different from the traditional light source. LED needs a scientific and applicable special LED light safety standard to meet the development needs of the LED industry. Moreover, the situation that causes eye damage under LED illumination can be very complicated. For example, in some cases, the most harmful observation point may be some distance away from the light source instead of the nearest point. In addition, the determination of the performance of the light source also plays an important role in the correct evaluation of the biosafety of the LED light.
3 The special role of blue LEDs in the biological system
Since the artificial light source, humans can decide their own work schedule autonomously, and lighting has freed us from the limitations and constraints of darkness. With the development of science and technology, the contribution of light has only gradually penetrated into various fields of people's life. At the same time, human requirements for light are no longer limited to brightness, but the requirements for the impact of light on human health and quality of life are more demanding. harsh. As a result, research on the biological function of light has been intensified, including the biological function of blue light—improving the quality of people's work and life.
Usually, when studying the effect of light on the human eye, the most attention is the cone-shaped and columnar photoreceptor cells on the retina, which play a role in both visual and dark vision. Cones are most sensitive to light with a wavelength of 555 nm, while the maximum sensitivity of column cells occurs at 507 nm. These are the visual system effects given by the light we usually know. The biological function described in this paper is a new photoreceptor cell, discovered by David Berson of Brown University in the United States, called the Sichen vision system (non-imaging vision), its maximum sensitivity is near the wavelength of 460nm blue light and directly acts on the lower The pineal gland of the thalamus affects the biological function of the human body.
Figure 1 Spectral sensitivity distribution of the visual effects of Category 3
Nowadays, in developed regions, more and more people work irregular hours. For example, the “three shifts†of people, long-term or intermittent day and night upside down working hours will bring discomfort to the human body, reduce work efficiency, and even more It affects the normal physiological cycle, leading to diseases such as neurasthenia. The application of blue light illumination can stimulate the ganglion cells on the retina, increase the concentration of cortisol in the body, and inhibit the secretion of melatonin, which can significantly change the original unsuitable state. To achieve the same biological effect, the illumination required to use other colors of light is higher. In 2004, Cajochen found that after illuminating with 460nm monochromatic light for 2 hours, it showed more obvious melatonin inhibition than 555nm monochromatic light irradiation, and also increased alertness, increased body temperature, heart rate, and reduced temperature in the skin tip area. In addition, the latest CIE study shows that the lack of blue light pulse irradiation can reduce melatonin inhibition, but may cause the clock to shift. Among many light sources, LEDs are more suitable for related applications because conventional light sources do not easily obtain a narrow spectrum and need to avoid excessive heat radiation.
From the above, we can see the important effect of LED photobiological function. Therefore, it is necessary to combine security considerations and adopt scientifically appropriate application methods.
4 Conclusion
Unlike other traditional light sources, LEDs are a new kind of light source with great development potential. The problem of LED light biosafety has also become a new concern, both an opportunity and a challenge. The correct evaluation of the biosafety of LED light and its biological effects promote each other and complement each other.
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