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Foreword: Energy-saving research on new light sources for tunnel applications has attracted industry attention, and energy-saving research on LED tunnel lights has made significant progress. Because LED is used in tunnel lighting according to the scientific research results of Ming Vision and intermediate vision theory, color rendering and illumination, LED lighting tunnels have been used in many important tunnel lighting projects in China. The application of LED tunnel luminaires in tunnel lighting projects has made breakthroughs, but there are still problems. For example, there are no specific design and construction specifications for tunnel luminaires with LED as the light source, and product performance is uneven.
This article will analyze the key technical indicators that need to be paid attention to in the LED tunnel lighting project, and hope to provide reference for the design unit and users.
Optical part LED light effect
The LED single-watt lumen output is the basic indicator for determining whether the LED tunnel light has practical value. According to the requirements of the actual use of the LED tunnel light, the single-watt lumen of the LED used for the LED tunnel light should reach 90 lumens. After the rapid development of LED luminous efficiency in 2006 and 2007, CREE, Lumileds, and Hong Kong Zhen Mingli and other famous brands have successively launched the latest LED models.
Secondary light distribution distribution pattern
At present, the common distribution patterns of light distribution include concentrating light distribution, side emission type light distribution, and Lambertian light distribution. Different application modes are applicable to different light distribution forms. For example, road lighting should use batwing type light distribution, and spot light should adopt concentrating type light distribution. Due to the particularity of tunnel lighting, the arrangement density of lamps in tunnel lighting is very high, so the secondary light distribution form of the lamps in tunnel lighting is different from general road lighting. In the tunnel illumination, the batwing type light distribution and the Lambertian type light distribution can meet the illumination uniformity requirement. This is mainly because the lamp distance in the tunnel illumination is relatively small. For example, the middle section of the domestic tunnel lighting project has only 5 Meter.
The Hong Kong Zhen Mingli 75 tunnel light uses the commonly used batwing light distribution in road lighting and tunnel lighting, while the domestic LED tunnel light is Lambertian light distribution.
Particularity of light distribution design
Although the requirements for the distribution pattern of light distribution in tunnel illumination are relatively loose, it is necessary to have a light distribution design. Since the light distribution design is based on the primary light distribution of the light source, different light source types have different distributions, and the corresponding light distribution design also changes. Therefore, although there are professional manufacturers of reflectors, lenses and manufacturers, the products they provide are only based on a certain kind of LED light source. Of course, they can only be suitable for a certain kind of LED light source. Moreover, the types of LED light sources are rapidly increasing. In addition to the replacement of LEDs, the reflectors and lenses must be updated. Therefore, the secondary light distribution design must be completed by the tunnel light manufacturer itself. However, there are not many manufacturers that can independently carry out light distribution design.
Choice of light distribution
Commonly used face types are: spherical, ellipsoidal, hyperbolic, parabolic, and free-form surfaces, among which free-form surfaces are the most widely used and the most widely used. In addition, planes are also used in light distribution, but the plane usually only plays a transitional role—expanding the light source, but not the true light distribution. For example, the light distribution of an LED tunnel light in China is to select the plane as the light distribution surface type, so the final light distribution is actually the light distribution of the LED. There is no strict secondary distribution in this LED tunnel light. Light.
Predicting the lighting effect
In order to predict the lighting effect and installation method of the luminaire in the tunnel lighting, it is usually necessary to simulate in the special lighting software according to the basic parameters of the construction site and the photoelectric test data of the luminaire (for example, the file in IES format). Analyze, evaluate the lighting effects of the fixtures, and determine the best parameters for the installation.
If the results of the simulation analysis are not satisfactory, then it is necessary to modify the light distribution design or adjust the power of the lamps. At present, Hong Kong Zhen Mingli has the ability to complete the entire process from light distribution design, optical grade mold making, photoelectric test analysis to engineering effect design and analysis.
Electrical parts
Power factor
Under the requirements of energy conservation and environmental protection, new standards for power supply efficiency are being announced around the world. For example, mandatory standards specific to power factor correction (PFC) or reduced harmonic currents require the emergence of IEC 1000-3-2.
At present, there are two main types of power factor correction: active power factor correction and passive power factor correction.
The active power factor correction has high precision and stable performance, and the PFC value can be up to 0.99; the passive power factor correction circuit is simple and low in cost. However, the disadvantages of passive PFC are also obvious: because many luminaires have size limitations, the huge inductance limits the practicality; in order to be universal, a line voltage range switch is required. Increasing the switch increases the risk of operational errors; the unregulated voltage rail increases the cost of the DC-DC converter after the PFC section and reduces efficiency. Tunnel lighting generally requires a large number of lamps, and the power consumption is huge. Therefore, power factor correction must be considered.
harmonic
Harmonics, as a type of interference, causes the grid to be "contaminated." In 1993, China promulgated the national standard “Power Quality: Utility Grid Harmonics†that limits the harmonics of power systems, and stipulated the harmonic voltage limits of public utilities and the allowable values ​​of harmonic current injected into the utility grid by users. Harmonics increase the heat loss of electrical equipment, interfere with its function and even cause faults, and harmonics can cause frequency interference interference to information systems. Because of the harmful nature of harmonics, the suppression of harmonics should also be considered in tunnel illumination.
However, at present, there are still many problems in the control of electrical parameters such as power factor and harmonics in the domestic LED tunnel lamp market.
Electromagnetic interference & electromagnetic compatibility
A good electronic product must ensure that it can work normally under the electromagnetic interference of other equipment, and that it does not cause electromagnetic interference to other equipment during operation - this is the electromagnetic compatibility we usually require. The level of electromagnetic compatibility design plays a key role in product quality and technical performance.
Electromagnetic interference generally falls into two categories: conducted interference and radiated interference. Conducted interference refers to the coupling (interference) of signals on one electrical network to another electrical network through a conductive medium. Radiated interference refers to an interference source that couples (interferes) its signal to another electrical network through space.
At present, the domestic LED tunnel light is not fully mature in electromagnetic interference and electromagnetic compatibility design, and the performance of different manufacturers is uneven.
Control System
In tunnel lighting, it is usually required to steplessly adjust the brightness of the lamp and the brightness of the hole based on factors such as the brightness outside the hole, the traffic volume in the hole, and the speed of the tunnel. Therefore, the driving power of the LED tunnel lighting fixture should be able to accept the dimming control signal and adjust the output current to adjust the LED luminous flux. In addition, due to the large number of lamps used in tunnel lighting. Therefore, it is necessary to establish a fault detection mechanism for the luminaire.
Hong Kong's True Mingli LED tunnel luminaires already have 256-level dimming control, LED anomaly detection, and abnormal power supply output voltage detection.
Heat dissipation
LED is a photoelectric device. At the current high-end LED of Hong Kong Zhenmingli NP7F12TW-C1Z1 series, the small part of the electric energy is converted into light energy during the working process. Most of the other electric energy is converted into heat energy, so that the LED The temperature rises. On the other hand, the lumen output of the LED decreases as the junction temperature of the LED increases, and the lifetime of the LED decreases as the junction temperature increases. Therefore, the heat treatment of LEDs is not directly related to the use effect and life of tunnel lamps.
At present, there are several main forms of heat dissipation for high-power LEDs: natural heat dissipation, forced cooling of the fan, and heat pipe technology. Natural heat dissipation utilizes natural convection and heat radiation. The addition of a fan to force heat dissipation mainly uses forced convection to achieve heat dissipation. Of course, the heat pipe heat dissipation mainly uses a heat pipe as a heat sink member. Natural heat dissipation has the lowest heat dissipation cost, reliable structure and easy to be waterproof, but the structure design of the lamp body itself is high; the fan is forced to dissipate heat quickly, but the cost is high, the noise is high, the waterproofing is difficult, the life is short; The components are stable, but the cost is high and not beautiful.
Therefore, several heat dissipation methods should give priority to the natural heat dissipation method. When natural heat dissipation is difficult to solve the problem, we will consider other heat dissipation methods. Take the Hong Kong Zhen Mingli 75 tunnel light as an example. This tunnel light is a natural heat sink.
Conclusion
The current technical requirements of LED tunnel lights in engineering practice mainly refer to the relevant specifications of tunnel lamps with high-pressure sodium lamps as the light source, and there is no relevant specification for tunnel lamps with LED as the light source. With the maturity of high-power LED technology , relevant specifications for various types of LED lamps, including LED tunnel lighting, need to be written as soon as possible.
At present, the development of LED tunnel lamps in China has made great progress, but it is still not fully mature. There is room for improvement in light distribution design, electromagnetic interference & electromagnetic compatibility, and luminaire efficiency. Requires the unremitting efforts of the majority of research and development personnel.
(Edit: Xiaotang)
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