Led street lamp design requirements

- May 22, 2019-

1. The biggest characteristic of LED for lighting is the function of directional emission, because almost all power LED are equipped with reflectors, and the reflector efficiency is significantly higher than the reflector efficiency of lamps. In addition, LED light efficiency detection has included the efficiency of the reflector. Road lamps using LED should make full use of the characteristic of directional emitting light of LED, so that each LED in road lamps can direct the light to each area of the road surface, and then use the auxiliary light distribution of lamp reflector to realize the reasonable comprehensive light distribution of road lamps. Should say, road lamps and lanterns should accomplish the illuminance that accords with cjj45-2006 and CIE31 and CIE115 standard truly and illuminance evenness requirement, the function that luminaire should contain 3 times to distribute light inside ability is better realized. And LED with reflector and reasonable beam output Angle itself has a good light distribution function. In the lamp, it can design the installation position of each LED and the direction of emitting light according to the height of the lamp and the width of the road so as to achieve a good secondary light distribution function. The reflector in this type of luminaire only serves as an auxiliary third-time light distribution means to ensure better uniformity of road illumination.

In the design of the actual road lighting lamps and lanterns, can be used in the basic set up at an LED beam direction under the premise of the each LED with spherical universal joint on the lamps and lanterns, when used in lamps and lanterns of different width, height and irradiation can be adjusted by the spherical universal joint make every LED irradiation direction to achieve satisfactory results. In determining each LED output power and beam Angle, according to E (lx) = I (CD)/D (m) 2 (light intensity and illumination distance inverse square law), were calculated for each LED in the basic output light beam Angle when selected should have the power, and by adjusting the output power of each LED and LED driver circuit to the power of each LED different to keep every LED light output reaches expected value. All these adjustment methods are unique to road lamps with LED light source. By making full use of these features, the lighting power density can be reduced on the premise of satisfying illumination and uniformity of illumination of road surface, so as to achieve the purpose of energy saving.

2. The power system of LED street lamps is also different from that of traditional light sources. The constant-current driving power specially required by LED is a cornerstone to ensure its normal operation. How to make a compact set of LED safe is also an indicator to examine LED street lights. The requirement of LED for driving circuit is to ensure the characteristics of constant current output, because the junction voltage is relatively small when the LED is working in a positive direction, so the drive current of LED is guaranteed to be constant and the output power of LED is basically guaranteed to be constant. For the current situation of unstable power supply in China, it is very necessary for the drive circuit of road lamps LED to have constant current output characteristics, which can ensure the constant light output and prevent LED from running at excessive power.

To make the LED drive circuit present constant current characteristics, the output internal impedance must be high when viewed from the output end of the drive circuit. At work, also through this output impedance load current, if the drive circuit by step-down dc constant current source circuit, rectifier filter after or general switch power resistance circuit, on its must also consume a lot of active power, so the two types of drive circuit in the basic satisfy the premise of constant current output, high efficiency is impossible. The correct design scheme is to use active electronic switching circuit or high frequency current to drive the LED. The two schemes mentioned above can make the drive circuit still have high conversion efficiency under the premise of maintaining good constant-current output characteristics

Most of the road lamps and lanterns in our country adopt HID light source with trigger and inductive ballast mode, although this mode has some problems such as low energy efficiency and stroboflash. LED lamps with electronic driving circuits, when used in outdoor lighting, threaten the plasticity of an important aspect of lightning induction.

As we all know, the lightning in the air is the transmission of a broad spectrum of radio waves, and overhead road lighting power supply lines, is a good reception of wireless. The same lightning wave received by two power lines is a common mode interference signal for the drive circuit, which can be hundreds of volts to thousands of volts on the ground. It is easy to break through the EMC grounding capacitance or small ground (to the shell) electrical gap in the drive circuit, causing damage to the drive circuit.

Another due to the power supply circuit is three phase four wire system neutral grounding the polarity of the power and so on overhead power line two paragraphs, at the instant of the induction to the lightning radio waves, due to two different root the instantaneous impedance of the power supply line to ground and make the two power supply line between a differential mode interference voltage, also this moment time mode interference voltage can reach hundreds of v to 3000 v, the voltage tends to breakdown drive circuit of power rectifier diode and printed circuit board on the clearance between different electrode polarity, damage of the LED controller will also make the drive circuit.

To solve this problem, it is necessary to connect the input end of the LED drive circuit with a quick response varistor to ensure the release of differential mode interference. As the inductive interference of lightning is repeated for many times, when the interference voltage is high, the current of the piezoresistive instantaneous conduction and discharge may be very large, so the piezoresistive adopted should not only have the quick response ability, but also have the discharge ability of instantaneous conduction and dozens of amperes without damage. In addition to the use of piezoresisors, the input end of the LED drive circuit should also be combined with the protection of conducted interference (EMI) to design a composite LC network, so that these LC networks can not only prevent the leakage of internal EMI to the power grid, but also play a significant role in inhibiting lightning interference signals.

In addition, the electrical gap between each point of the LED drive circuit to the ground should be kept above 7mm. The grounding capacitance of EMI protection and the ground insulation strength of the drive circuit should meet the requirements of reinforced insulation (4V+2750V), so that the LED drive circuit has good resistance to differential mode and common mode lightning induction.