LED Street Lamp Design Requirements

- Jun 10, 2019-

1. The biggest characteristic of lighting LED is the function of directional emission of light, because power LED is almost equipped with reflector, and the efficiency of this reflector is significantly higher than the efficiency of the lamp reflector. In addition, LED light efficiency detection has included the efficiency of its own reflector. Road lamps using LED should make the best use of the characteristics of directional emission of LED light, so that each LED in the road lamps directly shine light to each area of the road being illuminated, and then use the auxiliary light distribution of lamp reflector to achieve a very reasonable comprehensive light distribution of road lamps. It should be said that road lamps and lanterns should really meet cjj45-2006 and CIE31 and CIE115 standard illuminance and illuminance uniformity requirements, lamps and lanterns should include three times of light distribution function to better achieve. And LED with reflector and reasonable beam output Angle itself has good primary distribution function. In the lamp, the installation position of each LED and the direction of emitting light can be designed according to the height and width of the road lamp. The reflector in this kind of lamp is only used as an auxiliary third 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. These adjustment means are unique to road lamps with LED light source. By making full use of these characteristics, the lighting power density can be reduced to meet the premise of the illumination and uniformity of the road surface, so as to achieve the purpose of energy saving.

2. The power supply system of LED street lamp is different from the traditional light source. The constant current drive power which is specially needed by LED is a cornerstone to ensure its normal work. How to make a group of tightly compressed LED security, is also an indicator to investigate LED street lights. The requirement of LED driving circuit is to ensure constant current output. Because the junction voltage is relatively small in the changing region when LED is working in the forward direction, the constant driving current of LED is guaranteed, and the constant output power of LED is basically guaranteed. For the current situation of unstable power supply voltage supply in China, it is very necessary for the driving circuit of road lamps and lanterns LED to have constant current output characteristic, which can ensure constant light output and prevent the LED from running at excessive power.

In order 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. Using the above two schemes can make the drive circuit still have high conversion efficiency under the premise of maintaining good constant current output characteristics

China's road lamps, the basic use of HID light source with trigger and inductance ballast mode, although this mode has low energy efficiency and strobe problems. When LED lamps with electronic drive circuit are used in field lighting, lightning induction is an important problem that threatens their plasticity.

As we all know, lightning in the sky emits a wide spectrum of radio waves, while overhead road lighting power lines are good to receive wireless. The radio waves emitted by the same lightning received by the two power lines are common mode interference signals for the drive circuit, which can be up to several hundred volts to several thousand volts to the ground. It is easy to break through the EMC grounding capacitance in the drive circuit or the small electrical gap between the ground (on the housing), 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 drive circuit of the LED with a quick-response piezoresistor to ensure the leakage of differential mode interference. Because the lightning induced interference is repeated many times, when the interference voltage is high, the piezoresistor instantaneous conduction and discharge current may be large, so the piezoresistor adopted should not only have the quick response ability, but also should have the instantaneous conduction and discharge ability of tens of amperes without damage. In addition to piezoresistor, the input end of LED drive circuit should also be combined with the protection of conducting interference (EMI), and a compound LC network should be designed, so that these LC networks can not only prevent the leakage of internal EMI to the power grid, but also significantly inhibit the interference signal of lightning.

In addition, the electrical gap between each point of the LED drive circuit to the ground should be maintained at more than 7mm, EMI protection of the grounding capacitor and the drive circuit to the ground insulation strength, should meet the requirements of the reinforced insulation (4V+2750V), this can make the LED drive circuit with good resistance to differential mode and common mode lightning induction ability.