How To Achieve Dimming LED street Lighting？
As a constant current source, LED can be dimmed inherently. "The current flowing through the LED lamp beads determines the output of light." Their brightness can be adjusted simply by controlling the energizing current of the layer of semiconductor material affixed to the substrate.
LED does not like the traditional light source, dimming and will not affect the efficiency and life of LED. In fact, dimming can reduce their operating temperature, thereby extending the life of the LED.
In addition, the dimming range of LEDs is wider than that of compact fluorescent lamps and high intensity discharge lamps. Compared to the compact fluorescent lamp 10% to 30% of the dimming (data from the American Electrical Manufacturers Association NEMA), high-intensity discharge lamp 30% to 60% of the dimming (data from the US lighting product information engineering NLPIP) , LED dimming can be done to achieve the full load below 1%.
Any LED device, if you want to make a replacement light source or LED lighting, need a drive in order to achieve dimming. Because LEDs are low-voltage DC sources, LEDs require an electronic driver to convert AC into usable and adjustable DC current. These drives are divided into two dimming modes. In the pulse width modulation (PWM) mode, the current through the LED is turned off at a very high frequency, "usually several thousand times per second," and the current through the LED is equal to the current average in the LED switching cycle. Reducing the LED's on-time can reduce the average current or the effective current, thereby reducing the brightness of the LED.
PWM and CCR have their own advantages and disadvantages. PWM application is more extensive, dimming range is wider, can do light output of 1% or less, and regardless of the LED in the rated current, maximum current, or zero current work, can avoid color bleaching phenomenon. Because PWM dimming uses fast switching on and off, it requires more sophisticated and more expensive electronic drive devices to generate enough high frequency current pulses to prevent flickering of the human eye.
CCR dimming is more efficient and simple because it requires a much simpler and cheaper drive device. Unlike PWM, CCR does not produce electromagnetic interference caused by high frequency switching EMI. In addition, the CCR allows the drive to be placed farther away from the light source, which is advantageous for replacing the light source with LEDs or for compact fixtures with limited internal space. However, CCR is not suitable for applications where the dimming requirement is less than 10%. "In very low current conditions, LED can not work properly, light output is not stable.