LED brightness adjustable function is very important in LED lighting, but also the segment need to be great taked care in LED lamp and LED display.The following MCPCB manufacturers will analyze the principle of LED self dimming lighting system.
The technical principle of LED self regulating lighting system
The LED self dimming system is designed and developed according to the dynamic characteristics of public lighting and the concept of “on-demand lighting”.It integrates three parts of pyroelectric infrared mobile detector, dimmer controller and LED light source, and realizes the mute control of luminance in the lighting place. When a person (car) activities in the vicinity of lamps and lanterns, lamps installed on the pyroelectric infrared motion detector transmits collected signals to the dimming controller, dimming controller according to the received signal, control LED light brightness, and delay time.
If the delay time is exceeded, the detector can not capture the signal of human activity, and the LED light source will be changed from bright to low (or out of). If the delay time detector can still collected human activities (car) signal, LED light source will continue to maintain high, thus ensuring the premise of not reducing lighting quality, greatly reduce the “invalid lighting” time, the public places “on-demand lighting, energy-saving effect is very obvious.
Because every day in between bright and low light energy, and most of the time in the low light, bright day time lightning is less than four hours, to avoid the phenomenon of light LED light source long time high current generated by high temperature, so the LED light source is very small, prolonged service life.
LED main dimming method
The dimming function for incandescent lamp can achieve lower costs, along with the development of LED lighting products, LED lighting in the conversion can be reluctant to lose the advantages of dimming control, LED lamp dimming method mainly, there are three kinds of common, these three kinds of dimming skills are according to the change of LED drive the current input to the dimming. In accordance with different circuit systems can also be divided into analog dimming and PWM dimming.
The first: the dimming dimming method for driving current through the modulation of LED to complete the LED lamp, the brightness and LED chip LED drive current into a certain proportion, so we adjusted the LED drive current control LED lamp brightness can be.
The second type: the dimming method is called analog dimming or linear dimming. The advantage of the dimming method is that when the driving current increases linearly or decreases, the influence of the drive current overshoot on the life of the LED chip is reduced, and the anti disturbance performance of the dimming circuit is stronger. The defect is that the size of the driving current changes, which definitely affects the color temperature of the LED chip.
Third: This dimming method is called pulse width modulation (PWM). This method is by adjusting the drive current is undulate, the pulse width of the variable, after the change of the pulse width modulation for LED light modulation of continuous light time, also changed the input power, so as to achieve the goal of energy saving, dimming. The frequency is about the same as usual, about 200Hz~10KHz; because of the visual lag of the human eye, the light produced by the light source in the dimming process will not be perceived. The advantage of this dimming method is that it can improve the heat dissipation performance of LED, and the defect is that the drive current overshoot affects the life of LED chip.
In general, analog dimming can usually be done very simply. However, due to the characteristics of the LED light, the average driving current will be shifted. For monochromatic LED, the primary wavelength changes. For white LED, the associated color temperature (CCT) changes.
Dimming with PWM ensures that the LED sends out the colors that the designer needs. PWM dimming can also improve output current accuracy. Analog dimming using linear modulation reduces the accuracy of the output current. Generally speaking, PWM dimming can be more accurate than linear control light output relative to analog dimming
In terms of energy saving, there is no comparability. Because PWM ensures the current (light intensity) under CCT and color conditions, analog dimming does not exist. If you want to sacrifice this premise to consider energy saving, you need the actual data. But it is estimated that PWM will have an advantage in achieving the same illuminance. From the dimming response time, the PWM dimming is faster because of its response and enables more precise dimming. It is widely used in practical use.
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