Why LEDlamp glows after switch off?
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| Amazing effect of LED lamp |
Introduction
Why LED lamp glows after switch off? This is very common question in any competitive exam and interview. We find the reason scientifically and practically for this Amazing Effect of LED Lamp.
In a Led lamp are three part connector pins, driver circuit and LED cell. All parts are defined as their wattage rating. We know LED works only direct supply.
Circuit Description
But we use LED lamp in the AC supply .So we need a rectifier and an alternative Step Down transformer because if we use the Step Down transformer the system becomes very heavy. This Alternative arrangement is called Transformer less Rectification.
LED rectifier basically consists non polarized capacitor, diodes, Ferrite transformer Now some manufacturers don't use traditional diodes, a bridge IC DF 10 is used to make the PCB more compact. This is all the structural description of LED lamps.
Reason
Now describe what the reason is. Mainly two reasons for this to incident 1st one is the huge rate of capacitor when the pcb connects to Ac supply. Then the capacitor is charged up to full charging capacity.
When we turn off the LED lamp, the discharging time of the capacitor is not equal to charging time. Discharging is less than time compared to charging .The charging and discharging waveform shown below. At the Time of discharging the led lamp dimming gradually.
After some time it will take too much to completely off. Here some other reason is arise. Basically LED is diode it consist p type material and n type material and have junction barrier.
P type material takes holes and n type material takes free electrons. When capacitor charge then the free electrons pushed and cross the junction barrier and conduct with holes.*and the pulsed free electron energy released as from of light*.
So when discharging is incident the junction barrier acts as a capacitor and due to some kinetic energy is present in the electron some electron due to kinetic energy crosses the junction barrier and that energy releases a small amount of light.
As long as the kinetic energy is present, the electron will be in force. And light still glowing. This will actually cause the LED lamp to glow when you turn off the LED lamp. This incident doesn't depend on the price, quality, and wattage. If you buy any LED lamp which can be better price and quality you will see such incidents there too.
Conclusion
This effect is very natural for any LED lamp. This Effect is good for any LED lamp. It increases the long life. Every capacitor filtered device has same effect but cannot understand in any way. Some time many competitive exam or interview is common question now day.
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