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How do you know the voltage of an LED?

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By multimeter
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After connecting led to a DC source we can measure the voltage of led by connecting a voltmeter across it. 

But voltage rating of the led is given by the manufacturers. Or we can test it by observing the intensity of led. Basically there are 1.5 v, 5v.... are available in the market

For more doubts connect with me in linkdin

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