Question

A 4W LED has an efficiency of 0.90. what is the power of the light emitted

Answer 1

The power of the light emitted is 3.6 W

Explanation:

The efficiency of an electric device is defined as follows:

$\eta=\frac{P_{out}}{P_{in}}$

where

$P_{out}$ is the output power

$P_{in}$ is the input power

For the LED in this problem, we have

$P_{in}=4W$ is the power in input

$\eta=0.90$ is the efficiency of the LED

Re-arranging the equation and substituting the numbers, we can find the power output, which is the power of the light emitted:

$P_{out}=\eta P_{in}=(0.90)(4)=3.6W$

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