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## Homework Statement

The average wavelength that LED emits is 500nm. The electrical power of the LED is 300mW and the efficiency of turning energy into light is 66%. Number of emitted photons in unit time is?

## Homework Equations

##E_f=hcf##

##\frac{Pt}{E_f}=number of photons##

## The Attempt at a Solution

After calculating the energy of one photon i am to find the overall energy that is transformed into light. The energy is ##300x10^{-3}J## but how am i to include the efficiency? Just multiply the Energy with 0.66 and use that in the equation? The answer is suppose to yield ##5x10^{17} per second##