Number of emitted photons per second

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 $5x10^{17} per second$

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Homework Equations

$E_f=hcf$
First, this must make no sense. The correct one should be $E=hf.$
Since you can get the energy of a photon, then given the amount of light you can calculate the number of the photons. Like what you said, the energy transferred to light per second is $300mJ\cdot 66\%.$

First, this must make no sense. The correct one should be $E=hf.$
Since you can get the energy of a photon, then given the amount of light you can calculate the number of the photons. Like what you said, the energy transferred to light per second is $300mJ\cdot 66\%.$
Yeah, your right, i havent seen that ive put $c$ there, thanks.
Well then, $\frac{E_t}{E_f}=\frac{198*10^{-3}J}{hf}$
$f=\frac{c}{w}=6*10^{14}$ yes the rest is clear thanks :)