Question

An LED operates at 1.5 V and 5 mA in forward bias. Assuming an 80% external
efficiency of the LED, how many photons are emitted per second?

Answer 1

$P_{in} = η_{ext}\frac{i}{e}hf$

Number of photons $= \frac{P_{in}}{hf} = η_{ext}\frac{i}{e}$

Number of photons $= 0.8 \times \frac{5 \times 10^{-3}}{1.6 \times 10^{-19}}$

Number of photons $= 2.5 \times 10^{16}$