Question

A $100W$incandescent lightbulb emits about $5W$of visible light. (The other $95W$are emitted as infrared radiation or lost as heat to the surroundings.) The average wavelength of the visible light is about $600nm$, so make the simplifying assumption that all the light has this wavelength. How many visible-light photons does the bulb emit per second?

Short answer

The visible-light photons bulb emits per second is $1.51\times {10}^{19}\frac{photons}{s}$.

Step-by-step solution

Given Information

We have to given an incandescent lightbulb that emits about $5W$of visible light and the average wavelength of the visible light is about $600nm$.

Simplify

We can start the solution with the expression for the rate of emission of photons:

$\begin{array}{rr}R& =\frac{P}{hf}\\ f& =\frac{c}{\lambda }\\ R& =\frac{P\lambda }{hc}\\ R& =\frac{5\cdot 600\times {10}^{-9}}{6.63\times {10}^{-34}\times 3\times {10}^8}\\ R& =1.51\times {10}^{19}\frac{photons}{s}\end{array}$