Photon flux from a light source

[spaghetti3451]

Homework Statement

What is the photon flux (photons/ m² s) at a distance of 1 km from a light source emitting 50W of radiation in the visible domain, with wavelength 6000 Angstroms.

Homework Equations

The Attempt at a Solution

Energy of one photon = hc/λ = 3.32 x 10^-19J.
So, number of photons per second = 50/3.32 x 10^-19 = 1.51 x 10^-20.
So, photon flux = 1.51 x 10^-20/4π(1000)² = 1.20 x 10¹³.

Is this correct?

 

[mfb]

1.51*10^-20 photons per second? I think that is a typo.

The approach is good, and the numbers look reasonable.

 

[spaghetti3451]

1.51*10^{-[/size][/color]20} photons per second? I think that is a typo.

Yeah! That is a typo!

The approach is good, and the numbers look reasonable.

Thanks!