# Plank's law - my computer is having trouble with the formula

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Plank's law -- my computer is having trouble with the formula

$$f_\lambda \left( T \right) = \frac{{2\pi hc^2 /\lambda ^5 }}{{\exp \left( {\frac{{hc}}{{\lambda kT}}} \right) - 1}}$$

I'm guessing this thing wants wavelength in meters. So for a temperature of 5600 K and a wavelength of 0.5 um (5e-7 m), the part that I'm using as the exponent for e, $${\frac{{hc}}{{\lambda kT}}}$$ comes out to (6.626068e-24*2.99792458e8/(5e-7*1.3806503e-23*5600)) =51384823425.8871.

And e^51384823425.8871 is not a number my computer can calculate.

How can I use this formula?

Not a complete solution- but worth trying.
ln(f(T))=ln(2pi h c^2/lambda^5)-hc/lambda k T

Accurate to a lot of sig. fig.

Compare the magnitude of the two terms on the RHS to see if one dominates by orders of magnitude.