Can you tell me if there is any difference between these 2 units?

$\log \mathrm{quanta/cm^2/s}$ vs $\log \mathrm{photons/cm^2/s}$



"Number of photons" and "Number of quanta" are both dimensionless so

"quanta" cm$^{-2}$ s$^{-1}$ has the same units as "photons" cm$^{-2}$ s$^{-1}$.

But strictly, both expressions are wrong since:

$\log{x}= (x-1) - (1/2)(x-1)^2 + (1/3)(x-1)^3 - (1/4)(x-1)^4 + ...$

So the argument inside the logarithm should be unit-less.

  • $\begingroup$ Note that $\log(a/b)\equiv\log(a)-\log(b)$, so it is possible for units to be present in the argument of logarithms, though care needs to be taken (I believe there is a PSE post on the use of units in log) $\endgroup$ – Kyle Kanos Jul 3 at 14:33

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