# Difference between an absorbance, emission, and excitation spectrum for uv-visible spectroscopy

From the list below, circle the wavelength that would be the best setting for the UV-visible spectrophotometer used to determine the FITC concentration in the sample.
$$\begin{array} {} \mathrm{wavelengths:} & \pu{400 nm}& \pu{450 nm}& \pu{500 nm}&\pu{550 nm} &\pu{600 nm} \end{array}$$

The exam paper answer is $$\pu{500 nm}$$, because we need the wavelength of "maximum absorbance." But this graph shows two curves, and the absorbance curve is omitted.

But what is the difference between an emission, absorbance, and an excitation spectrum? What are they measuring? How do you interpret/read these graphs - those with multiple curves.