Calculating energy level from wavelength
All you need are two equations and two constants (speed of light and Planck constant):
\begin{eqnarray}
\mathrm{E} &amp; = &amp; h\nu\\
h &amp; = &amp; \mathrm{6.62606957 \cdot 10^{−34}   J\cdot s}\\
\mathrm{c} &amp; = &amp; \lambda\nu\\
\mathrm{c} &amp; = &amp; 299792458\ \mathrm{m\cdot s}^{-1}\\
\end{eqnarray}

Using these data, the energy of a photon with $\lambda = 350\ \mathrm{nm}$ calculates to:

$$\mathrm{E} = \frac{6.62606957 \cdot 10^{-34} \cdot 2.99792458 \cdot 10^8}{350 \cdot 10^{-9}} \cdot \frac{\mathrm{J \cdot s \cdot m}}{\mathrm{s \cdot m}} = 0.05676 \cdot 10^{-17} \mathrm{J} = 5.676 \cdot 10^{-19} \mathrm{J}$$

This is the energy difference to the higher level.