We need frequency:-
[tex]\\ \rm\Rrightarrow \nu=\dfrac{c}{\lambda}[/tex]
[tex]\\ \rm\Rrightarrow \nu=\dfrac{3\times 10^8m/s}{590\times 10^{-9}m}[/tex]
[tex]\\ \rm\Rrightarrow \nu=0.0051\times 10^{17}Hz[/tex]
[tex]\\ \rm\Rrightarrow \nu=5.1\times 10^{14}Hz[/tex]