Amplitude of electric field in a parallel beam of light of intensity $8w/m^2$  is

$I=\frac{1}{2}{\epsilon }_0{E}_0^{2}c\Rightarrow E_0=\sqrt{\frac{2I}{{\epsilon }_{0}C}}=\sqrt{\frac{2\times 8}{8.85\times {10}^{-12}\times 3\times {10}^8}}N/C=77.62N/C.$