The wave length of first member of Balmer series of a hydrogen atom is nearly 

(The value of Rydberg constant R = 1.08 × 10⁷m^–1)

The wavelenght of the spectral lines is calculated as 

$\frac{1}{\lambda }=R\left[\frac{1}{n_1^2}-\frac{1}{n_2^2}\right]$

For first line in balmer series , The electron jumps from n₁=3  to n₂=2

$\frac{1}{\lambda }=109577.8\left[\frac{1}{2^2}\frac{1}{3^2}\right]cm{ }^{-1}.$

$\lambda =6600A°$