What is the values of  the following integral:

$$\int_{w \in S^{n-1}} e^{i\lambda< x,w  >} dw.$$
where $\lambda\in\Bbb R, i^2=-1,x\in\Bbb R^n;<,>$ the inner product scalar on $\Bbb R^n$  and $S^{n-1}$ the unit sphere of $\Bbb R^n$.