Irradiance environmental maps are an effective technique to render diffuse objects in arbitrary lighting environments. Based on current computer graphics hardware a technique is proposed for calculating irradiance environmental maps using vertex shader. The approach starts from an analysis of spherical harmonics and finds out a quadratic polynomial form of environment mapping. Using vertex shader instructions the polynomial coefficients and spherical harmonics functions can be fast calculated

and then the corresponding irradiance environment maps are also generated. When the lighting environment changes

the lighting coefficients are fast computed by generating a mipmap of the source environment map

so that real time recalculating irradiance environment is obtained. The experimental result shows it not only renders realistic lighting but also satisfies the interactive requirements in dynamic lighting environments.