adding lens flare in OpenGL

I want to create a lens flare in OpenGL C++. I referred this video and star rendering code.

double calculateGlowSize(double diameter, double temperature, double distance) {
    static const double DSUN = 1392684.0;
    static const double TSUN = 5778.0;

    // Georg's magic formula
    double d = distance; // Distance
    double D = diameter * DSUN;
    double L = (D * D) * pow(temperature / TSUN, 4.0); // Luminosity
    return 0.016 * pow(L, 0.25) / pow(d, 0.5); // Size
}

but i want the output to be more like the image shown below.

How do i create a lens flare effect?