I am writing a very simple directional light shader and I want to pass in my own light position coordinates (treated more like a directional light) instead of using gl_LightSource[0].position. I've been searching around and couldn't find any clear explanation on how to store my light position coordinate into eye space coordinates.

I've tried multiplying my vector with gl_ModelViewMatrix in the shader, and I've tried doing it on the CPU side but still can't produce the same result as gl_LightSource[0].position.

The light position (or direction rather) is (-1, 0, 0)

vertex shader:

Code :
varying vec3 vertex_light_position;
varying vec3 vertex_normal;
uniform vec3 light_position;
void main() {
    gl_FrontColor   = gl_Color;
    gl_Position     = gl_ProjectionMatrix * gl_ModelViewMatrix * gl_Vertex;
    gl_TexCoord[0]  = gl_MultiTexCoord0;
    vertex_normal = normalize(gl_NormalMatrix * gl_Normal);
// using my own light position coordinate
    vertex_light_position = normalize(light_position);
// old version
    //vertex_light_position = normalize(gl_LightSource[0].position.xyz);

So basically my question is how do I properly store my vector into eye space coordinates?
I appreciate anyone taking the time to explain this to me. Thanks