GLSL Passing Additional Light Positions in As Uniform Variables to Vertex Shader

Assuming you want to pass in additional light positions to the vertex shader (outside of the lights provided by the fixed functional pipeline) I am not seeing these additional uniforms functioning correctly.

For example in my vertex shader I have:

...
uniform vec3 light_pos;

...
varying vec3 frag_light_pos;

void main() {
    ...

    frag_light_pos = vec3(0.0f, 100.0f, 0.0f);
    //frag_light_pos = light_pos;

    ...
}

Where the difference in my scene can be seen below.

To set the uniform variable I am using Qt's QOpenGLShaderProgam::setUniformValue in the following manner.

QVector3D light_pos(0.0f, 100.0f, 0.0f);
m_ShaderProgram->setUniformValue("light_pos", light_pos);

All my other uniforms, the mv, mvp, and (trans(mv))^-1 all work so it is not a problem with Qt. Where am I going wrong? I would expect to see the same image using either version.

Screenshot using const vec3:

Screenshot using uniform vec3: