opengl里为什么打了灯光后文字显示不出来？求教！

最近在用opengl做一个3d游戏。没打灯光前，场景中的文字是可以显示的。可是打了灯光后就显示不出来了。求高手指点！
以下是我游戏场景渲染的函数
void GameStage::Draw()
{
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        float lightAmbient[] = {0.8,0.7,0.75,1.0};
float lightDiffuse[] = {0.8,0.7,0.75,1.0};
float lightPosition[] = {75.0,10.0,65.0,0.0};
        float lmodelAmbient[] = {0.5,0.5,0.5,1.0};
        glShadeModel(GL_SMOOTH);
        glLightfv(GL_LIGHT0,GL_AMBIENT,lightAmbient);
        glLightfv(GL_LIGHT0,GL_DIFFUSE,lightDiffuse);
        glLightfv(GL_LIGHT0,GL_POSITION,lightPosition);        glLightModelfv(GL_LIGHT_MODEL_AMBIENT,lmodelAmbient);        glEnable(GL_COLOR_MATERIAL);        glEnable(GL_LIGHTING);
        glEnable(GL_LIGHT0);
        glEnable(GL_DEPTH_TEST);        Stage::Draw();

        mFont->Print("just a test!");
}