如何在PyOpenGL中使整个场景的灯光变暗？

from OpenGL.GL import *
from OpenGL.GLUT import *
from OpenGL.GLU import *

def init():
    glEnable(GL_LIGHTING)  # 启用光照

    light_pos = [1.0, 1.0, 1.0, 0.0]  # 灯光位置
    light_ambient = [0.2, 0.2, 0.2, 1.0]  # 环境光照强度
    light_diffuse = [0.0, 0.0, 0.0, 1.0]  # 漫反射光照强度
    light_specular = [0.0, 0.0, 0.0, 1.0]  # 镜面反射光照强度

    glLightfv(GL_LIGHT0, GL_POSITION, light_pos)  # 设置灯光位置
    glLightfv(GL_LIGHT0, GL_AMBIENT, light_ambient)  # 设置环境光照强度
    glLightfv(GL_LIGHT0, GL_DIFFUSE, light_diffuse)  # 设置漫反射光照强度
    glLightfv(GL_LIGHT0, GL_SPECULAR, light_specular)  # 设置镜面反射光照强度
    glEnable(GL_LIGHT0)  # 启用灯光0

    glLightModelfv(GL_LIGHT_MODEL_AMBIENT, [0.1, 0.1, 0.1, 1.0])  # 设置全局环境光照强度

def display():
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
    glutSolidTeapot(1.0)  # 渲染茶壶模型
    glFlush()

def main():
    glutInit()
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH)
    glutInitWindowSize(400, 400)
    glutCreateWindow(b"PyOpenGL Lighting Example")
    glClearColor(0.0, 0.0, 0.0, 1.0)
    glEnable(GL_DEPTH_TEST)
    init()
    glutDisplayFunc(display)
    glutMainLoop()

if __name__ == '__main__':
    main()