Light source attributes are set by glLight.
A light source has a position and a color.
The intensity of the light is simply the intensity of the color.
glEnable(GL_LIGHT0)
glLightfv(GL_LIGHT0, GL_POSITION, [0, 1, 0, 0])
glLightfv(GL_LIGHT0, GL_DIFFUSE, [1, 1, 1, 1])