166. Man, however, is taught by enlightenment, because being taught and enlightened are predicated of the understanding; for the understanding, which is man's internal sight, is enlightened by spiritual light just as the eye or man's external sight is enlightened by natural light. Moreover, both are similarly taught; but the internal sight, which is that of the understanding, is taught by spiritual objects; and the external sight, which is that of the eye, is taught by natural objects. There is spiritual light and there is natural light; and both are alike in external but unlike in internal appearance; for natural light is from the sun of the natural world, and consequently in itself is dead, while spiritual light is from the Sun of the spiritual world, and consequently in itself is living. It is this spiritual light and not natural light that enlightens the human understanding. Natural and rational light* (lumen) is not from natural light but from spiritual light; and it is called natural and rational light (lumen) because it is spiritual natural.
 In the spiritual world there are three degrees of light, celestial light, spiritual light, and spiritual natural light. Celestial light is a flaming light with a reddish glow, and is the light of those who are in the third heaven. Spiritual light is a gleaming white light, and is the light of those who are in the middle heaven, while spiritual natural light is like the light of day in our world. This is the light of those who are in the lowest heaven, and also of those who are in the world of spirits, which is intermediate between heaven and hell; but in the world of spirits this light with the good is like that of summer on earth, and with the wicked like that of winter.
 It should be known, however, that all the light of the spiritual world has nothing in common with the light of the natural world; they differ as what is living and what is dead. From these circumstances it is clear that it is not natural light, such as that before our eyes, that enlightens the understanding, but spiritual light. Man does not know this, because hitherto he has known nothing about spiritual light. It has been shown in the work HEAVEN AND HELL (n. 126-140), that spiritual light is in its origin Divine Wisdom or Divine Truth.
* The Latin word (lumen), thus in brackets, is used to refer to the natural light of man's own intelligence, as distinct from spiritual light, and the physical light of the material world, for both of which the Latin word is lux.