"For the light enlightens every man who is progressing upwards in the cosmos."
This is the testimony of John concerning the Light of CHRIST. One way to tell if someone does not have this light is if they commit horrible sins (child abuse, murder, rape, etc). This means that such a person no longer has the influence of CHRIST in their life, and they consequently do the works that Satan would do to create maximum misery.
If you are not moving closer to GOD, you do not have the Light of CHRIST.