Discerning the vision of the uncreated Divine Light of God (theoria), from Satan appearing as an angel of light, is not complicated. According to St John Climacus and patristics, in the first instance “the soul rejoices . . . [and the] Light of God is without form, white and brings peace to the soul.” In the second instance, however, “the body is afraid . . . [with the devil’s light having] shape and colour and disturbs the soul.” Gregory Palamas added that the uncreated Light “is united with man’s soul . . . [whereas] the light of the devil remains separate, illuminates from the outside, and being created, has shape, form and colour.”
It should be noted that the Devil and his demon-minions are particularly terrified of prayer from the heart, ceaseless prayer from the heart of the soul, the nous, as activated by the Holy Spirit. This precisely because such prayer stops us from sinning and leads us to effectively increase in holiness, along the pathway of deification and theosis: full union with God, that is the original aim of God the Father for mankind.
Met. Hierotheos. (2010). The science of spiritual medicine. Levadia, Greece: Birth of the Theotokos Monastery.