14.55 · (σκοτόομαι[a]) · Physical Events and States · Darkness

to become dark (derivative of σκότος[a] ‘darkness,’ 14.53) to change from a condition of being light to one of being dark In REV 9:2 it may not be difficult to speak of ‘the air becoming dark,’ since this would mean the space above the earth, but it may be difficult to speak of ‘the sun becoming dark.’ In the latter instance, for both REV 9:2 and MAT 24:29, one may say ‘the sun will no longer shine’ or ‘the sun will not give its light.’
In place of ‘the air became dark,’ it is also possible to speak of ‘the sky will become dark.’

REV 9:2 · REV 16:10

32.44 · (σκοτόομαι[b]) · Understand · Lack of Capacity for Understanding

to be incapable of perceiving, to not be able to understand (figurative extension of meaning of σκοτόω[a] ‘to become dark,’ 14.55) to become unable to perceive and thus unable to understand It is rare that one can combine the concept of ‘becoming dark’ with incapacity to understand or comprehend. Sometimes a parallel figure of speech may be employed by using an expression such as ‘to not be able to see.’ For example, in ROM 1:21 it is sometimes possible to translate ‘their foolish minds became unable to see the truth,’ and in EPH 4:18 it is sometimes possible to translate ‘they were not able to see with their minds.’

EPH 4:18