Exegesis:

skopei oun mē to phōs to en soi skotos estin ‘consider, then, whether the light in you is not darkness,’ or, ‘be careful lest the light in you be darkness,’ preferably the former since estin is in the indicative.

skopeō ‘consider,’ ‘look out.’

skotos ‘darkness,’ here used emphatically instead of the adjective skoteinos.

Translation:

Be careful lest, preferably, ‘consider whether,’ ‘think (carefully) whether,’ ‘ask yourself whether perhaps.’

The light in you, or, ‘the light you have in you,’ ‘what is bright about you’ (Nieuwe Vertaling).

Quoted with permission from Reiling, J. and Swellengrebel, J.L. A Handbook on the Gospel of Luke. (UBS Handbook Series). New York: UBS, 1971. For this and other handbooks for translators see here . Make sure to also consult the Handbook on the Gospel of Mark for parallel or similar verses.