Whenever love, peace, joy, goodness and fruits that are sweet to the soul are absent, darkness can be found. Hatred, bitterness, cruelties, anger and a host of others emotions can usually be found where love, peace, joy and goodness doesn't exist. A heart that lacks love, peace, joy and goodness is a heart that needs to be touched by Jesus and filled with the Holy Spirit so that Godly fruit will come forth.
There is a scripture that states "the mouth speaks forth the abundance of the heart". How true and usually you can tell what a person's heart is filled with by the words that they speak and the things they express.
Whenever you encounter someone that is struggling and the word of their mouth exposes the darkness of their heart. Pray for them and sow words of love and encouragement into them. Remember, we fight not against flesh and blood, but against principalities, powers and spiritual wickedness in high places. Become a deliverer, by sowing seeds of love, peace and joy.
Let your light shine brightly.