There are certain areas on the Refinery map where I find the lighting gets dark quite fast, though gradually, for no apparent reason. I've taken screenshots when it happened from the positions I was standing in. After a short while, the problem goes away however.

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PC Specs:

CPU: i7 4790K
GPU: GTX970
RAM: 32GB DDR3 @1866mhz
HDD: Samsung 840 SSD