Dell monitors are not validated in a dark room. All monitors are inspected per industry standard, which is with 150lux ambient lighting (similar to typical office lighting).
Based on that picture, it is not defective and passes our manufacturer specification for overall uniformity. We could not issue an exchange. If purchased directly from Dell, you may return it for refund inside the first 30 days from the invoice date. If purchased from a reseller, check their return policy.
So what about when i have to work at night? It will be very distracted. I check with the reseller they said i now have to contract with dell customer service. They cant do anything about this one!
The only thing you can do is keep the lights on in the room. Dell cannot exchange this. You stated, "I just brought my monitor". I find it hard to believe that the reseller does not have at least a 15 day return policy. Contact them again and demand to return it to them for refund. Then buy a monitor directly from Dell to get the full warranty.