I think it is there to help you see down there at night. or it would be a mood light?

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07 Tundra DC 4x4, Radiant Red, debadged, Bed Mat, Brushed stainless steel step boards, Auto Dimming Rear View Mirror, Heated Towing Mirrors, 18” Alloy Wheels, Cold Kit, Mud Flaps, Tow Package, Rear Sliding Window, All Weather Floor Mats, TomTom 920T