A Lancair Columbia pilot reported a failure of one of the main landing gear brakes during landing roll; resulting in a runway excursion and damage to the aircraft.

Narrative

Aircraft lost left brake actuation while under braking in the landing roll past the half-way point of the runway which prevented slowing the aircraft to a stop on the runway. The aircraft has a castering nose wheel and requires differential braking to control steering; so without equal braking only partial right brake could be used to slow the aircraft to prevent a more extreme turn to the right. Given the lack of braking control; the aircraft departed the runway at the departure end of the runway.During the runway overrun; the right wing impacted a runway end light resulting in visible damage to the composite skin on the underside of the right wing. The damage to the wing appears non-structural.To effect a complete stop; the right brake was applied fully to turn the aircraft to the right and skid to a stop once the nose wheel reached full deflection. If the aircraft had a steerable nose wheel; the right brake may have been able to stop the aircraft while maintaining directional control; but this is not possible in a castering nose wheel aircraft with a single sided brake failure.The left brake master cylinder and wheel assembly still need to be inspected to determine the cause of the failure. There was no binding or noise coming from the wheels or brakes when the aircraft was being towed back to the hangar.