The light tunnel is a tiny rectangular hallway made of mirrors. The tunnel gets hot because it is close to the lamp. The glue holding the tunnel together becomes brittle and fragile. 
Light Tunnel Failure occurs when:
- The bulb fails with a pop
- The TV receives a sharp impact
- The tunnel falls apart for no apparent reason
One side of the hallway moves or collapses, blocking the light, causing a shadow effect on the image.  
The most common symptom of a defective light tunnel is:
Shadow on one side of the image
(Usually Left side)
Light
Tunnel Replacement requires removal and dis-assembly of the Optical
Engine. This is a complicated process and not recommended for in-experienced technicians.
Light Tunnel replacement is available for all Samsung models.