Step #1

Create a gradiant or use the Black,White gradient provided in Photoshop. Resolution is not critical, you can match the final pictures dimensions and resoultion.

Step #2

Add Noise to create that gritty textural effect.

Step #3

Drop the gradient into a new layer in the final image.

Use the edit/transform/distort. to get the light into an approiate shape and perspective.

Step #4

Use the lighten apply method and lower the opacity to 20-30%. Finally use a 30% eraser brush to add streaks, holding down the shift key on each stroke to keep it straight.