EVEN THOUGH THE RPTED VISIBILITY WAS 7 MI; THE FLC OF A B777 COULD NOT SEE MORE THAN 1 PT 5 MI AT MOST DURING A VISUAL APCH WITH SIDE-STEP TO PARALLEL RWYS CAUSING THEM TO NOT SEE ANOTHER ACFT ON FINAL AHEAD UNTIL THEY WERE WITHIN 500 FT OF THE OTHER ACFT.

Narrative

ATIS STATED VISIBILITY OF 7 MI; APCHS WERE RWY 25L ILS AND RWY 24R ILS AND VISUALS TO ALL OTHER RWYS. THE VERT VISIBILITY FROM THE ACFT APPEARED TO BE 3/4 MI. THE HORIZ VISIBILITY ON THE RWY 25L ILS APCH WAS 1 1/2 MI (AT BEST). THE SUN WAS SETTING AND CAUSING REDUCED VISIBILITY OUTSIDE AND INSIDE THE COCKPIT SINCE THE SUN WAS ALMOST DIRECTLY IN OUR EYES. OUTSIDE AND INSIDE THE RWY 25L (OM) WE WERE DIRECTED TO 'SIDESTEP RWY 25R.' WE HAD TOLD ATC WE COULD NOT SEE THE RWY 25R. WE CONTINUED FLYING THE RWY 25L ILS UNTIL THE TFC IN FRONT OF US; ALSO LNDG RWY 25L (AT 300 FT VERT/500 FT HORIZ); WAS OBSERVED. EVASIVE ACTION WAS TAKEN TO THE N OF RWY 25L (LOC). RWY 25R THEN BECAME VISIBLE AT APPROX 1 1/2 MI FINAL AND 400-500 FT VERTLY. LNDG WAS UNEVENTFUL. ATC DIRECTIVES WERE BASED UPON 'THEIR' 7 MI VISIBILITY. THE ACTUAL VISUAL/ACFT VISIBILITY WAS 1 1/2 MI (MAX). ZLA IS CLRING/MANDATING PLTS FLY A VISUAL APCH TO A RWY THEY CANNOT SEE (TO INCREASE TFC FLOW) RESULTING IN THE ILS RWY 25L APCH BEING FLOWN TO WHERE RWY 25R CAN BE SEEN -- AT WHICH POINT THE RWY 25L TFC CONFLICT APPEARED. VISUALS IN LAX SHOULD BE BASED UPON THE PLT'S OBSERVED VISIBILITIES; WHICH IN THIS CASE WERE 3 TIMES LESS THAN RPTED BY ATC. WE WERE PLACED IN A POS WHERE WE WERE NOT TO CONTINUE THE RWY 25L ILS AND COULD NOT SEE RWY 25R FOR THE VISUAL AND NOT GAR DUE TO TFC.