A B1900 TAXIING FOR TKOF IS CONFUSED DURING TAXI AS TO WHICH PATH TO FOLLOW TO GET TO THE TKOF END OF THE RWY. FEW TXWY LIGHTS AT TXWY K WITH RAIN CAUSED THE CONFUSION. ACFT ENTERS ACTIVE RWY WITHOUT CLRNC AT PHL.

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FLT FROM PHL TO ACY. THE FLT WAS RUNNING LATE DUE TO THE POOR WX (HVY RAIN; WINDS AND POOR VISIBILITY AT NIGHT). WE EXCHANGED CREWS AND CALLED FOR TAXI. BOTH THE CAPT AND I WERE NEW TO THE AREA AND WERE VERY UNFAMILIAR WITH ARPT LAYOUT; ESPECIALLY TAXIING TO RWY 9L. AS WE PULLED OUT OF OUR PARKING AREA FOLLOWING THE ARPT DIAGRAM TO RWY 9L (THIS AREA IS VERY POORLY LIT WITH NO CTRLINE TAXI LIGHTS IN THIS SECTION); TXWY K MAKES A 'Y' AND WE PROCEEDED TO VEER TOWARDS THE R IN THE PROPER DIRECTION OF RWY 9L. HOWEVER; WE DIDN'T VEER SHARP ENOUGH AND ENDED UP TAXIING ONTO RWY 9L. WE IMMEDIATELY RECOGNIZED OUR ERROR AND WERE ABLE TO TAKE THE IMMEDIATE EXIT ON TXWY L. WE WERE MERELY ON THE RWY FOR SPLIT SECONDS; WITH NO OTHER AIRPLANES IN OR OUTBOUND ON THAT RWY AT THAT TIME. GND CTL DIDN'T EVEN NOTICE WE HAD DEVIATED. REMAINDER OF THE TAXI/FLT WAS UNEVENTFUL. CONTRIBUTING FACTORS: 1) UNFAMILIARITY WITH ARPT. 2) POORLY LIT AND MARKED AREA. 3) WX -- POOLS OF WATER STANDING ON TXWY; REFLECTING OVERHEAD LIGHTING MAKING IT DIFFICULT IF NOT ALMOST IMPOSSIBLE (WITH WIND EFFECTS ON STANDING WATER) TO CLRLY IDENT TXWY/RWY CTRLINE/MARKINGS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR WAS FLYING AS FO. TAXIING FROM TXWY E; THEIR INSTRUCTIONS WERE TO TURN R ON TXWY K TO RWY 9L. DURING THE TURN ONTO TXWY K; THERE IS A 'Y' INTXN OF TXWY K AND TXWY K2. THE AREA BY TXWY K2 IS POORLY LIT. FURTHER CONFUSION WAS CAUSED BY STANDING WATER ON THE TXWY. AS THE ACFT BEGAN ITS TURN TO THE R; IT STOPPED THE TURN EARLY; THE FLC TAXIED ONTO RWY 9L FOR A FEW SECONDS THEN IMMEDIATELY OFF THE RWY. THE TWR NEVER SAID ANYTHING ABOUT THE RWY INCURSION; PROBABLY BECAUSE OF REDUCED VISIBILITY. RPTR STATED THAT RWY AND TXWY LIGHTING WERE POOR ONLY WHERE THE INCURSION TOOK PLACE; ALL THE REST OF THE LIGHTING WAS PROPER.