A room-temperature photocurrent measurement technique is used to determine the effective nitrogen concentration in the active region of GaAs1−xPxN (LED’s) designed for green (x=1), yellow (x=0.85) and orange (x=0.65) light emission. A theoretical expression of the photocurrent signal is presented, which is in good agreement with the experimentally observed behavior of the investigated diodes. The investigation of different vapor phase epitaxy-GaAs1−xPxN LED’s reveals that the external quantum efficiency mainly depends on the product of effective nitrogen concentration and minority-carrier lifetime.