We report an infrared comparative photoluminescence and absorption study of optical properties in quaternary GaInAsSb/AlGaAsSb strained single‐quantum‐well structures grown by molecular beam epitaxy with the indium composition of 0.25 and 0.33. The light‐hole‐related luminescence structure observed in the lower indium composition sample disappears in the sample with higher indium composition due to the larger band splitting of heavy and light holes induced by the strain. This observed transition from type I to type II states for light holes is in good agreement with our theoretical prediction that it may occur for the indium composition larger than 0.30. ©1996 American Institute of Physics.