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In this work carrier lifetime investigations by applying photoluminescence frequency domain technique to investigate blue and green light emitting diode (LED) structures, thus representing wide spectra for the InGaN LEDs were performed. Similar measurements have been carried out in GaN at extremely low excited carrier densities [1], as low as 1 mW/cm2 by using UV LED as an excitation source. For these measurements we applied laser diode (LD), to excite resonantly the MQW's in the sample investigated with modulated light. This allowed us to cover a broad range of excitation power density (1 – 500 mW/cm2). To analyze the activation mechanisms measurements down to 10 K temperatures were performed. The non-equilibrium charge carrier lifetime dynamics was investigated by applying a model with a superposition of exponential and stretch exponential decay depended on the sample and on the measurement condition. The uniqueness of this method is the possibility to study the transient processes in structures under very low to low non-equilibrium charge carrier densities at an un-saturated recombination channel condition.