The photon cross-correlations of different light fields, namely coherent light, mixed coherent and chaotic light, and chaotic light, in a changing process of light feedback intensity are investigated theoretically and experimentally via an unbalanced fiber interferometer, and the above-mentioned light fields are distinguished. The second-order photon cross-correlations of the light fields are analyzed as functions of delay time and coherence time. The results show that the second-order photon cross-correlation g^(2x)(τ) of coherent light only has a minimum value of 0.5 at zero delay time. The g^(2x)(τ) of chaotic light has two maximum peaks of 1.25 at symmetric delay time. The g^(2x)(τ) of mixed coherent and chaotic light not only has a minimum value at zero delay time but also has two maximum peaks at symmetric delay time. Meanwhile, as the proportion of chaotic light increases, the peak values of g^(2x)(τ) at symmetry delay time rise from 1 to 1.25 and the g^(2x)(0) at zero delay time increases from 0.5 to 1, indicating that the mixed light is transiting from coherent light to chaotic light. The g^(2x)(τ) of coherent light is measured experimentally under no light feedback, and the corresponding coherent time obtained is 65 ns. When the feedback intensity is 2.5%, the g^(2x)(τ) of the chaotic laser is measured. The proportion of chaotic light is 75%, and the corresponding coherent time is 0.7 ns. When the feedback intensity is 18%, the g^(2x)(τ) of chaotic laser in coherence collapse regime is measured, and its coherent time is 0.8 ns. The experimental results are in good agreement with the theoretical ones. It indicates that this method can clearly distinguish light fields with different proportions of chaotic light and their corresponding coherent time and thereby provide a theoretical and experimental basis for further revealing and monitoring the quantum statistics of output light fields.