The photo-dimerization characteristics of coumarin pendants within amphiphilic random copolymer micelles in aqueous solution was comprehensively investigated using various selected wavelength light in the UV-Vis-NIR region. The time-dependent photo-dimerization degree (PD) changes in the photo-dimerization experiments showed saturating behaviors with intensity-independent of PD max values at 28%, 44%, 92%, 85%, 36%, 35%, 32% and 31% for 254, 288, 320, 360, 400, 500, 650 and 900 nm irradiations, respectively. The irradiation experiments at 254 and 288 nm announced the occurring of an asymmetric equilibrium of photo-dimerization and photo-cleavage at the used conditions. Both the alternative irradiation cycles of 360 and 254 nm, 650 and 254 nm showed a partially, but evidently reversible photo-dimerization tendency.