In this study, human colon cancer cell lines also expressed Opn3 and, from the fact that blue LED's effect was inhibited by Opn3 knockdown or inhibiting the Gi/o G‐protein α‐subunit, Opn3 may play an important role as a G protein‐coupled photoreceptor by cAMP signaling in inducing autophagy. Here, OPN3 is linked to malignant colon neoplasm.