Penetration of Light Into the Uterus of Pregnant Mammals

The fraction of incident light which reaches the uterine lumen in pregnant rats and guinea‐pigs was studied with a surgically implanted optical fiber. Penetration of visible spectrum light (400–650‐nm wavelengths) into the uterus was examined. The effects of clipping the hair, retracting the skin, and retracting the abdominal wall on the penetration of light was also assessed to determine the relative amount of light transmitted through each layer between the external environment and the uterus. The presence of significant transmission at biologically relevant wavelengths raises the possibility that environmental lighting may reach the fetus and influence development