This study describes the propagation of direct and diffuse light through coral tissue and how changes in the directional quality of light affect photosynthesis. Scalar irradiance microsensors were used in vivo to measure tissue light propagation of incident collimated and diffuse irradiance. O2 microsensors were used to estimate changes in local O2 evolution. The results show that the directional quality of incident irradiance affects both coral optics and photosynthesis. Collimated irradiance is enhanced at the coral surface while diffuse irradiance is enhanced at the coral skeleton. Coral O2 evolution is enhanced under collimated compared to diffuse light. It is concluded that the directional quality of light is an important and hitherto ignored parameter in coral photosynthesis.