Dana Riddle has shown that photosynthesis shuts down in species of corals such as Porities, found in shallow tidal pools, when par levels reach a certain intensity during the day as the sun is on it way to approching it highest point in the sky.
He refers to this as Photo-inhibition as opposed to Photo-saturation which is the level of light intensity where the rate of photosynthesis has reached it's peak.
Figure 3. …the method described in the text defines the onset of Photosynthetic Saturation.
In this hypothetical situation, the Saturation begins at a light intensity of ~400 µmol·m˛·sec
(or about 20,000 lux). Using a similar method, onset of Photoinhibition would be about 700 µmol·m˛·sec (or about 35,000 lux).