The human eye contains a certain protein called rhodopsin that changes shape when it is exposed to light. When rhodopsin absorbs light, part of it undergoes a chemical change. This is how eyes sense the presence of light.
The human eye contains a molecule called 11-cis-retinal that changes conformation when struck with light of sufficient energy. The change in conformation triggers a series of events that results in an electrical signal being sent to the brain. The minimum energy required to change the conformation of 11-cis-retinal within the eye is about 164 {\rm kJ}/{\rm mol}.
