CaMPARI, or Calcium Modulated Photoactivatable Ratiometric Integrator is a photoconvertible protein construct, enables imaging of integrated calcium activity of large populations of cells over a defined time window. Calcium indicators have found extensive use for imaging and measuring changes in Ca2+ levels associated with neural activity. 
 
CaMPARI is based on EosFP, a fluorescent protein whose emission changes from green to red upon irradiation with UV-light (~400 nm). By engineering libraries of EosFP variants, researchers were able to develop a protein that undergoes significantly faster green-to-red photoconversion (PC) only when calcium is present while PC light is applied. This permanent conversion provides the ability to record calcium activity for all areas illuminated by PC-light. The red fluorescence intensity correlates with calcium activity.