Lights Proximity Index of Puerto Rico (image) University of Southern California Caption The lights proximity index (LPI) values surrounding Puerto Rico (left) and the undifferentiated night light from the island (right). Credit Christoph Albrecht et al. in Geocarto International Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.