Night Light by Source (image) University of Southern California Share Print E-Mail Caption The Lights Proximity Index (LPI) distinguishes three sources of light: urban areas (white light), fishing boats (green light), and oil/gas flares (red light). Credit Christoph Albrecht et al. in Geocarto International Usage Restrictions None Share Print E-Mail 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.