Gro-Lux High Pressure Sodium 600W grow lamp are used as complete or additional artificial lighting of plants. Patented arc tube delivers the highest photosynthetic efficiecy. Performance maintained at an exceptional level due to improved structure of the outer bulb, - Optimised for the highest Phytolumens or PAR output. Industry leading lumen maintenance of 95% at the end of life. Recommended for use in greenhouses and indoor lighting.