Lucalux PSL HPSSimple light or lumen maintenance is not enough to create plant growth. Plants require a certain radiation level to help with photosynthesis. The Lucalox PhotoSynthesis Light Lamp has been specially developed to provide stable lumen maintenance and increases Photosynthetically Active Radiation (PAR). Measured in micromole sec, the increased PAR output of the Lucalox PSL lamp best simulates natural daylight to maintain plant growth under artificial