The 3,100°K has a very high 1.82 PPFD per second light source. 4,200°K color temperature, excellent 97.5 CRI, 31,127 initial lumens. The 4,200°K has very high 1.70 PPFD per second light source. Good lumen maintenance and excellent PPF performance throughout lamp life. Unique open-rated lamp construction, including a ceramic arc tube contained in a protective quartz glass shroud with PGZX18 base, reduces radiant heat from the arc tube and makes these lamps suitable for open rated fixture use.