Clean white light. 3,100? K color temperature, excellent 92.6 CRI, 37,913 initial lumens. The 3,100? K has a very high 1.82 PPF 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 PPF 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.