Clean white light. 3,100?K color temperature, excellent, 92.6 CRI, 38,698 lumens at the 100 hour test (122Lm/W). The 3,100?K has very high 1.856 PPFD per second light source. 4,200?K color temperature, excellent 92.8 CRI, 34,625 lumens at the 100 hour test (110Lm/W). The 4,200?K has very high 1.778 PPFD per second light source. Good lumen maintenance and continued excellent PPF performance throughout lamp life. Unique open rated lamp construction reduces radiant heat from the arc tube and is suitable for open fixture use with a PGZX18 base.