315w CDM 942 4200k grow bulb Superior colour quality. Crisp white light. 4200k colour temperature. High 92CRI. 34,300 initial lumen’s (109lm/w). High 90% lumen maintenance at 8,000hr. High 85% PPF maintenance at 20,000hr. Unique Open Rated Lamp construction reduces radiant heat from the arc tube and is suitable for open fixture use. Until the lamp has achieved a least 10 hours of operation, the lamp should never be turned off longer than 2 minutes, including the installation test. In case this happens, you will have to wait 1 hour before switching on again. Not doing so may lead to ignition problems.