There are some possible reasons:
What Can Cause Early Failure or Reduced Life Expectancy of Deuterium Lamps?
Lamp ignition frequency
The number of deuterium lamp ignitions is inversely proportional to its useful output life. A practice of leaving the lamp on continuously will tend to decrease its useful life by about 3-fold, based on an eight-hour workday. However, turning the lamp on and off during the day for breaks, etc., will probably shorten lamp lifetime and will be less productive as the lamp needs to warm up for 30 minutes to stabilize.
Contamination of the outer envelope:
Do not touch the lamp with bare fingers. The oils, etc. from your skin will burn onto the quartz envelope, and produce a discoloration, which may reduce light emission or possibly lead to a stress failure. If you do touch the lamp surface inadvertently, swab the glass with isopropyl alcohol (2-propanol) to remove the contaminants before installing the lamp.
Physical shock
A physical shock to the instrument or detector module, when the lamp is hot, can damage or break the lamp filament. (At approximately 2700 degrees Kelvin, the filament is almost liquid when the lamp is on!)
Very Important: Always allow the lamp to cool down before turning it back on. Powering on a hot lamp may negatively impact the structural integrity of the filament.
