Which condition will decrease the life of a black light bulb?

Line voltage fluctuations can decrease the life of a black light bulb because these variations can cause the bulb to experience rapid changes in energy consumption. When the voltage is higher than the rated voltage, it can lead to overheating, which may cause damage to the filament or the internal components of the bulb. Conversely, if the voltage drops significantly, the bulb may not operate correctly, potentially leading to erratic behavior that can stress the components. Both scenarios create an unstable operating environment that can significantly shorten the bulb's lifespan compared to steady, consistent voltage levels.

Excessive use of the bulb generally does wear it out over time, but it is more about the overall hours of use rather than an immediate cause of premature failure. Low temperatures typically do not affect the functioning of light bulbs to the extent that they reduce their life; they may slightly affect luminosity, but not lifespan significantly. High humidity can also lead to issues, such as potential corrosion or failure of electrical contacts, but it is not as immediate in its effect on lifespan compared to voltage fluctuations that directly impact the bulb's operational stability.