What statement about black light bulbs of the mercury arc type is false?

The assertion that variations in line voltage above 120 V will have little or no effect on the bulb is incorrect. Mercury arc black light bulbs are sensitive to the voltage supplied to them, and fluctuations in line voltage can significantly affect their performance. High variations in voltage can lead to poor functioning, reduced lifespan, inconsistent brightness, or even damage to the bulb. Thus, maintaining stable and appropriate voltage levels is crucial for ensuring optimal functionality of these bulbs.

The other statements correctly describe characteristics of mercury arc black light bulbs. They indeed perform better with high voltage; they are designed to emit UV light and may not be effective in environments too exposed to other forms of light; and they require time to warm up before reaching their maximum intensity output. Each of these elements contributes to the understanding of how these types of bulbs operate within their specific applications.