Context: During ordinary operation, the tungsten of the filament evaporates; hotter, more-efficient filaments evaporate faster. Because of this, the lifetime of a filament lamp is a trade-off between efficiency and longevity. The trade-off is typically set to provide a lifetime of several hundred to 2,000 hours for lamps used for general illumination. Theatrical, photographic, and projection lamps may have a useful life of only a few hours, trading life expectancy for high output in a compact form. Long-life general service lamps have lower efficiency but are used where the cost of changing the lamp is high compared to the value of energy used.

Question: What determines how fast a tungsten filament evaporates?
Answer: hotter, more-efficient filaments evaporate faster

Question: What is the typical goal for the life of a tungsten filament bulb?
Answer: several hundred to 2,000 hours

Question: Which types of lamps may have particularly short lives?
Answer: Theatrical, photographic, and projection lamps

Question: What is the typical tradeoff in light bulb design?
Answer: efficiency and longevity

Question: What does not determine how fast a tungsten filament evaporates?
Answer: Unanswerable

Question: What is not a trade-off between efficiency and longevity?
Answer: Unanswerable

Question: What type of bulb typically has a life of 3000 hours?
Answer: Unanswerable

Question: What type of lamp has higher efficiency but are used where the cost is high compared to the value of energy used?
Answer: Unanswerable

Question: What type of lamp has a useful life of a few days?
Answer: Unanswerable