Context: Lamps designed for different voltages have different luminous efficacy. For example, a 100-watt, 120-volt lamp will produce about 17.1 lumens per watt. A lamp with the same rated lifetime but designed for 230 V would produce only around 12.8 lumens per watt, and a similar lamp designed for 30 volts (train lighting) would produce as much as 19.8 lumens per watt. Lower voltage lamps have a thicker filament, for the same power rating. They can run hotter for the same lifetime before the filament evaporates.

Question: How many lumens per watt does a typical 100-watt, 120-volt lamp produce?
Answer: 17.1 lumens per watt

Question: How does filament size relate to voltage level?
Answer: Lower voltage lamps have a thicker filament

Question: What is the effect of a thicker filament on bulb temperature?
Answer: They can run hotter for the same lifetime before the filament evaporates.

Question: How many lumens per watt does a typical train light produce?
Answer: as much as 19.8 lumens per watt

Question: What watt lamp can produce 17.3 lumens per watt?
Answer: Unanswerable

Question: How does a filament size not relate to voltage level?
Answer: Unanswerable

Question: What is not effect of a thicker filament on bulb temperature?
Answer: Unanswerable

Question: How many lumens per watt does an atypical train light produce?
Answer: Unanswerable