Context and question: Luminous efficacy of a light source may be defined in two ways. The radiant luminous efficacy (LER) is the ratio of the visible light flux emitted (the luminous flux) to the total power radiated over all wavelengths. The source luminous efficacy (LES) is the ratio of the visible light flux emitted (the luminous flux) to the total power input to the source, such as a lamp. Visible light is measured in lumens, a unit which is defined in part by the differing sensitivity of the human eye to different wavelengths of light. Not all wavelengths of visible electromagnetic energy are equally effective at stimulating the human eye; the luminous efficacy of radiant energy (LER) is a measure of how well the distribution of energy matches the perception of the eye. The units of luminous efficacy are "lumens per watt" (lpw). The maximum LER possible is 683 lm/W for monochromatic green light at 555 nanometers wavelength, the peak sensitivity of the human eye.
What is the minimum LER possible?
Answer: unanswerable
Context and question: The city's elevation is 2,643 ft (806 m) above sea level (as measured at the Tucson International Airport). Tucson is situated on an alluvial plain in the Sonoran desert, surrounded by five minor ranges of mountains: the Santa Catalina Mountains and the Tortolita Mountains to the north, the Santa Rita Mountains to the south, the Rincon Mountains to the east, and the Tucson Mountains to the west. The high point of the Santa Catalina Mountains is 9,157 ft (2,791 m) Mount Lemmon, the southernmost ski destination in the continental U.S., while the Tucson Mountains include 4,687 ft (1,429 m) Wasson Peak. The highest point in the area is Mount Wrightson, found in the Santa Rita Mountains at 9,453 ft (2,881 m) above sea level.
What mountain range is west of Tucson?
Answer: Tucson Mountains
Context and question: In addition to limiting the total average power used by the device, the USB specification limits the inrush current (i.e., that used to charge decoupling and filter capacitors) when the device is first connected. Otherwise, connecting a device could cause problems with the host's internal power. USB devices are also required to automatically enter ultra low-power suspend mode when the USB host is suspended. Nevertheless, many USB host interfaces do not cut off the power supply to USB devices when they are suspended.
Many USB host interfaces do not what?
Answer:
cut off the power supply to USB devices when they are suspended