The total efficiency is generally uncertain, while fraction of time per night is extremely uncertain in many cases. The CTIO fiber IFU is an estimate from Tom Ingerson.
Power is dimensionless since it is normalized to the fiducial.
The scale for power is proportional to the product of collecting area, weather, efficiency and available fraction of telescope time, divided by the square of the seeing. In the case of ranges, I used the upper end of the fraction range, but somewhere near the middle of the image quality range.