It is not necessary in many cases, but in places like operating rooms and emergency rooms, power is absolutely required for lighting and running equipment. People would die if power went off.
UPS = Uninterruptible Power Supply
You can't "calculate" it...
Uninterruptible Power Supply
An (UPS) Uninterruptible power supply
Uninterruptible Power Supply
UPS (uninterruptible power supply)
uninterruptible power supply
As long as the UPS has power. UPS's have different run times.
UPS (uninterruptible power supply)
Uninterruptible supply
the ups was invented by the great american christopher latthem
Give you time to shut down if you lose your power. Not a replacement for regular back-ups though.