If you lose main power then use your computer 5 volt power supply to
light up LED flashlights.
You can buy over the counter a USB light that can light up your
but this is a longer term system in case you lose power. You do have
backup power for your computer, right?
They make a 27 LED hand held light for about $2.50. It uses 3 AAA
batteries which will produce 4.5 V when new.
If you reduce your computer 5 V supply, it can be wired to the battery
holder inside the light.
Probably best to remove the batteries first.
The voltage drop across a forward biased diode ( one that is
conducting) is about 0.6 V.
Add a low cost diode in series with the 5 V supply and you have the
right voltage to power the LED light.
Sometimes 5 volt cell phone chargers are available at a low cost.
It needs to be a better quality charger that has a regulated output to
avoid extra high voltage.