It doesnt need to be that bright to see the actual image itself though, without the back cover on you can just hold them up to a normal strip light and you can see fine.
I actually already tried in the past for different reasons: a portable halogen lamp at 20 centimeters keeps everything pitch black. By bringing the lamp closer you can light no more than a small circle with the actual pixels visible. You need a lot of lumen to see through a standard LCD panel.