Whats that single Headlight looking thing on the outside of buildings

Walking around almost all new commercial construction and you will notice a single headlight looking light on the outside of the building.
Whats that light for ? I often get asked when installing them.
what this light is used for is emergency lighting so that when the power goes out inside a building you can see where you are going when you are following the exit signs to get out.
For years only emergency lighting powered by back up batteries needed to be inside a structure except for certain buildings which had generators and where required to have outside lights working on fire Escapes etc.
But that all changed a decade or so back now all structures must have lights outside on buildings to light the exit path.
One of the main reason for this is to prevent panic as it has been found after catastrophic fires how peoples remains where found behind open exit doors stacked up all because they could not see what they where stepping out into.
While these lights are a good idea and are not very designer looking they do serve a very important purpose but unfortunately are often the target of vandals and of course if the emergency light system is not properly maintained they do not work either. You may also find these light heads being used in restrooms and elevators depending on local codes as well.