When exit lights and way point signs are going to be used (as in during a fire, or such), they should be down near a skirting board hieght.
You can't stand up in a smoke/heat-laden atmosphere for long.
The number of Fire deaths caused by this annually would prove this.
Considering that smoke will spread along the upper parts of a compartment in a building and move downwards towards the floor, would suggest to me that our thinking of Escape lighting is backwards.
Just my opinion though.
Let's face it, these days if you're not young, you're old - Red Green