You can buy cheap emergency lights at lowes for $30. I keep one at a friends's bussiness. Rather then gehave to get a reinspection on a fire inspection if one of the emergency lights fails, they just substitute this one. BTW, our local fire marshal's rule on emergency lights is to pretend you are a 80 yo elderly lady with a walker who has lost her driver's liscense due to vision, and has ever been to this bussiness before- Can you still see to get out? I know he drives the A/E firms nuts, but it makes more sense than some arbitary footcandle level.
I think these are of limited value in a residence. People know how to get arround their own house in the dark, where the exits are, etc. Most people carry cellphones that will provide a minimum level of illumination. I almost always have my surefire E2D with me. However, I have one of these in my shop, just because stuff get moved arround (both stuff being worked on, and things like stands, sawhorses, welders, and my horizontal bandsaw.), and a fall could be much more dangerious then in a house.