Update 08-02-13
While the idea of having emergency lighting in your shop is as important as ever, I no longer recommend the Sylvania lights described in this article. They worked well for about two years, but eventually, the internal rechargeable batteries died. The lights are designed so that there is no way to open them up to replace the battery.

Not being easily deterred, I openend one up by cutting grooves with the lathe so that I could remove the two ends. OK, that done, the battery is soldered in place. I removed it, but after considerable Google searching did not find a suitable replacement battery at a price that would make it worth the effort to repair the lights. That's too bad, because they are otherwise pretty handy to have around. I found that they got very low ratings by buyers on Amazon for the same reason.

So far, I haven't found a substitute light that I like. I eventually did find some replacement batteries at reasonable cost, so I'll continue to use these lights, but I can't recommend them.
End of update

Emergency Lighting

I've made it a rule in my shop to have automatic power-fail lighting near each of the work areas. One night quite a few years ago, I was sawing through a board on my radial arm saw when the power to our home went out. Suddenly, I found myself in total darkness with the saw still whining to a stop in the dark. That's an experience I'd rather not repeat with any of my machine tools. 

Since that time, I've used some inexpensive Sylvania emergency lights that plug directly into an outlet. They're left plugged into the outlet all the time, so the battery is always fully charged when it's needed. A single white LED illuminates as a night light when the room is dark and the power is on.  In the photo below I'm using my thumb to cover the photocell to simulate darkness.

el01.jpg (30171 bytes) Standby          el02.jpg (28828 bytes) Night-Light           el03.jpg (28153 bytes) Emergency Light

If the power goes off, a flashlight beam powered by 3 bright white LEDs illuminates and will provide light for an hour or more before the battery runs down. During a power outage - or any time you need it - the light can be unplugged and used as a handy flashlight; the power plug folds out of the way. They're not real bright, but provide enough light to see what you're doing in an emergency, and, unlike an ordinary flashlight, you don't have to grope around in the dark to find 'em. My only gripe is that the light covers up two outlets rather than just one, but that's a small price to pay for the safety and convenience that it provides.