Okay. I dug out one of my shake lights. It doesn't have a brand name on it, and I've long since discarded the packaging. I bought it at a surplus store (on Morse Road near Cleveland Ave in Columbus, if you'r interested) and it came with a keyring LED that has a carabiner-style spring clip.

Patent No. 5,347,186 is stamped on it, but that number refers simply to a Liner Motion Electric Power Generator so I can't give you a manufacturer name.

This light runs EITHER on batteries or on shake charge. If I shake it up good, the shake light lasts for a few minutes, and a few seconds of shaking thereafter keeps it going.

It contains two wafer batteries, and I have no idea how long they'll last.

The switch is a push-button three-state. On (with batteries), On (with shake) and Off.

The bulb is a single LED with a magnifying lens.

All-in-all, it provides me with enough light at night using the shake mode, and the battery mode is more than sufficient to read by - at least until the batteries poop out.

I have seen "shake only" lights that don't seem to work very well. So the real answer is that some shake lights are a joke and some are not. Buyer Beware.