Here's what Laser Products, the makers of Sure-Fire Tactical lights, has to say about it.
The lumen is a measure of the amount of light, as opposed to the intensity of light. A typical 75 watt incandescent light bulb has an output of 1080 lumens. At a distance of ten feet, this light bulb would provide uniform illumination of slighty less than one lumen per square foot.
Another measure of light is the Candlepower, which is not a measure of the amount of light but a measure of the intensity at a given point in a foucsed beam. Because such a measure produces impressively large numbers, it is often quoted by other manufacturers. For example, the above 75 watt bulb equipped with a reflector could be rated, under certain conditions, as producing over 2 million candlepower. Since this rating is highly dependent uopn which point within a given beam is being measured, candlepower ratings can be very unrealistic and, therefore, certainly not a true measure of the amount of light being produced.
Get all that? [;)]