Brighter isn't always better. A flashlight that's too bright can wake your sleeping partner, create so much glare that a page is hard to read or make it hard to adjust your vision back to the dark. The most flexible (and expensive) flashlights let you select from among several levels of light. Lower light levels (7 to 9 lumens) are better for closeup tasks and night walks, while higher levels let you see much further. Intermediate levels (about 45 lumens) are good for changing a tire or cooking a meal. As a rough comparison, the familiar MagLite 2D flashlight (*Est. $20) averages 36 lumens -- with a Xenon bulb that's brighter than a cheaper 2D flashlight. A flashlight that provides 80 lumens, comparable to a MagLite 3D (*Est. $22), is bright enough to temporarily blind someone close to you, and some flashlights provide even brighter strobe lights to summon rescuers.
Not all flashlight manufacturers specify the lumens, and measurement methods vary even among those that do. Furthermore, two flashlights that put out the same light in lumens may concentrate that light in totally different ways -- with one throwing a small spotlight beam a long distance and another spreading the light more for closeup or intermediate tasks. Also, the quality of the circle of light varies -- smoothly graduated or with dim spots, rings or other unevenness.
As if this weren't complicated enough, brightness varies over time -- not only gradually as batteries fade, but also within a few seconds of turning some flashlights on. Minimizing this dimming is one major reason some flashlights cost much more than others. It requires more than a top-quality LED -- it also needs digital technology, which adds to the price.