This is a posting of mine from a flashlights forum. I guess it's OK to copy and paste it since I wrote it, but it does duplicate what's at another forum. Here goes:
To Consider Before You Purchase a Headlamp.
Many people shopping for a headlamp ask: “What’s the best headlamp?” There’s no global answer to this question, because the headlamp that’s right for you, depends almost entirely on your intended use. Answer each of the questions below, and you’ll get a headlamp that meets your needs.
1. Beam angle: Do you need throw, flood, either, or both?
Throw: Are you moving quickly through dark spaces, like a kayaker or bicyclist? Are you on a search and rescue team, where your hands are full but you need to be seeing into the distance? Than you want a beam that throws a spot. Spot headlamps are a specialty need, since most enthusiasts want a headlamp to provide a floody beam or a mixed beam, preferring a handheld for throw.
Flood: Are you working with your hands? Setting up camp? Doing crawlspace, attic, or electrical work in dark places? Jogging at night, and don’t want the “bouncing ball” effect? Working in an emergency tech, in an ER room, or underneath your car? Reading in bed? Or any other activity that requires peripheral vision? Then you want a floody, wide, even beam of 60-120 degrees that gives you lots of peripheral vision, lit at the same level as the center of your vision. Many inexpensive lights are sold as “flood” that have narrow beams of 30 or 40 degrees. A narrow flood is usually a disadvantage, requiring you to swivel your neck a lot to illuminate a close-up view. But, depending on your task, a narrow flood can also be an advantage (for example, using the computer at night--narrow flood lights just the keyboard but not the screen).
Do you want either floor OR throw? There are lots of lights that will switch between beams, some better than others. Lights that are both spot and flood usually employ compromises, compared to purpose-built lights. On the other hand, there are high-end caver’s lights that do both tasks brilliantly.
Do you want both flood AND throw, simultaneously? Variously called “directional flood,” or “spot with spill,” it’s a compromise between flood and throw. Lots of models provide this function. Many put a hotspot in the center of a floody beam, but some place a hotspot at the top of a floody beam. Others just fade gradually from bright center to flood. A few actually throw an even (narrow) flood beam. They’re often preferred by people who walk trails at night. But don’t try to read with them...it’s a frustrating experience.
2. Battery type -- a majority of modern LED headlamps run on either AAA, AA, or CR123. (There are specialty cell sizes, too.) CR123 have the energy/size advantage, are getting easier to find in U.S. stores, and are pricier. If you weight performance over accessibility, then consider CR123s. If you’re traveling to out-of-the-way places, and not carrying cells with you, you may want to stick to AAA and AA. Many enthusiasts seek 1xAA and 2xAA lights (which require more expensive circuitry to boost the voltage necessary to light the LED) because of the ubiquity and power of AA cells. Others prefer AAA cells because of smaller size (although 3 are often called for) and the less expensive headlamps that can be built around them.
3. Battery placement -- do you want a small, minimalist headlamp that feels like you’re just wearing a hat? Want to be able to lie down while using the headlamp? Then you want an up-front battery placement, perhaps a 1xAA, 2xAA, 3xAAA, or 1xCR123. Do you want powerful light and long runtimes? Wearing a helmet? Not lying down? Don’t mind the weight on your head? Then you should consider back-of-the-head battery placement, or a belt-mounted battery pack with a connecting cable. Be aware that cables are the source of failures and frustration, however.
4. Beam tint & artifacts -- more and more enthusiasts are turning to neutral and warm tints in LEDs as top manufacturers make them available. They excel in the out-of-doors, where they allow the user to better distinguish shades of brown and green, and also for workers who must distinguish colors (of electrical wires, for example). Enthusiasts tend to shun green and purple tints. Blue tints (cool-tint) are readily available and are preferred by some for their brilliance. Beams with no discernible tint are highly sought after. Recently coming to the market, high-CRI lights (which may come in a variety of tints) attempt to more closely mimic the full spectrum of color that incans are blessed with, and do a better job on illuminating browns, oranges, and reds, since red emissions are weak for traditional white LEDs. Tint is very much an area of personal preference, as well as task (does tint really matter when you’re using the light to read a book?) but once you determine your tint preference, you may find tint preference becomes more important than a light’s brightness. It’s common to see enthusiasts giving up lumens for a preferred tint.
Specialty red and green LEDs are available for people (such as astronomers, soldiers, sailors, and hunters) who are trying to retain night vision. Some manufacturers build a red LED into multi-beam lights for an all-in-one solution.
Many enthusiasts are intolerant of beam artifacts of any sort. Most manufacturers have figured out how to eliminate them. Mild artifacts are of little consequence if you’re hiking at night, but can be quite annoying if you’re trying to read. Artifacts become worse at closer distances.
5. Brightness required (often discussed as lumens) depends on usage. Newbies think that brighter is always better, and sometimes, that’s true. Bicyclists, joggers, search-and-rescue, and cavers generally can’t get enough light, and crave multi-hundred (or even thousand) lumen headlamps. Don’t chase small percentage increases in brightness, however. A 20% increase in intensity may be barely noticeable, if you’re concentrating on seeing a difference, but it takes around 100% increase before a beam looks significantly brighter, and intensity must be 300%-400% to look twice as bright. And yes, a light can be too bright. If you are working in a crawlspace or attic, you may find anything above 50 lumens is too bright. If you’re reading in the dark, 10 lumens can be too bright. If you’re on a sailboat at night, observing stars, checking on your sleeping kids, or otherwise trying to preserve your night vision, you may find even 1 lumen too bright. So make sure your light goes as low as you need it, not just as high as you need it.