Headlight is the most comfortable and easy to use among all types of illumination options (flashlights, mostly). It's used in various types of activities including climbing, biking, hiking, camping, etc.
All modern headlamps use LED lighting (Light Emitting Diodes), but in rare cases there are halogen based headlamps. Halogens have high lumen output and range, but they are heavy and not as durable as LEDs. Light Emitting Diodes are 4 times ligher, smaller and much more durable. Also, LEDs consume less energy than halogens.
Light distribution mostly depends on the type of the beam. Some headlamps have either flood or spot light, some have both modes and some have smooth transition between these two types.
A flood light is useful for short distances. It offers a wide-angle light distribution that is best for general purpose when camping, reading, etc.
A spot light is best for longer distances. Light is emitted at a narrower angle to light farther. Useful for mountain biking, trail running, backcountry skiing, etc. For the best experience, it is recommended that your flashlight had both flood and spot light modes.
A - Flood Light
B - Spot Light
The total quantity of visible light emitted by a source (headlamp) is measured in Lumens.
Higher the number, the brighter the headlamp. Keep in mind that higher lumens donesn't necessarily mean that it can light farther. It depends on many other things such as beam type, light type, etc. For example, 200 lm spot beam headlamp might light farther than 350 lm flood light headlamp.
Regulated and Unregulated
Headlamp run time is called the time it takes to reduce the original power of a headlamp to 10%. Obviously, the headlamp that stays bright for a longer period of time is better. For that reason, there are headlamps with regulated output. It stays brighter for a longer time but dies quickly in the end.
You should definitely buy a headlamps with regulated output rather than unregulated one.
Size and Weight
Longer run time and brighter light in most cases means larger size and weight. This is mostly because the number of batteries. Some headlamps have battery packs mounted on the back side of the belt.
Most headlamps are very light. The heavy ones are ones that operate with external battery packs. So you may skip this part and read more about other details.
Cheap headlamps are not waterproof in most cases. This is a big problem when using in rain. For the best experience, choose waterproof hedlamps.
Most waterproof headlamps are rated from IPX4 to IPX7. In short, IPX4 headlamps are splashproof/ranproof and IPX7 rated headlamps can withstand being submerged in water.
Related: All About Waterproofing.
Photo by Josh Mathe
There are some more details you should play attention to. Here is a short list of some features you should know about before you buy a headlamp:
It is best at night when moving around campsite. Also red light does not constrict your pupils so you can see better at night.
Stroboscope / Blinking Light
Blinking light is used for many purposes. Being noticed when lost, getting attention on the road, etc. Also it can turn your campsite into a night club.
The ability to tilt the angle of the headlamp is very useful in many situation. Especially when you don't want to make your friends blind while moving around campsite.
You should consider the alignment and type of headlight buttons and switches. Keep in mind that you'll have to operate this buttons with your gloves.
Lock mode protects all buttons from being pressed accidentally. Useful for storage or transit. Finding out your flashlight dead because it was turned on during several hours in your backpack is not the thing you wish to happen.
Best for energy saving.
The light sensor automatically adjusts brightness and beam pattern, optimizing battery use.