Those with two are lighter, but generally provide a beam with less brightness. Ni-cads are the most economical and environmentally sensible, since they can be recharged, and disposal of battery lead is not an issue. But they have the shortest charge and you must buy a re-charging unit. Alkaline batteries last longer per charge, but you get one use. Lithium batteries feature a long life, and excel in extreme cold, but are expensive.
Bulbs come in a variety of shapes, sizes, light intensities, power-draining properties and prices.
Krypton and halogen bulbs provide more intense beams than standard bulbs, but also drain more power from the batteries. Activities such as mountaineering or diving require an intense beam. But for the average user, perhaps the most important considerations are availability and price. Some lights feature as an option a rubber tab for that purpose. Lanyards , standard on some models, come in handy for hanging from a tree or from the light loops on the ceiling of a tent.