Headlamp experts suggest that nearly everyone would benefit from keeping a tiny, compact headlamp on hand for emergencies. One-ounce headlamps fit into a glove compartment or emergency kit, or as a backup for a primary headlamp. However, they aren't generally bright enough for everyday use, and battery life can be short.
The emergency backup headlamp most often recommended in reviews is the Petzl e+LITE (*Est. $30), which is as small as a fifty-cent piece, weighs only an ounce and packs into a protective case. Unlike most Petzl headlamps, the e+LITE carries a ten-year warranty (most other Petzl models have a three-year warranty) and is waterproof to a depth of one meter. This headlamp includes a red LED for night vision, a strobe function and certification for use in hazardous (explosive) conditions.
You can use this headlamp on a clip as well as its elastic headband. The beam is wide to illuminate tasks very well, but can project usable light as far as 60 feet. Maximum output is 21 lumens (or 23 lux at two meters), so it's not as bright as some headlamps. But its main drawback is relatively short battery life - 35 hours at its high setting, 45 on low. This is plenty of time to get through most emergencies, however, and the CR2032 lithium-ion batteries can hold their charge for up to ten years.
The 1-ounce Black Diamond Ion (*Est. $20) is less expensive but dimmer, lacks the option of red light for night vision and provides shorter battery life. It uses only a single white 0.5-watt LED, while the Petzl e+LITE uses three white plus one red. The Black Diamond Ion is only water-resistant, not waterproof, carries a shorter three-year warranty and has a very short battery life of only 15 hours.