Penlight

  A penlight is a small, pen-sized flashlight, usually containing two AA batteries or AAA batteries.

Additional recommended knowledge

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A number of different designs are common. In some an incandescent light bulb has an integral lens that focuses the light, thus no reflector is built into the penlight. Others, such as the well known Maglite brand use incandescent bulbs and standard reflectors, while LED bulbs are becoming increasingly common.

"Penlight" is also a colloquial term for a standard AA-type battery.