Penlight
A penlight is a small flashlight in the shape of a pen. A penlight usually uses a small light known as an "LED" (Light Emitting Diode) but it can also use a small lightbulb made just for small flashlights.
The LED lights up when power is run through it. Making the penlight light up is as simple as pressing a button, or screwing the end on tighter so it makes contact with the batteries.
Most of the time, penlights use two or three AA, AAA, or AAAA batteries. AAAA are a newer, thinner type of battery, most commonly found in small electronics. It started with the AA size batteries.
Penlights can be made out of plastic or metal, and can be any color. They most often have a little clip, to hold it on your shirt or something.
Penlight Media
A set of LED flashlights. C8 style on the left (Sofirn C8T: up to 1,310 lm), tube style on the right (Sofirn SP31; up to 1,100 lm).
The angle-head flashlight (Fulton MX-991U) on the left uses an incandescent bulb, while the adjustable angle-head flashlight (Streamlight Sidewinder) on the right uses LEDs to give white, red, blue, and infrared light
Miniature incandescent bulbs for use in flashlights: The tungsten filament bulb was essential to turn the flashlight from a novelty to a useful tool.
Two LED flashlight extremes: Olight SR90, 2,200 lumens (left), Foursevens Mini MLR2, 180 lumens (middle), AA battery for size comparison (right)
Miniature LED flashlight on a key chain, powered by lithium primary coin batteries
Multiple 5 mm LEDs may be used in small flashlights.
A medical halogen penlight to observe pupillary light reflex
An LED headlamp made by energizer. Runs on AAA batteries.
Nonincendive flashlight for use when inspecting areas full of flammable gas
A Metalsub cable diving torch
