Pen lights allow users to focus a small beam of light on an object. This is useful for technicians that need to see a specific area of an item that needs repair and medical personnel who want to gauge pupil reaction times. Pen lights are convenient for users because they slip in a pocket or other small place without taking up much room. Pen lights receive power from either AA or AAA batteries or button cell "watch type" batteries.
Open the battery compartment by unscrewing the bulb end of the light. Turn the light end counterclockwise to remove it from the base.
Remove the old batteries. When you remove the batteries, pay attention to which direction they are pointing.
Insert the new batteries. Make sure the new batteries point in the same direction as the old batteries.
Clean the screw area before you replace the head of the light.
Replace the light by screwing it clockwise into the base.
If you are not going to use the light for an extended period, remove the batteries before storing the light.