Penlights are used in many walks of life and in many situations. They vary in size from two to five inches in length and are normally powered by two AA or AAA batteries. This makes them very portable and also very light. Their greatest benefit is its ability to illuminate a very specific area with a very bright light making it more of a specialist tool than a general use one.
Doctors of every type from dentists to general practitioners to surgeons use penlights when examining patients as there size makes them convenient to use. They can be used to check areas of the mouth and throat, examine wounds and to assess pupil response. Some penlights are even purpose built for use in hospitals and come with a tongue depressor built on to them to ease examining the throat.
For many of the same reasons as doctors, nurses also use penlights. As they spend a lot of their time monitoring patients they tend to use penlights to assess the patient's progress rather than as an examining tool used to help diagnosis.
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The main purpose for the police to use penlights is to check pupil response to see if a suspect is under the influence of drugs or alcohol. Penlights are very useful in this area as, along with its portability, it directs a very direct spot of light.
When checking an engine it can often be difficult to see certain areas, even in a well lit room and the different parts of the engine cast shadows onto others. In certain situations mechanics must use penlights to accurately position an area on light to help identify problems, although in some situations spot lights will simply be placed both under and above the car to achieve this.
Portability is a major factor in the extended use of penlights in many walks of life. Many of these miniature torches are designed to fit comfortably in a pocket or even on a key chain. The bright, accurate and controllable spot of light also makes it useful for looking for items lost under furniture, checking household plumbing and electrical sources.
The penlights main problem is that it is no good at illuminating a large space, unlike a normal torch. The spot of light is very focused and has been designed to shed light on a very small area meaning its benefits are often counteracted by its shortfalls. It can be a very useful tool to have, but it by no means works in every situation.