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What is a Light Pen?

Nowadays, everyone uses touchscreen devices, and devices without touchscreens are considered almost obsolete. Would it interest you to know that there was once a device that allowed users to select displayed objects and make gestures on a screen but with better positional accuracy? Yes, that’s right. It’s the light pen.

The light pen is a photosensitive computer input device that allows users to interact with the elements on a computer screen. Some of these include selecting texts, drawing images, highlighting, and so on. Asides from the generic definition of a light pen above, the term could also be used in two distinct instances.

A light pen may also refer to a light pointing device commonly used during a PowerPoint presentation. In this context, it could likewise be referred to as a laser pointer. It is used to direct the viewer’s attention to a specific area in the presentation. A light pen may also refer to the digital pen commonly known as a stylus used on a graphics tablet.

However, in this article, our focus would be on the first generic definition. We would also be considering its brief history as well as how it can be operated.

History of the Light Pen

Just as you were hinted earlier, a light pen can be considered the predecessor to popular touchscreen technology. It was first created in 1955 as part of MIT’s Whirlwind Project, but it became common in the 1960s when graphic terminals (such as IBM 2250) were released. In the 1980s, the device’s usage likewise spread to text-only terminals as well as home computers, such as Atari.

However, the light pen mode is not compatible with the modern LCD screens we have today. This is the reason why the rather impressive input device eventually died out. Want to find out its working mechanism, which eventually made it incompatible with the modern touch screen technology? Read on!

How the Light Pen Works

The light pen works by detecting the change in the brightness of nearby pixels. During its usage, the light pen worked best with CRT monitors because of the way such monitors scan the screen (one pixel at a time). A change in the brightness of nearby pixels indicates that the cathode ray tube beam is scanning that area.

As a result of the scanning method of CRT monitors, it allows the light pen to send this event’s timing to the computer. The computer, in turn, compares this information to the timestamp of the last electron beam scan. This then allows the computer to infer the exact location of the light pen and give the appropriate response to the user.