The video begins by introducing the light pen and the zapper gun, two technological devices from the 1980s that were used for drawing and gaming respectively. Both devices work by sensing light but have different mechanisms.

• The light pen is a pointing device used for drawing and general operating system usage.
• The zapper gun is a light gun used with some games on the Nintendo and most other 8-bit systems.

The light pen works by detecting the light from a CRT screen and transmitting its position to the computer. It doesn't track where it is on the screen, but rather when it is, based on the pixel it has lit up and the exact time.

• The light pen contains a lens and a photo sensor. When placed up to the screen, the computer immediately knows where on the screen it is pointing.
• The computer doesn't know where the light pen is on the screen, but when it is, based on the pixel the pen has lit up and the exact time.
• The light pen can see the pixel underneath the lens when it lights up, transmitting that information to the computer, which then knows exactly which pixel it was drawing at the time the signal comes in.

Despite its innovative design, the light pen has several limitations, including its accuracy and compatibility issues with different software. It also does not work on LCD screens.

• The light pen has issues with accuracy and often sends inaccurate results, leading to jagged edges when drawing by hand.
• Not all software is compatible with all light pens due to differences in the wiring of the button from one light pen to the next.
• The light pen has trouble positioning the pointer over a black area of the screen because when there are no pixels being lit up, it can't see anything.
• The light pen only works on CRTs and is useless on LCD screens due to differences in how they draw the screen.

The light pen was not popular during the 1980s due to its accuracy problem, compatibility issues, lack of strong operating system support, and physical discomfort when used for prolonged periods.

• The light pen's accuracy problem, which makes it hard to do pixel-perfect drawings, led to artists preferring keyboard or joystick controls.
• The light pen's compatibility issues meant that the software users wanted to use might not work with their light pen.
• Add-on input devices like the light pen rarely catch on unless there are killer apps, games, or strong operating system support.
• Using the light pen was physically uncomfortable due to having to stretch the arm out to the TV or monitor.

The zapper gun, unlike the light pen, does not track the beam of the CRT. Instead, it senses a white flash of light on the screen during a specific frame to determine if a hit was made.

• The zapper gun works by sensing a white flash of light on the screen when the trigger is pulled.
• If the gun is aimed correctly, it will see the light. If not, it won't.
• The gun doesn't know where it is looking on the screen; it only knows whether it saw a flash of light or not.

The zapper gun saw limited use due to factors such as the low replay value of games, the need for additional accessories, and the physical discomfort of using the gun for extended periods.

• Light gun games, while fun to play, often had low replay value, limiting their popularity.
• The gun was an additional accessory, meaning game developers who supported the light gun would likely sell fewer games, as fewer households would have the accessory.
• Using the zapper gun for extended periods could be physically uncomfortable, similar to the light pen.

The proliferation of LCD monitors and televisions made both the light pen and the zapper gun obsolete. The different image processing of LCD screens compared to CRT screens rendered these technologies ineffective.

• The light pen and zapper gun were rendered obsolete by the advent of LCD screens.
• The light pen doesn't work on LCD screens because there's no single pixel, electron beam scanning across to pick up to know where it is looking at on the screen.
• The zapper gun doesn't work on LCD screens because there's a millisecond delay between when the signal goes to the TV and when the TV actually displays it, disrupting the timing of what the Nintendo is looking for in regards to the flashes of light.