---
title: "Short note: Flat panel displays"
subject: "Computer Graphics"
chapter: 1
key: "semester_5/computer_graphics:short-note-flat-panel-display"
source: https://www.bctengineer.com/q/semester_5/computer_graphics/short-note-flat-panel-display
site: BCT Engineering
---

# Short note: Flat panel displays

Computer Graphics · Chapter 1: Introduction and Application

- Asked in: 2067 Mangsir (old course), 5 marks; 2066 Magh (old course) (asked 2 times)
- Video: [flat panel display in computer graphics: Plasma Display panel, Liquid crystal display & LED display](https://www.youtube.com/watch?v=QzPb_yCbRhQ) — QuickCS
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/computer_graphics/short-note-flat-panel-display
- Whole chapter: https://www.bctengineer.com/md/semester_5/computer_graphics/chapter-1

## Question

Write a short note on flat panel displays.

## Short answer

Flat panel displays are thin, lightweight, low‑power devices. Emissive types (plasma, OLED) generate light directly; non‑emissive types (LCD) modulate a backlight. They offer sharp, geometrially correct images but may have limited viewing angles and fixed native resolution.

## Answer

**Flat panel displays** are video devices that are much thinner, lighter and consume less power than a CRT. They are used in laptops, mobiles, TVs and monitors. They are divided into two classes.

#### Emissive displays
These convert electrical energy into light themselves.
- **Plasma panel:** gas (neon-xenon) between two glass plates with a grid of vertical and horizontal electrodes; a voltage at a crossing makes the gas glow.
- **LED / OLED:** an array of light emitting diodes or organic layers; each pixel emits its own light.
- **Thin-film electroluminescent display:** phosphor layer glows when voltage is applied.

#### Non-emissive displays
These use light from outside (backlight or room light) and modulate it.
- **LCD (liquid crystal display):** liquid crystal between two polarizing plates; applied voltage changes crystal orientation, controlling light passing through. A backlight (CCFL or LED) is used.

```text
Backlight -> Polarizer -> Liquid crystal -> Polarizer -> Eye
                          (voltage per pixel)
```

**Advantages:** thin, light, low power, no flicker or geometric distortion, sharp image.
**Disadvantages:** limited viewing angle (LCD), costlier, fixed native resolution.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Flat panel displays are divided into which two classes?
   A. Vector and raster
   B. Active and passive CRT
   C. Monochrome and colour
   D. Emissive and non-emissive
   Answer: D. Emissive produce light; non-emissive modulate external light. (Key point: Classification)

2. Which is a non-emissive display?
   A. LCD
   B. Plasma panel
   C. OLED
   D. Thin-film electroluminescent display
   Answer: A. LCD modulates backlight and does not emit light itself. (Key point: Non-emissive example)

3. How does an LCD control the light reaching the eye?
   A. Gas glows at electrode crossings
   B. Voltage changes the crystal orientation between two polarizers
   C. Phosphor glows under voltage
   D. An electron beam strikes the phosphor
   Answer: B. Applied voltage reorients liquid crystal, changing light passed through polarizers. (Key point: LCD working)

4. Which is a disadvantage of flat panel displays listed?
   A. Heavy and bulky
   B. Geometric distortion
   C. Limited viewing angle (LCD) and fixed native resolution
   D. High flicker
   Answer: C. They are thin and flicker-free but have viewing-angle and fixed-resolution limits. (Key point: Disadvantage)

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