← IGCSE Computer Science Paper 1

LED screen

A screen that uses light emitting diodes as its light source, as a backlight for an LCD panel or as the pixels themselves. It is bright, thin and uses little power.

Part of: IGCSE Computer Science 0478 — 3.2 Input and Output Devices — Module 20

Understanding LED screen in IGCSE Computer Science Paper 1

What it does: LEDs are very small, so the light layer can be much slimmer. This lets TVs and phones be made thin. In large LED billboards every pixel is an LED that makes its own light. This makes the screen bright enough to see in daylight. LED stands for light emitting diode. LED screens use these as their light source, while older LCD screens often used fluorescent (CCFL) backlights. In many LED screens the LCD panel makes the image and LEDs behind or beside it provide the light, so it is an LED-backlit LCD. LEDs are energy efficient, so LED screens use less power. This helps phone battery life and lowers electricity costs.

Common mistakes: An LED screen uses light emitting diodes as its light source. Fluorescent tubes were used in older LCD backlights. Line 3 should be light_source = "diodes". Line 1 uses == (comparison) instead of = (assignment). backlight is never given a value, so the program crashes. It should be backlight = "LED".

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This module's key terms are also in a printable crossword (Modules 262–272) and word search (Modules 262–282).

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Learning
Duo
What does an LED screen use as its light source?
Light emitting diodesCold cathode fluorescent lamps
Matches
LED screen: power use = very high
↓
LED screens use LOW power, not high power. This is one advantage over older backlights.
Applying
Meanings
Term
LED screen
Meaning
A screen that uses light emitting diodes as its light source, as a backlight for an LCD panel or as the pixels themselves. It is bright, thin and uses little power.
Practice
LED screen: uses light emitting diodes as its light source
Testing
Gaps
"LED screens are bright and thin"
Check Answer
Spots
2panel = "LCD"
3light_source = "fluorescent tube"

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Quick Questions

1. What does an LED screen use as its light source?
A. Cold cathode fluorescent lamps
B. Light emitting diodes ✓
LED stands for light emitting diode. LED screens use these as their light source, while older LCD screens often used fluorescent (CCFL) backlights.
2. Most LED TVs and phone screens are best described as:
A. An LCD panel lit by LED backlights ✓
B. A screen with no LCD panel and no backlight at all
In many LED screens the LCD panel makes the image and LEDs behind or beside it provide the light, so it is an LED-backlit LCD.
3. Which statement about LED screens is correct?
A. They can be thinner than older backlit screens ✓
B. They must be thicker because LEDs are large
LEDs are very small, so they allow brighter and thinner screens than older backlights.
4. Compared with older backlights, LED backlights use:
A. Less power ✓
B. More power
LEDs are energy efficient, so LED screens use less power. This helps phone battery life and lowers electricity costs.
5. In some LED screens, what do the LEDs act as?
A. Only the screen's speakers
B. The pixels themselves ✓
In some LED displays each tiny LED is a pixel that makes its own light. Others use LEDs only as a backlight for an LCD panel.

Match the Pairs

LED-backlit LCD → An LCD panel that has a layer of light emitting diodes behind it to light up the picture
LED backlight → A bright, thin light source made of light emitting diodes that uses less power than older backlights
An LED screen is thinner than an older screen with a bulb backlight because LEDs are tiny → screen.thickness = thin
Big outdoor billboards can use LEDs as the pixels themselves, so each pixel makes its own light → pixel = LED
LED screen: power use = very high → LED screens use LOW power, not high power. This is one advantage over older backlights.
LED = Liquid Emitting Display → LED stands for Light Emitting Diode, not Liquid Emitting Display. The diode is the light source.

Key Term

LED screen
A screen that uses light emitting diodes as its light source, as a backlight for an LCD panel or as the pixels themselves. It is bright, thin and uses little power.

Fill in the Blanks

1. OUTPUT "LED screens are bright and thin"
Hint: Type the pseudocode keyword that displays a message to the user.
2. IF backlight = "LED" THEN
Hint: Type the keyword that starts a selection statement checking the backlight type.
3. IF powerUse = "low" THEN OUTPUT "LED backlight saves energy" ENDIF
Hint: Type the keyword that comes after the condition and begins the action to run when it is true.
4. IF type = "LED" AND thin = TRUE THEN OUTPUT "Slim LED TV" ENDIF
Hint: Type the logical operator that needs both conditions to be true.
5. IF pixels = "LED" THEN OUTPUT "Billboard screen" ENDIF
Hint: Type the keyword that closes the selection statement.

Spot the Error

Question 1
A screen = "LED"
B panel = "LCD"
C light_source = "fluorescent tube"
Line C — An LED screen uses light emitting diodes as its light source. Fluorescent tubes were used in older LCD backlights. Line 3 should be light_source = "diodes".
Question 2
A backlight == "LED"
B if backlight == "LED":
C power = "low"
D print(power)
Line A — Line 1 uses == (comparison) instead of = (assignment). backlight is never given a value, so the program crashes. It should be backlight = "LED".
Question 3
A thickness_mm = 8
B thin = thickness_mm > 10
C if thin:
D print("LED is thin")
Line B — LEDs give thinner screens, so a thin screen has a small thickness. Using > makes thin False for 8 mm. Line 2 should use < 10.
Question 4
A uses = []
B uses.append("TV")
C uses.append("phone")
D uses.add("billboard")
Line D — Python lists do not have an add method. Use append to add LED screen uses such as TVs, phones and billboards. Line 4 should be uses.append("billboard").
Question 5
A led_watts = 40
B old_watts = 100
C saving = led_watts - old_watts
D print(saving)
Line C — LED backlights use less power than older backlights. The saving is old power minus LED power. The broken line gives a negative saving. It should be old_watts - led_watts.

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