Modern passenger aircraft employ a variety of different display technologies on the flight deck, including those based on conventional cathode ray tubes (CRT), light-emitting diodes (LED), and liquid crystal displays (LCD).
Display Technologies Compared
1. CATHODE RAY TUBE (CRT)
Advantage
- Well proved technology
- High resolution and contrast
- Wide range of colors
- High brightness
- Wide viewing angle
- Low cost
- Potential for ‘thin’ display units
Disadvantage
- Heavy and bulky
- High voltage
- High power consumption
- High temperature
- Sensitive to external electromagnetic effects
- Affected by bright light
- Vulnerable to shock, vibration and catastrophic failure
2. LIQUID CRYSTAL DISPLAY (LCD)
To overcome the disadvantages of the CRT the Liquid Crystal Display (LCD) was developed. It is small, light with a low power requirement, and is used on flight decks and passenger entertainment systems.
Advantage
- Low voltage and power
- High resolution
- High contrast in high ambient light
- Non catastrophic failure
Disadvantage
- Slow response at low temperature
- Has to be backlit in low ambient light
- Narrow viewing angle
- Limited display size
- High cost and circuit complexity for full color
3. LIGHT EMITTING DIODE (LED)
An LED consists of a junction diode made from the semiconductor compound gallium arsenide phosphide. It emits light when forward biased, the color of the light emitted is in direct proportion to the current flow. Light emission in the red, orange, green, and yellow regions of the spectrum is obtained depending on the composition and impurity content of the compound.
In applying this to aircraft displays either the 7-segment or dot-matrix configurations may be used. In the 7-segment display for numerical indication, each segment is an LED mounted within a reflective cavity with a plastic overlay. Depending on which segments are energized, the display lights up the numbers 0 to 9. Note that the number 8 uses all segments of the display. The display typically uses a 5V supply.
In a dot matrix display, each dot making up the numbers is an individual LED. The size of the matrix determines how many LEDs are used.
Advantage
- High display brightness
- Wide viewing angle
- Well proved technology
- Extensive application
- Low voltage operation
Disadvantage
- High power demand
- Low resolution
- Not yet suitable for large arrays
