Oct 21 2007
Image Credit: Brian A Jackson/Shutterstock.com
Article updated on 03/03/20 by Stephen Edgar
Types of LCD Backlights
- LED Backlighting
- Electroluminescence Panel (ELP) Backlighting
- Cold Cathode Fluorescent Lamp (CCFL) Backlighting
- Woven Fiber Backlighting
- Incandescent Backlighting
LCD vs OLED
What is LCD backlighting and Why is it Used?
Liquid crystal displays do not generate light. Think of them as an array of blinds that allow light through when open and not when closed. When ambient light is insufficient, backlighting must be used. There are several backlights available for LCDs, the choice of which to use depends on the features, appearance, and cost.
Types of LCD Backlights
Each LCD backlighting system has its advantages and disadvantages, and there is no one method that is suitable for all applications. The 5 most common backlights for LCDs are:
LED Backlighting
- Electroluminescence Panel (ELP) Backlighting
- Cold Cathode Fluorescent Lamp (CCFL) Backlighting
- Woven Fiber Backlighting
- Incandescent Backlighting
LED Backlighting
LED or light-emitting diode backlight is one of the most common backlighting for small and medium LCDs. LED backlighting offers the following advantages: it is low cost, long life, unaffected by vibration, and it can be dimmed by controlling the voltage to improve power consumption. Despite its many benefits, LED also has disadvantages. The main being that it does require more power and this becomes more significant as the size of the LCD increases.
Several colors are available for LED backlights, the most common being yellow-green, and now white is cost-effective and very popular. As stated earlier, LED backlights offer a longer operating life with a minimum of 50,000 hours. There are two basic configurations for LED backlight; they are array and edge-lit. With both types of LED configurations, the light source is focused into a diffuser that distributes the light evenly behind the viewing area.
In Array lit configuration, a large number of LEDs are mounted uniformly behind the display. It offers more uniform and brighter lighting but consequently, consumes more power. In Edge-lit configuration, LEDs are mounted to on-side focused edge-on into the diffuser. This configuration offers a thinner package and it uses less power than the array lit configuration.
Electroluminescence Panel (ELP) Backlighting
Electroluminescence Panel backlighting, or commonly abbreviated as EL or ELP, is a solid-state phenomenon that uses colored phosphors instead of heat to generate light. ELP backlights are very thin and lightweight and also provide an even light distribution.
They are also available in several colors; the most popular for use with LCDs is white. The drawbacks that have caused ELPs to decrease in popularity is their limited life of 3,000 to 5,000 hours to half brightness, the need of an inverter to convert DC to AC, and because they generate electrical noise that can interfere with other circuitry.
Cold Cathode Fluorescent Lamp (CCFL) Backlighting
Cold Cathode Fluorescent Lamp backlighting, or commonly abbreviated as CCFL, offers low power consumption and a very bright white light. Edge lighting is the primary CCFL configuration used in LCD backlighting. A cold cathode fluorescent lamp is the light source that distributes the light evenly across the viewing area using a diffuser.
CCFL backlighting is mainly used in graphic LCDs. CCFL has a longer life compared to electroluminescence panel backlighting with a minimum of 10,000 to 20,000 hours. However, the main disadvantage of CCFL is that the light output is governed by temperature, in cold conditions the light output by as much as 60%. The other drawbacks are that the intensity of light cannot be varied, and also a reduction of the life expectancy of up to 50% may be expected due to vibration.
Woven Fiber Backlighting
An extremely uniform backlight is provided by woven fiber optic mesh backlighting. The lifetime is dependent on the type of bulb used. The bulbs are usually mounted away from the LCD, where if necessary can be easily replaced. Halogen and LEDs are mainly used as a source of light. Woven fiber optic panels tend to be somewhat expensive. The uniformity and brightness are worth the extra cost for some applications.
Incandescent Backlighting
Incandescent Lamp backlighting is only used where cost is a major issue. Incandescent lights are very bright, but the downside is that they are not uniform. Incandescent lights also generate a large amount of heat, have a short life expectancy, and consume a lot of power to achieve brightness. They can provide very white light but by varying the voltage, different colors can be produced. The other setback for incandescent lights is that they can be sensitive to shock and vibration.
LCD vs OLED
Organic Light Emitting Diode or OLED displays began to appear in small consumer appliances like cameras and mobile phones in 2002. The superiority of this new technology ensures that it is already replacing LCDs in many applications including newer, high-end mobile phones.
The different manufacturing process to fabricate OLEDs offers many advantages over flat-panel displays made with LCD technology. OLEDs can hypothetically have a significantly lower manufacturing cost than LCDs or plasma displays since OLEDs can be printed onto any suitable substrate using an inkjet printer or even screen printing technologies. New applications such as roll-up displays and displays embedded in clothing can be made possible by printing OLEDs onto flexible substrates.
A greater range of colors, brightness, as well as a larger viewing angle than LCDs are offered by OLEDs. OLED pixels also directly emit light, eliminating the need for backlighting. OLED pixel colors appear correct, even as the viewing angle approaches 90 degrees from normal. Since LCDs require polarizers to filter out about half of the light emitted by the backlight, this results in energy being wasted. Also, color filters eliminate about two-thirds of the light in a color LCD.
OLEDs respond faster than normal LCD screens and an average of 8 to 12 milliseconds in response time has been recorded in a normal LCD compared to 0.01 milliseconds in response time has been recorded with an OLED.
In summary, OLED displays offer significant advantages over LCDs, such as no backlighting being required. The size of OLED displays is also smaller than compared to LCDs and they use less power.
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