LCD Backlighting for Digital Signage Displays
LCD Backlighting for Digital Signage Displays
Digital signage displays have been used extensively in outdoor advertising, but a fundamental problem has arisen with the brightness of the displays. LCD displays are non-emissive and thus, they do not self-generate a light source. Their visibility must come from some external lighting source. There are currently three main types of visibility technologies: - Reflective LCD Visibility - This is where the LCD display relies on an external light source from in front for visibility. The ambient light enters the front of the display, and is controlled by a diffuser. This technology is used in calculators and wristwatches.
- Transmissive LCD Visibility - This technology is the opposite of reflective visibility. It relies on the positioning of a light source behind the LCD panel. This method projects light colored objects against a dark background. This technique in turn produces a sharper, and more contrasted image. This is also known as negative mode broadcasting. This technology is used in laptop computers, audio devices, and automotive display components.
- Transflective LCD Visibility - This technology combines both reflective technology and transmissive technology. It enables light to pass through from the back of the LCD display, as well as to reflect from the front. This technology is used in cell phones, PDAs, and GPS displays. The transmissive light is usually attached to a rear polarizer, allowing light to flow through both the back and the front of the display. This is becoming the most popular format.
Sometimes an external light source can be something completely separate from the signage equipment itself, and can already be found naturally in the installation environment. It may come from existing light sources such as a lamp or an alternate form of projected artificial lighting. It may also come from the sun. If you can incorporate this in to the planning and layout of your digital signage installation, you can greatly increase the readability of your LCD display. Backlighting is an already popular method of increasing the readability of your display. There are a few common technologies for used to accomplish this task, and we'll discuss three of them here. - Light Emitting Diode. (LED) - The most common backlighting form used in mobile phones, the Light Emitting Diode is beneficial over the Electroluminescent Lamp technologies. LED lighting does not require an inverter for a power source. All they require is a DC source of +3VDC~+5VDC. They are extremely bright depending on the configuration and they have a lifespan exceeding 50,000 hours.
- Electroluminescent Lamp. (EL) - The advantages of this type of light source are that the backlight is extremely thin and that they have a relatively low cost compared with other sources. Unfortunately, the Electroluminescent Lamp does not perform well in highly humid conditions, which rules it out completely for some un-conditioned climates. In high humidity, the unit delaminates and begins to malfunction. Additionally, this type of backlight requires that DC power be converted to AC power, and thus, needs a unit called an inverter.
- Cold Cathode Fluorescent Lamp. (CCFL) - The Cold Cathode Fluorescent Lamp is most commonly found in graphics and color displays. It offers a bright white light that is uniform throughout. Industrial PCs, laptop computers, gas pumps, and medical instruments are all common applications of this device. The drawback of this technology is that it also requires DC power to be converted to AC power, and thus, needs a unit called an inverter.
When you are purchasing your next digital signage installation, sit down with your provider and discuss the various equipment choices that are available, and how their placement will affect their visibility and readability. With this information, you'll be more prepared to make a well informed decision.
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