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Designing a Sunlight Readable LCD

Designing a Sunlight Readable LCD

Aug 27th 2021


The term "sunlight-readable" refers to a display that can be viewed in bright light, such as direct sunlight. Standard, off-the-shelf displays are difficult to see in direct sunlight because the brightness of the sun is substantially higher than that of the display. The visuals on the screen are washed out by reflections on the monitor. Outdoor applications, vehicle infotainment systems, and public kiosks frequently demand sunlight viewable displays. The best display technology for outdoor viewing is one that offers between 800-1000 nits of brightness, whilst the typical display only offers between 250 – 450 nits.

Two common methods are used to ensure display readability. The first is choosing the ideal polarizer material and ensuring the backlight is adequately powerful while also maintaining power efficiency and avoid a heat-related meltdown of the unit. Ensuring that the backlight does not result in overheating is crucial because sustained warmer temperatures can result in premature delamination of the LCD unit.

Out of the three types of polarizers used, reflective polarizers are the best choice for sunlight readability is just a mirror put to the glass's bottom layer. It reflects all the light that enters through the top layer of glass back to the user making it easier to read the display in bright sunshine.

Unlike a reflective polarizer, a transmissive LCD polarizer does not reflect any light. The backlight must provide all the illuminations. The user receives 100% of the backlight that passes through the bottom and top layers of glass. For the display to be readable, the backlight must be turned on. Ambient light from office lights or sunshine passes through the bottom layer of glass and does not reflect the top layer, so sunlight illuminates the display just slightly. The display becomes more washed-out as the sun becomes brighter. A Transmissive display should have a brightness of 800 NITs or above as a rule. For reference, an NIT is the amount of light produced by a single candle.

The Reflective and Transmissive polarizers are combined in the Transflective LCD polarizer. It reflects some of the ambient (sun) light that passes through the front of the glass while also allowing some backlight light to get through to the front layer of glass. It works well in direct sunshine, although it lacks the contrast of a Reflective polarizer.

The next method of improving display readability is to increase the brightness of the backlight. Additional LEDs in the backlight can substantially increase the power consumption of the display which can result in a shorter operating duration for battery powered applications. To shed more light, the increased power consumption may result in device overheating and if not managed well when creating the LCD design, can result in damages to, or a reduced lifetime for other components in the system. Also, it is important not to power the backlight beyond the specified current levels in the LCD design. Doing so will result in a reduction of the LED’s half-life. Finally, displays that are intended for use in daylight and at night may result in eyestrain if brightness is not adjusted as the day progresses.

Finally, a great way to ensure the display is readable in bright situations is to avoid glare. This can be done by using an OCA bonding if the display has a cover glass, or perhaps by coating the display itself in an anti-reflective coating. Such coatings can reduce eye strain, headaches, and poor visibility. An AR coating is overlaid on the display and is made of an extremely hard thin film. It's constructed of a substance with a refractive index that's midway between air and glass. As a result, the light reflected from the inner surface and the light reflected from the film's outer surface is virtually identical in intensity. The two reflections from each side of the film virtually cancel one other out through destructive interference when applied in a thickness of about a fourth of the wavelength of light, decreasing the glare you see.

Sunlight readable LCDs are becoming increasingly popular due to their brightness and versatility in different environments. Focus LCDs offers a broad selection of sunlight readable displays that can be customized to your specific requirements. Find out how we can brighten up your product by contacting us today! 

Resources:

  1. https://unsplash.com/photos/ULJCBY8Tcfg?utm_source...