Sun-readable display technology: How it works

As more processes are controlled by HMI, market demands for outdoor LCD applications are increasing. Beijer Electronics has released the Exter Sun-Readable HMI range, an optimal combination of technologies suitable for petrochemical and waste treatment fields. Tutorial of related technologies follows, with photo.
By Control Engineering Staff October 14, 2008

Schaumburg, IL – As more processes are controlled by HMI, market demands for outdoor LCD applications are increasing. Beijer Electronics has released Exter Sun-Readable HMI products, an optimal combination of technologies suitable for petrochemical and waste treatment fields. Tutorial of related technologies follows, with photo.

Beijer Electronics released Exter Sun-Readable HMI.

Tutorial of technologies for LCD screens in the sun
Sunlight visibility of a display depends on differences between the lumination (brightness) and the illumination (ambient light shining on a display). Lumination is the amount of light energy emanating from the display (expressed in Cd/m2). The readability depends on the amount of light being reflected off the display. The simplest way to enhance visibility is to increase brightness. A standard screen emits 350 Cd/m2. Some offers on the market feature 8,000 Cd/m2. The result is good, but because of the added lamps, high bright LCDs have disadvantages including high power consumption, excessive heat generation, increased dimensions, electrical circuit reliability problems, and shortened LCD lifetime.
A second option is transflective technology. Some TFT LCDs are provided with a reflective mode of illumination without compromising transmissive illumination. With imposed reflective function, modified LCDs reflect ambient light passing the LCD cell and use reflected light beams as illumination. The stronger the ambient light, the brighter the LCD appears. The modified LCD is viewable under all lighting conditions including direct sunlight regardless of the LCD’s original brightness. However, a regular transmissive LCD is difficult to read under strong ambient light without direct sunlight. Problems noticed in transflective LCDs include a narrow viewing angle, discoloration, low brightness, and loss of contrast.
The high bright LCD and the transflective LCD are solutions generally used for outdoor applications. However, both solutions are not really suited for industrial use. It is necessary to take another route in trying to control reflected lights. As light transfers from one material to another, such as air to glass, differences in the index of refraction will cause reflection. On an LCD screen, cumulative reflection of the different surfaces is nearly 15% of ambient light. If the total reflection is close to the display
Bond technology is a third option. It enables coupling of the front glass and the internal glass, but the cost is high compared to what it brings in terms of quality. Features include a standard display, an enhancement film applied on the internal screen improving brightness and contrast, and a polarizing film applied on both sides of the touchscreen to reduce light reflection. The design includes a gap of 1.5 mm, between the two screens. This distance has the effect of reducing Newton rings or the circular rainbow effect which may be caused by non-uniform cell thickness, as well as other defects resulting in a flat surface in contact with a slightly curved one.
Brightness is better than a standard screen (550 Cd/m2 instead of 350 Cd/m2 for a standard Beijer Electronics screen). The touchscreen features anti-glare and reflection surface treatments. Anti-reflective coated protection glass minimizes mirror image and maximizes transmittance. Anti-glare coated protection glass scatters light directed on the surface and softens the image of direct light sources visible in the reflection of the viewing area.
About the Beijer offering, Exter Sun-Readable displays

Exter Sun-Readable displays are manufactured in a cleanroom in order to eradicate dust problems. “We also feature a 100% dimmable screen, so our customers can use it in any light conditions, 24 hours a day,” says Pelle Johnsson, global product and marketing coordinator for marine products. Normal screens change the color of the display when brightness is decreased. A 100% dimmable screen offers a real brightness decrease without compromise to quality. Beijer’s in-house inverter does this. All LCD backlights powered by cold cathode fluorescent lamps (CCFL) require inverters, electronic circuits that transform a dc voltage to an ac voltage, which drive the cold cathode fluorescent lamps (CCFL). Dimming capabilities are beneficial because lowering backlight luminance will lengthen backlight life.
Also read: Agreement: Alfa Laval processing equipment to get Beijer HMIs
– Control Engineering News Desk
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