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Case Study 2 - Backlight Design

This customer approached us with the need for a monochrome LCD design to fit into their area/personal monitoring devices. With their end product to be utilized as a safety device in a highly regulated work environment, the LCD design met specific voltage and current restrictions. With the LCD being integrated into a designed product, the total LCD thickness was limited to 2.5 millimeters.
The customer’s additional requirements added that the LCD have a very minimal backlight luminance while still allowing text legibility at a 3 feet viewing distance, in complete darkness. The final product would spend considerable time in high bright, outdoor conditions, so the LCD must also be clearly viewable in sunny and ambient lighting.
An obstacle with this selection, however, is the Sharp panel’s high reflectance, which inherently permits very low transmissivity, at 0.25%. This panel is generally used without a backlight added to it.
This customer had a time requirement and had allotted 8 months for development time.

A secondary challenge involved ensuring the ease of integration with the customer’s existing system, which would require a 24V interface solution for the backlight power supply. This necessitated the engineering of a custom designed LED interface board, which would allow for the seamless transition from CCFL to LED backlighting.

PRODUCT
4” SHARP MONOCHROME HR-TFT DISPLAY BACK- LIGHT DESIGN

VALUE ADDS BACKLIGHTING, ENHANCEMENT FILMS

INDUSTRY
MINING, OIL AND GAS SEGMENT

APPLICATION
AREA MONITOR, PERSONAL MONITORS

Solution

The customer specifically selected the 4” Sharp monochrome HR- TFT display for its ability to view the LCD screen in ambient light. With the selection of an 800 nit backlight, AGDisplays was able to stay well below voltage and current requirements. Specifically, the voltage and current requirements were met because of the high output LED and the addition of the light guide material, that boosts luminance without adding more power consumption. The 800 nits was filtered through the .25% transmissivity of the Sharp LCD, yielding 2 nits to achieve the desired viewability.

We also included the addition of an optical diffuser film to help bal-ance uniformity throughout the viewing area. The optical diffuser film brought the brightness uniformity to 82%. The additional opti-cal diffuser film added a negligible amount of thickness to the overall build.

This project took 6 months of development time, from concept to production volume, which stayed well within the customer’s ex-pected development time. This project is expected to yield 2000 units a year over a period of 10 years.

This design has yielded an extremely low fall out rate at 0.02% total over the first 7 years.

Summary

  • All customer requirements were met.
  • Exceeded development and production time
  • Extremely low fall out rate at 0.02% for design

Design Considerations

AGDisplays met viewability requirements in zero-to-low light environments, as well as viewability requirements for sunny and ambient environments.

Customer had specific voltage and current limitations due to safety regulations; AGDisplays met these with high output LED rails and the aid of a light diffuser to enhance output.

The selected Sharp 4” monochrome LCD is considered to have very low transmissivity that was counteracted with the 800 nit LED rails.