7 Misleading Assumptions About Sunlight Readable LCDs

2 Jun 2017

What determines if a display truly is sunlight readable?

Most consumers would be surprised to learn that:

1) There is no universal definition for “sunlight readability” of LCDs.
2) There is no governing certification agency, therefore no performance testing or certification is required for suppliers to claim that their panels are sunlight readable.
3) There is no oversight committee that protects the consumer from false or misleading display performance claims.
4) LCD OEM and Value-Add Reseller (VAR) data sheets provide metrics such as maximum brightness and contrast; however, these attributes are impractical for gauging the LCD’s effectiveness in direct sunlight, since they reflect optimal performance while measured in a dark room.
5) There is no direct LCD performance correlation between dark room and direct sunlight performance.
6) Given two displays similarly measured as 1,000 nits, for example, and considered sunlight readable in a dark room, either one may have insufficient contrast to be readable in direct sunlight.
7) Typically, LCD OEMs and VARs do not provide consumers with practical metrics that indicate the panel’s performance in direct sunlight, such as Weber Contrast.

The consumer who needs a sunlight readable panel is left with little choice but to accept a supplier’s subjective opinion, place trust in ambiguous and misleading performance data, or endure the costly and time-inefficient process of trial and error evaluation…that is, until now!!

A small excerpt of specifications from a typical Display Head Assembly data sheet

Figure 1: Sample Data Sheet Excerpt

General Digital has standardized the quantification of its value-add display performance so that consumers can more easily select a panel that meets their specific needs. This simplified process also allows consumers to feel confident that they have made an informed purchasing decision when choosing one of our value-add sunlight readable display solutions; it eliminates the guesswork, anxiety and trepidation previously associated with the process. Consumers need only view General Digital’s innovative and user-friendly sunlight readable classification metric (Weber Class) provided on our data sheets and compare it to our Weber Class Application Table (see Table 1) to determine a display’s practical usefulness and performance limits in direct sunlight. Table 1 is derived directly from the MIL-L-85762A document. Note: Although MIL-L-85762A has been superseded by MIL-STD-3009, much of the Weber contrast data was not carried over to the new documentation.

Photo of Photometric Test Setup

Figure 2: MIL-L-85762A Optical Test Bench at General Digital

General Digital did not create a new optical measurement system; that would be tantamount to claiming that we invented the Internet! Instead, we adopted the US Military’s MIL-L-85762A procedures for testing and evaluating display performance in direct sunlight into our own qualification and testing procedures in lieu of an industry standard.  Our value-add display solutions are tested in our own Optical Laboratory, under a well-defined, consistent and controlled lighting environment that simulates worst-case exposure to sunlight.

There are six Weber Classes of contrast, each assigned a numeric value from 1 to 6, where Class 1 represents the poorest performance (in environments with high ambient lighting) and Class 6 represents the best. Each class is assigned a range of Weber Class values, as well as the type of visual information that can be practically displayed under the worst-case lighting conditions, as defined by MIL-L-85762A. With each increase in Weber Class, the display accumulates the performance attributes of the previous classes. For example, a display that achieves a Weber Contrast of 2.6 qualifies as a Weber Class 3, meaning that that the panel can be used to display Numerics (Class 2) and Alphanumerics (Class 3) data in direct sunlight. Similarly, a display that achieves Weber Class 6 would be recommended to display all of the applications summarized by Weber Class 2 through Weber Class 6.

Table explaining Weber contrast in plain language

Table 1: Weber Class Application Table

 

Engineers and technical staff are routinely asked to select an LCD for use in direct sunlight or high ambient brightness outdoor lighting conditions for military, avionic, industrial, marine and commercial applications. Sunlight readable displays are increasingly necessary for a wide variety of products such as weapons/fire control systems, cockpit displays, air traffic control monitors, portable electronic equipment, digital signage, advertising kiosks, simulators, and much more. Everywhere one goes on-line, consumers find suppliers who claim that their flat panels are sunlight readable and uniquely suited to meet the rigors of these environments. Now, with the enlightenment of Weber Contrast, the average engineer can easily determine whether a display is right for their specific requirement.

Learn more from General Digital’s downloadable PDF document, MIL-STD-3009 Sunlight Simulation and Measurement Test Setup. Or visit our Web site at www.GeneralDigital.com.

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