Selecting A Display For Digital Signage

Brightness and other factors

A high-brightness display is particularly important if your chosen location is subject to sunlight or bright lighting.  Many consumer-grade displays simply aren't bright enough for the average retail or storefront location and you'll want to look at brighter industrial-grade displays for such locations. 

Contrast ratios and black levels are important but less critical for digital signage than, say, a screen to show movies on.  Typically you will design your content to ensure that your text has very high contrast against the background image or video and that makes the absolute blackness or final contrast less important than a screen for watching movies. 

Viewing Angle

Viewing angle, on the other hand, is much more important for digital signage than for regular TV watching because your audience will often be off-axis and moving around rather than sitting still directly in front of the screen as they would be at home.  You want as wide a viewing angle as possible to ensure that people can read your messages even if they are viewing the screen at an oblique angle.  180 degrees is clearly the theoretical best viewing angle possible since it means anyone in front of the screen can see it but typically you'll find screens claiming around 140 to 160 degrees.  The quoted viewing angle is however somewhat meaningless as most manufacturers use the angle at which the contrast ratio is 10% of the on-axis contrast ... that's barely enough to see let alone to communicate your message clearly.  Most LCDs have a 'realistic' viewing angle for digital signage of around 30-40 degrees from either side of on-axis. 

Viewing angle is normally quoted only for the horizontal direction because screens are typically mounted at eye-level and everyone in the room is at the same level.  But if you are mounting your screen high up, or if you mount it in a 90 degree rotated orientation (portrait instead of landscape) you need to worry about the vertical viewing angle.  Since this number might not be available for your chosen screen the only way to find out is to try it or to ask before purchasing.