To complicate matters, a very different method must be used when measuring the contrast ratio of an indoor display versus an outdoor display. Angle of view is another important consideration - can every seat in the house see the display equally well. The manufacturer quotes the display's viewing angle and, again, it is not always clear how this is measured. Unfortunately, LED displays have a problem that is unique to this technology called 'shouldering'. There is a colour shift caused by one LED blocking the view of another LED at extreme angles.
Life expectancy is another interesting issue.
Quoted life figures for the LED's range from 20,000 to 100,000 hours. These figures are clearly only meaningful if they are determined at the actual drive current that will be used under real display conditions - certainly at the drive levels used to produce the brightness measurement. Once you have narrowed the field, arrange to see exactly the product you are considering. I was not prepared to recommend that my client become a guinea pig for the first commercial model of a manufacturer's jumbo video screen. If you find yourself unavoidably in this situation, be sure to contract-in, a free upgrade to whatever changes may be made within, say, six months, or the next four screens sold.