They have revolutionised the super-large display world, replacing billboards and giant signs with their eye-catching impact. They’ve made the futureworld vision of Blade Runner into an everyday reality (set in 2019, by the way, if you’re not already feeling old!).
Direct view LED displays sit at the top end of the ‘displays continuum’ where there’s an overlapping thread of technologies: from tiny 2” LCD screens on petrol pump handles; to large format LED-illuminated LCD flat panel displays which reach their expensive peak around the 98” size; then projection (coupled with ALR screens for displays’ purposes) which can go a any size (when ambient light is controlled/dark) - and then finally to these direct view LED screens. In the UK, the Tottenham Hotspurs’ new stadium in London is a prime example of this technology at its best.
There is a world of confusion here, with dozens and dozens of competing manufacturers. It’s important to know that product differentiators are primarily driven by the quality grading of the individual LEDs that make up the displays, followed by quality of panel manufacture and mechanicals and then image processing. This creates the sometimes baffling price differences for systems notionally of the same size and resolution.
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To calculate image size, multiply the LED ‘pitch’ (size) by the image resolution. Example: an HD display 1.2mm LED pitch has 1920 x 1.2mm LEDs and therefore creates an image of 2.304m width; then 1080 x 1.2mm LEDs creates the 1.296m image height. You can approach this the other way so, for example, a 4m x 2.25m that needs 1920 x 1080 HD pixel resolution will therefore need a pixel resolution close to 2.08mm (4000 ÷ 1080 = 2.08).
Direct view LED screens’ brightness (up to and over 5,000 nit [candelas per square metre]) are both their strength and weakness. Signage and advertising, for example, can benefit from such punch and impact where dwell and viewing time is brief and viewers can choose to look away.
Such brightness must be avoided for presentation and teaching - in fact any situation where viewers need to engage fully with the content. (This is typically the Basic Decision Making viewing category within the PISCR/ISCR and DISCAS standards.) Such applications leave viewers little choice but to stare continuously at the screen. The critical factor here is to have seen, tested and confirmed that the proposed product’s image brightness (luminance) can be wound back to the point where it won’t create eye strain - and its colour and image quality rendition is not compromised in the process. It’s all very well for the brochure to claim a direct view LED screen delivers, say, 3000 nit (candela per square metre [cd/m2]) when this would cause severe optical fatigue and what’s actually needed might be less than 300 nit!
See the Projection vs LED comparison article for more information about choosing the right screen for you.