Choosing a Display for Digital Signage


Display Technology


For the purposes of this article, we’ll assume an indoor 2D application. Let’s assume you’ve opted for a large flat panel display (rather that a projector), so the first question is what technology? There are three main contenders:


  • LCD (cold cathode ray tube back lighting)

  • LED (either edge-lit or back-lit LCD)

  • Plasma


OLED will be a fourth choice towards the end of 2012 (for those with deep pockets). There are a lot of articles on the differences between these technologies, so we’ll just concentrate on the key factors that should be considered for digital signage. For comparison, I chose a current commercial (more on this later) LCD, LED and Plasma from Samsung.


The three main factors to consider are:


  • Brightness

  • Contrast ratio

  • Viewing angle

  • Power consumption


Brightness


As many digital displays will be installed in high-ambient light environments the brighter they are the better. Their job is to stand out and get the message across.


Contrast Ratio


True contrast ratio (i.e. one that matters) is calculated by dividing the brightness of peak white by the brightness of black on a calibrated display. Unfortunately, most manufacturers now quote “dynamic contrast ratio” and many fail to mention “dynamic”. Dynamic contrast ratio is marketing fluff. Instead of measuring the darkness of the screen when it is on (i.e. the backlight is on), the manufacturers measure the black level in standby mode. Unfortunately, in the world of marketing, when one vendor quotes higher (artificial) numbers, the rest have to follow or risk losing sales. A higher contrast ratio is achieved by having brighter whites and darker blacks. Today, Plasma wins on the darker black front, but OLED will surpass even that.


For displays in high ambient light environments, contrast ratio can pretty much be ignored (as long as the brightness is adequate). In these kinds of environment, the internal reflections off the screen are much brighter than the screens internal black. Remember, the black cannot get any blacker than the screen is when off. I have a Pioneer Kuro Plasma, but in the daytime, when the display is off, the screen is a definite gray, rather than black. At night, when I’m watching a movie with the lights dimmed, it’s impossible to see the transition from the dark areas of the screen to the bezel.


Viewing Angle


Unfortunately the specifications are no help here. Most LCD/LED displays have a quoted viewing angle of 178-degrees. The problem is, that doesn’t tell the reader how good the picture quality is at that angle. To give you an example, I have two laptops: a MacBook Pro 17” with HD monitor and an HP Envy 17. When I move off to an axis of angle of 45-degrees, the Mac looks perfect. When I do the same on the HP, the colors are washed out it looks terrible. Generally speaking, displays using in-plane switching (IPS) are the best for off-angle viewing. (This is the same technology used in tablets like the iPad and Kindle Fire.). So if the display will be mounted where viewers will see it from a sharp angle IPS is probably the best choice for LCD/LED displays.


Plasmas generally have a quoted viewing angle of around 160-degrees. That said, I can look my Kuro at as close to 180-degrees as I can get and it still looks perfect. My best advice would be to look before you buy (which is harder with a commercial model) or consult with an experienced integrator/VAR.


Power Consumption


The utility cost to run digital signage can quickly add up. A 55” LCD/LED typically consumes around 200w, whereas plasma will typically consume around 500w. For a single screen, this results in a difference of almost $300/year (assuming 11-cents/kwh and running 24/7/365). Clearly, for multi-screen installations, this can be a significant extra cost.


Commercial vs. Consumer


Although it’s tempting to buy an inexpensive consumer-grade display for under $1,000, it’s not a good idea. Put simply, commercial displays are not built for the rigors of longer run times and, most importantly, will typically only carry a 90-day warranty for commercial use. Below is a comparison from Samsung of the difference between Consumer and Commercial displays. We’ll take a look at some of these in detail.





















 


 HD TV


HD Display


Suggested Use


Consumer


Commercial


Tuner


Built in


Built in Options/External Options for LCD’s


Suggested daily usage


Up to 8 hours


Up to 16 hours Commercial Grade


Up to 24 hours Industrial Grade


Electronics/Power Supply


Light Duty


Heavy Duty – Larger Capacitors


Image Retention/Burn-in Reducer


No LCD/Yes Plasma


Yes/Yes – Enhanced


Built in Fans for Longevity


No


Yes – Adjustable Speeds


Heat Sync Technology


No


Yes


Temperature Controls


No


Yes – Auto Panel Shut Down


IR Remote/Button Lockout


No


Yes


Panel Position


Landscape


Landscape and Portrait


Thin Bezel


No


40mm, 20mm, 11mm, 3.7mm


Connections


Designed for TV’s


Display Port, RS-232, Video Wall, RJ45


Video Wall


No


Yes – built in Video Wall Processor


Digital Signage Option


No


Yes – built in PC/Software Option


Panel Brightness


Typical 450 Nits


450 Nits, 700 Nits, 1500 Nits


Panel Glare


High Gloss – High Glare


Flat Black – Very Low Glare


Off Timer


Controlled by Remote


Programmable


Warranty


1 Year Residential


3 Months Commercial


3 Year ON SITE


Warranty


This is probably the single biggest issue for a single-screen (i.e. non-video wall) display. Virtually all vendors have the same stance as Samsung. This should be a good indication whether the display is fit for purpose. If the manufacturer is willing to lay bets on a 90-day lifetime, then you shouldn’t either. A typical commercial display will include a 3-year on-site warranty. This is critical in applications such as menu boards. It’s OK if a flight arrival status board happens to fail, there are a lot of ways to find out about flights, but if the menu can’t be displayed, you can’t sell product. There’s no way you can afford to wait for a 3-4 week repair turnaround under the included return to base warranty.


Aesthetics


Consumer TV’s typically have wider bezels that accommodated speakers and user controls. Below is an example of a current Samsung consumer LCD. For digital signage this is poorly suited for many reasons:


  • Bezel is too thick

  • Bezel is not symmetrical (wider at bottom)

  • Vendor branding is too prominent

  • Visible user controls/status LED’s



This soon becomes obvious when mounted in portrait mode



For video wall applications, an ultra-thin bezel is mandatory. Modern commercial displays have bezels under 2.5mm. These are creeping into high end consumer models now, but typically at the premium price points.



Electronics


Ignoring the aesthetics, consumer displays should never be mounted in portrait mode. Consumer displays are designed for landscape operation only. A commercial display is designed for either orientation and the heat dissipation mechanism is design for this. They can also withstand more extreme temperature than one designed for a residential living room.


Power supplies, capacitors and fans are all heavy duty for the rigors of 24/7/365 operation.


Consumer displays have limited support for PC resolutions. Commercial displays have to support inputs from a much wider array of input frequencies and resolutions, so tend to have much better internal scalers (or software scaling algorithms.)


Picture


The grayscale on a commercial display is much more linear than that of a consumer display, which tends to be skewed ore towards the bright end of the spectrum to suit broadcast standards (such as NTSC, Rec.709, etc.) The coatings on the glass are also different on commercial displays, which can have a significant effect on the picture under many lighting conditions/viewing angles.


All commercial displays have advance algorithms to prevent burn-in or image retention (which affects LCD as well as Plasma)


Connectivity


It seems that modern consumer TV’s have more inputs than you’d ever need, but commercial models have more input types and more connectivity: most notably RS232 and video loop-through. RS232 allows the screen to be controlled from external devices (typically a digital signage player, or a PC). Loop through allows multiple units to display the same source with no loss of quality. In conjunction with software, it can also be used for video wall applications.


Security


Every consumer display is designed for easy to access to user controls. For commercial displays, the opposite is required. User controls are always hidden and usually have security controls, including the disable user controls and the IR receiver.  Commercial displays are usually powered on or off automatically using VESA power control or via RS232/IP communications.


Conclusion


There are some cases where you can get away with a consumer displays. A company I worked for exhibited at a 3-day expo every year. We purchased three 46” consumer displays for $600/each and they worked great. We used them for 8 hours/day for three days and kept them for two years. (The only reason we got rid of them was that they looked too dated after two years.) For occasional/non-critical use, you could get by with a consumer model. For commercial applications much longer run times are required and the range of connectivity and security is normally higher than consumer displays offer.


Commercial displays are not that much more expensive. A client of mine just bought a Samsung professional 46” LCD for under $1,500. Above all, the 3-year warranty and fitness for purpose should be the overriding factor.

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