A Comprehensive Guide to Buying An LED Display
Here we outline some of the key factors you should consider when you first set out to buy an LED screen
Table of Contents:
- LED Display, LCD or Projection?
- Choosing An LED Supplier
- What is an LED?
- The Main Types Of LED
- Custom LED Screen configurations
- LED Pixel Pitch
- Technical LED Specifications
- LED Mounting Solutions
What Size LED Display?
We believe that an LED display should be as big as possible, after all there is no limitation on size and the bigger the display the more of an impact it makes!
What About LED Pixel Pitch?
Some people say that the pixel pitch should reflect how far away the viewer will be standing and this in turn should dictate the pitch size but this is simply not the case. One way to look at this is to consider for instance a standard 55″ television with a HD resolution of 1920 x 1080 pixels and compare this to another 55″ TV, but this time with a 4k resolution of 3840 x 2160 pixels. The 4k resolution looks far more impressive but the physical screen size is exactly the same. We can use this same comparison with LED displays, the bigger the LED screen and the more overall pixels (resolution) the better looking the display. That being said, a very good rule of thumb for newcomers to LED is that for every 1m you stand away from the screen you should have 1mm of pixel pitch. So, for example if you don’t want to see each individual pixel when viewing from 2m you should have a pixel pitch of 2mm and for 3m it should be 3mm and so on.
A Buyer's Guide
LED Display, LCD or Projection?
For most video wall applications LED is fast becoming ing the solution of choice. That’s not to say that there is no longer any place for LCD or projection, for instance if you require a relatively small screen with a high resolution then LCD is the way to go. And likewise if you have no issues with low ambient light levels then sometimes projection can be a viable solution. But with that being said LED is normally a far superior product when it comes to video displays, they have far superior brightness levels, higher contrast levels, and are generally cheaper to run. They do not suffer from burn in like LCD video walls and they do not have the same issues with calibration that sometimes means that one or LCD screens in an array will have a different colour balance and look out of place. That’s not even mentioning the unsightly and distracting bezel lines that are created when LCD screens are joined together!
Choosing An LED Supplier
Always make sure you do your research when choosing an LED display company to carry out your installation. Make sure not to just visit their showroom but to more importantly visit their projects in the field and speak with their clients to see how they rated the experience. You would be shocked to discover the amount of companies that showcase projects on their websites that they had absolutely no involvement with! Another good indicator is to check that the displays you are being shown do not give off a substantial amount of heat, this is a tell tale sign of low quality LED. Ask the supplier to show you the LED screen on full white, does the colour look a little red, yellow or green? Good quality LED display should be able to show a brilliant full white. Always be clear to check the warranty! Most companies offer a return to base warranty which is all well and good when you are made fully aware of this but it can come as quite a shock when 1 month after installation your LED screen is malfunctioning and you are informed that your display is only covered on a return to base warranty! Here at Dynamo we offer a free of charge 1 year service contract on all of our installations meaning that in the unlikely event of any issues we will aim to be on site within 24 hours to rectify the issue.
What is an LED?
<a name=”whatisled”></a>Simply put, an LED or light emitting diode is a semi conductor that emits a light when an electrical current is passed through it. They are made from elements from group three and group five on the periodic table also known as III-V materials. Good examples of these materials include gallium arsenide and gallium phosphide. The first creation of an LED was by Russian scientists in 1927 although LED technology as we know it was first developed just after world war 2 when there was a huge interest in finding materials that could detect light and microwave waves. It was soon realised that these same materials could not only detect but also create light. It wasn’t until the 1970’s that LEDs became commonplace with Hewlett Packard and Texas Instruments among the first to produce items that incorporated LEDs due to a reduction in manufacturing costs. Before this LEDs sometimes had to be suspended in nitrogen to stop them burning out and even then they were extremely inefficient and produced only a small amount of luminance.
The Main Types Of LED
DIP LED or “dual in line package” is probably the kind of LED most people are familiar with. They are the type of LED that is encased in a rounded plastic cover which is coloured a specific shade with metal legs, the positives usually a little longer than the others to distinguish the polarity. The plastic encapsulation can also be designed as a lens which can focus the light in a specific direction, so unlike common light bulbs they do not require reflection to direct light at the right audience. DIP LEDs have a reputation for being the brightest LEDs when it comes to LED displays and are also normally the most reliable LEDs when used in harsh weather environments.
SMD LED or “surface mount devices” are becoming more and more popular due to the fact they use less energy than their DIP predecessors and usually have a longer lifespan in normal working environments. SMD’s are normally mounted directly to the circuit boards and can come in packages of RGB 3 in 1 and these RGB (red, green and blue LEDs) can be combined to make many different colours for essentially one pixel. Good SMD LEDs give off very little heat and do not require as much voltage/current as DIP LEDs. These LEDs can be made in quite small sizes and used in clusters, they have a long life span of around 100 hours. The LEDs themselves come in many different sizes and are usually measured in millimetres with the width and height shown after the SMD so for instance SMD 3528 is one SMD with a measurement of 35mm x 28mm.
COB LED (chip on board) is where multiple LEDs are packaged together and then attached directly to a substrate or driver board. A coating of resin is applied which helps protect the LED display from dust, static, humidity, physical damage and to some degree water. This also means there is a higher level of heat dissipation which in turn results in lower pixel failures and a very reliable product. The fact that the LEDs shine through a resin means that the viewing angles are increased which can be very important in various applications. Brightness and colour uniformity are also improved and with some manufacturers the contrast levels are also higher. Cleaning a conventional LED display can sometimes be difficult but with COB LED technology anybody can simply wipe the surface of any dust/dirt with a cleaning cloth.
MICRO LED is the latest fine pitch LED display technology and allows LED screen manufacturers to create ultra fine pixels pitches the can reach sub 1mm. The technology is inorganic and does not suffer from image retention, burn in and can reach brighter levels while consuming less power. So what is the difference between conventional/mini LED displays and micro LED? Well, its pretty complicated and this is another subject where there seems to be some confusion, the best way to explain the difference is that micro LED doesn’t usually have a substrate where mini LED does. Mini LED has a pixel pitch range of 0.1mm – 1mm and Micro LED ranges from anywhere below 0.1mm.
Okay, so you now know what kind of LED pixel pitch you want to consider and what size you would like your LED video wall but how about controlling it? When it comes to the hardware inside your LED Display the most popular and in our opinion best manufacturer is Novastar. Nowadays nearly all of the top LED display manufacturers adopt their receiver cards inside their screens as they have so many features and are very reliable compared to most of the competition.
There are 2 main types of LED video processors –
Asynchronous LED Processors
These are LED controllers that are connected to an LED display and sent data/content that is then held on a chip within the display and plays without the need for another media player or video input to the screen. It is completely independent from any other source and will usually continue to play until somebody re-connects to change the content. Connection methods vary but can include WIFI, USB, ethernet and some of the latest models even include 3g or 4g network connections.
Synchronous LED Processors
Synchronous LED controllers require a video source that is always connected to the LED screen. This could be a media player, a PC, a video camera or even a computer games console, basically anything with a video source output. The common video sources used for synchronous LED video walls are HDMI, DVI, Display Port and CVBS.
Video scalers are commonly used when the output image from a video source is of a different aspect ratio to that of the LED screen. The video scaler will take this image and then output at the correct size to fit the video wall. Other uses include the ability to splice two or more sources together to create one big image or to use a feature called picture in picture or PIP which enables two or more sources to be broken up into sections and shown on different parts of the LED display with just the press of a button.
Custom LED Screen configurations
One of Dynamo LED’s specialities is the commissioning of custom LED Displays. By custom we mean anything other than the conventional, rectangle LED screens that are popular in ever more applications. With LED it is possible to build in small increments, like brickwork to create an almost bricks and mortar digital installation. Some of the digital installations we have created include shopfronts made entirely of LED modules with returns and soffits, LED towers that have right angles and even double decker buses and hot air balloons with LED screens attached.
Indoor LED Displays
Indoor LED screens are generally smaller than their outdoor counterparts but usually have a smaller pixel pitch due to the fact they are viewed from a closer distance. That’s not to say that they have any limitations on size as they can also be made to any size required. Over the last few years developments in the technology mean that indoor LED displays can be used in far more applications and they are now used as replacements for conventional TV’s.
Outdoor LED Displays
Outdoor LED displays are most often used as advertising billboards but can also be seen in applications such as LED scoreboards or pitch side perimeter advertising. They need special protection from weather elements and this level of protection is referred to as the IP rating. Outdoor LED screens also have a shade which is situated above each individual pixel to stop direct sunlight from shining onto the screen and diluting the light that is emitted.
LED Pixel Pitch
LED Pixel pitch is the distance between each pixel within an LED screen, a pixel pitch of 1mm means the distance from one pixel to the next is 1mm. Some displays have a horizontal pitch and also a vertical pitch so the vertical could be 5mm while the horizontal could be 10mm. The closer the pixel pitch the higher the resolution and as a result the higher the cost of the LED display. Some manufacturers offer solutions called virtual pixel pitch, this is not something we would recommend as it basically adds another red, green, blue or even white LED into the segment which results in a loss of contrast due less black space between the LEDs. Another con to virtual pixel displays is the fact that often manufacturers will use an additional LED which uses more power and so the brightness settings will be set lower, over time the other colours will see more degradation than the lower brightness LED and the screen will require calibration to equal this out.
LED screen brightness is normally measured in nits per m2 and can vary depending on pixel pitch and wether the LED display will be used indoor or outdoor. Indoor LED displays have a brightness range of 500 nits to 3,000 nits whereas outdoor LED screens are normally rated from 4,000 nits anywhere up to 12,000 nits or more. LED brightness can be one of the factors to consider when buying an LED screen, for instance if an LED screen is to be situated in a bright window a standard indoor brightness display will not be suitable when direct sunlight hits the display.
LED Display Resolution
Resolution is determined by the amount of pixels within an LED display and choosing the required resolution often depends on what content is going to be shown as well as the size of the display. For instance, if you are installing an LED screen into a control room environment where intricate content will be shown then a high resolution will be needed but sometimes a low resolution is acceptable. An example of this could be roadside signs that will show traffic information such as stop signs or scoreboards at sports stadiums.
Technical LED Specifications
Reading the specifications sheet for an LED display can sometimes be a very daunting task. With segments such as scan rate, refresh rate, pixel density etc things can get a little confusing. To help you understand what each of these factors mean we have put together the following to help buyers understand the terms used on most technical sheets.
As we covered earlier the pixel pitch is the distance between each individual pixel. The closer the pixels the higher the resolution and the more clear the picture will appear. Currently the lowest pixel pitch is around 0.6mm although these displays are not currently live in the field. Outdoor LED displays vary and can even exceed 100mm.
Pixel density is the amount of pixels in any given area. A pixel is normally made up of a red, green and blue LED in a full colour solution but can also be one individual pixel in mono colour for instance. pixel density is usually measure in pixels per meter square so for instance a 2.5mm pixel pitch will have a pixel density of 400 x 400 and be 160,000 per m2.
LED Refresh Rate
LED refresh rate is the amount of times the display changes frames or in other words the image that is displayed. Most LED displays are above 240hz but in configuration settings we can adjust these numbers depending on how the display will be used. to do this we can sacrifice other settings such as colour range. For some settings, however, such as when the display will be filmed with a camera it is essential to adopt a high refresh rate, we usually recommend at least 1920hz for these scenarios.
LED Display Brightness
LED Display brightness is usually measured in nits over a meter squared (cd/m2) and can vary enormously depending on the type of LED used and whether it will be used for indoor or outdoor applications. As a rule of thumb, indoor LED displays will have a brightness of 500 nits to 3,000 nits and outdoor LED displays will start at around 4,000 and depending on the type of display can reach over 12,000.
This is how the LED is packaged, the size of the LED and also the kind such as DIP, SMD or COB. An example would be SMD 2020 1R 1G 1B which means the spec is for a surface mount device, 20mm x 20mm pixel containing 1 red, 1 green and 1 blue LED.
LED Display Contrast
One of the biggest benefits of LED displays is the extremely high levels of contrast that are available. Contrast is the difference between the white and black image that screen is able to show. The larger the difference in contrast the better the picture quality, especially when watching darker content on the screen.
LED Viewing Angle
LED display viewing angle is far superior to nearly all of its competition due to the fact that the light creating the image emits directly off of the surface as opposed to sting through it or onto it like other solutions such as LCD or projection. Most LED screens have a viewing angle of at least 100º but vary both horizontally and vertically and can reach up to 170º.
LED Scan Rate
The scan rate is how many lines of the LED module the chip will change at any given time. The scan rate will usually be considered alongside the refresh rate and we usually specify our LED displays scan rate depending on their environments. For instance, in a hot outdoor location we prefer to use a lower scan rate so that the LED chips are not working so hard and have a longer life time.
LED Grey Scale
LED greyscale is basically what is sounds like, it is the amount of levels, on a scale that an LED display can show between shades of colour. There are 256 levels of intensity and so the highest possible greyscale is calculated at 24 bits whereas the lowest amount would be 1 bit or 2 colours such as black and white.
LED Life Span
LED life span indicates the the expected lifetime of usage for an LED Display. This is usually 100,000 hours of use or 11 and a half years which is quite a significant amount of time. Even when there are failures within an LED display the modular nature means that all is required to fix the display is to simply replace the component that has failed such as a receiver card or PSU.
LED Mounting Solutions
LED screens can be mounted in various ways. Some screens can be fixed directly to walls whereas some displays require that special frames are built to accommodate the LED cabinets. Many companies are now starting to produce mounting solutions that fit multiple manufacturers LED cabinets. One of the most important things to consider when selecting an LED mounting solution is how to maintenance will be carried out if necessary. Most LED cabinets these days allow for both front and back maintenance of all the components.
LED screens are usually built in batches which means the LEDs are supplied calibrated from the factory and ensures that the levels of brightness, contrast and the colours of the LEDs are all equal. Calibration using the kind of expensive camera equipment that Dynamo LED have invested in can also give that extra bit of quality which is why all of our screens have that added bit of “Wow Factor”.