The primary intention of this section is to inform the potential buyer of the main factors to consider when choosing a video screen for purchase. If you base your decision on these recommendations, you can be guaranteed that your decision will be 100% correct. The specific model of the video screen you purchase should primarily be determined by the location of its installation and the conditions of its review. This section will equip you with an in-depth knowledge of LED screens so you can discuss your options with experts authoritatively.
Things to do Before Buying a Video Screen:
- Estimate the size and location of your screen.
- Decide what kind of media you would primarily like to display on the screen.
- Decide the pixel pitch, i.e., the screen resolution.
- Decide the real and virtual screen resolution.
- Make a decision regarding the screen brightness and viewing angles.
- Consider the minimum and maximum distance of viewing.
- How many and what types of video sources will you use?
- Will the screen be installed permanently or do you need it to be portable?
- Choose a screen control system.
Video Screen Size and Location
The process of choosing a video screen model (its size and resolution) is extremely important. The model you chose won’t just determine the cost of the entire project but also the prospect of selling advertising time on the screen. In fact, an incorrectly selected video screen could potentially worsen your sale of advertising time, regardless of how good the screen installation site might be. If you install a 3 x 4 meters video screen for a viewing distance of 400 to 600 meters, approximately 200 to 300 meters of effective viewing will simply be lost.
Additional recommendations for determining the parameters and linear dimensions of the video screen can be found in the section of our website called “Effective Viewing Distance”.
Type of Information Displayed on the Video Screen
Determining the type of media or information displayed on the video screen will allow the manufacturer/supplier to assess the necessary steps between the pixels of the LED screen and its characteristics. When you plan the budget for a video screen — especially an LED screen — you need to consider the content displayed on the screen or your purchase might prove to be disastrous.
Pixel Pitch Selection
The choice of the pixel pitch and the video screen resolution dictates the physical limitations of the video screen size, viewing distance, viewing angles, and, of course, the budget. The cost of the screen is determined by its resolution and area.
In order to produce high-quality videos on a large video screen, you need to purchase the screen with the highest resolution possible under your budget. The screen resolution is defined as the total number of vertical and horizontal pixels (the dots that form the whole image).
If you plan to display live video broadcasting, the video signal played on the video screen will have a resolution of approximately 486 (NTSC) and 576 (PAL-SEKAM) vertical lines and approximately 240-720 horizontal lines (subjective upon the source quality). To reproduce these signals without compromising resolution, you need a minimum video resolution of approximately 648x486 for NTSC or 768x576 for PAL-SEKAM).
If your screen’s pixels are less than those in the video broadcast’s signal source, the images reproduced by the screen will have a lower resolution than the original source. However, if the video screen is well-constructed, it can reproduce a sharp visual. Screens with a resolution of 1/2 VGA resolution (320 x 240 pixels) are suitable for this purpose.
Real and Virtual Screen Resolution Video
You should pay especially close attention to this key point when choosing a screen model and manufacturer. For more information about the real and virtual resolution of the LED screen, please refer to the section entitled "Virtual Pixel".
Brightness and Viewing Angles
The unit of measurement of the brightness of the LED screen is nit (cd / m2). The higher the value, the higher the brightness of the video screen. The brightness for internal screens should be no more than 1,500 - 2,000 nits. For external screens, the brightness should range from 3,500 nits (for screens without direct exposure to the sun) to 5,000 nits or more (when the screen is directly exposed to the sun). Brightness is measured at a normal angle to the screen. The color temperature of a video screen should typically be 5000°K for internal screens and 6500°K for outdoor screens.
The viewing angle is usually determined by the point where the screen’s brightness is 50% of the maximum. You should notice a change in brightness as you walk along the length of the screen. LED screens have a problem unique to this technology, called “shoulder obstruction”, i.e., when the color change occurs because one LED blocks (obstructs) another LED at critical viewing angles.
Viewing angles should include color changes. If a significant color change occurs before the brightness drops to 50%, then that is considered as the viewing angle. The addition of visors between pixels or rows of LEDs reduces the illumination of the video screen by other light sources, thereby increasing the contrast. This method also reduces the vertical viewing angle, but that is not usually a problem for most LED video screen applications.
Let’s consider roof-mounted screens as an example. In this case, a wide viewing angle is not important. What’s more important is the orientation of the video screen to the priority flow of the audience. That is why video screens with viewing angles of 60 degrees — instead of 120 degrees — facilitate more efficient use of the LEDs of the video screen and its brightness.
If video screen manufacturers use high currents to control LEDs, they can indicate screen brightness in excess of 7,000 nits, even though it is physically impossible to get a brightness higher than 5,000 nits for LED screens with a pixel pitch of 25 mm and higher. However, the problem with high brightness is that high currents of control of LEDs can also lead to the screen’s quicker degradation. As such, the screen’s uniformity of brightness and colors can quickly change. The lifespan of a typical LED is in the range of 20,000 to 100,000 hours.
These screen brightness figures are only valid if they are determined at the actual control currents of the LEDs that will be used in the actual display conditions, and when measuring the brightness of the actual screen. While evaluating a large-format video screen, you should always check with the manufacturer or supplier.
Color mixing distance, minimum viewing distance, and maximum viewing distance.
Color Mixing Distance:
When the viewing pixels are near, RGB LEDs (red, green, blue) appear as independent points. The distance from the LED screen at which the three separate colors combine into one color is known as the “color mixing distance”.
The ability to better mix colors allows images to appear clear and sharp at nearer distances as well, making it vital for internal video screens. For outdoor screens with conventional “lamp” type LEDs, the color mixing distance can be calculated using the formula: Pixel Pitch x 500.
For example, for a video screen with a pixel pitch of 19 mm, the color mixing distance is 19 mm x 500 = 9.5 m.
For internal screens with SMD LEDs (three LEDs in one package), this number is 250 because the LEDs are close to each other. Therefore, for an internal LED screen with a pixel pitch of 10 mm, this distance is 2.5 m. This distance is often mistakenly referred to as the minimum viewing distance.
Minimum Viewing Distance:
This value can be calculated as Pixel Pitch x 750-1000. At this distance, a smooth image is observed. Closer inspection of the video will lead to a "decay" of the image into separate points (pixels). For example, for a video screen with a pixel pitch of 19 mm, the minimum viewing distance is 19 mm x 1000 = 19 m.
Maximum Viewing Distance:
The formula to calculate the maximum viewing distance is generally Screen Height x 20-30. For example, for a video screen with a height of 4.56 meters, the distance will be 4.56 m x 30 = 137 m.
The Choice of Control System LED Screen
When choosing a video screen, pay special attention to the screen control system. It is usually a control computer under the Windows operating system. However, if you plan to connect your screen to the internet to remotely control the schedule for displaying video clips and upload them to the hard disk of the control computer or are going to connect your screen to a network of LED screens with control from a single center, it is preferable to choose a control system running under Unix, Linux, or other similar operating systems. This will increase the stability of the control system and protect it from unauthorized access and attacks.