LED it be! Large outdoor screen types.
David Thilwind is the International Marketing Manager for Lighthouse Technologies, a manufacturer solely dedicated to developing and producing LED screens for staging, rental, and outdoor productions. The article was published in web journal tfwm.com.
It has been the case in the past, and remains the prevailing assumption that LED screens are only for baseball stadiums, and beyond the means of all but the wealthiest of organizations. Maybe this was the case 4 or 5 years ago, but not anymore. With falling component prices and increased design efficiency, the LED screen is very much within the realms of possibility for all but the most humble of budgets.
The unique advantages that LED screens are now offering are drawing the crowds back to venues that have been losing audiences in huge numbers. This is the driving factor, and key point. Is your event an attention grabber, or sleep inducer? In the following article, we'll explain some of the terminology, along with a few good rules of thumb, which should help you make an informed choice about LED screens.
Defining large screen video displays
The true purpose and reason for having a large-format video display is to show full-color moving images to large crowds. In the past, successfully building very large or very bright video displays has been difficult, as the only real solution, projection, suffers from a lack of brightness and contrast in high brightness environments.
If you think back, a very famous consumer electronics company offered the first real alternative using CRT-based solutions. They were heavy and power hungry and suffered limitations on the resolution they could achieve, and all this for a king's ransom.
The relatively recent (since 1996 onwards) full-color LED video display technology has at last made large, bright video displays practical and affordable. Generally though, large displays are used in locations where a group of people must be able to see the display, such as sports arenas, pop concerts and shopping malls.
These displays are generally large (from 1.5 m to 30 m wide or bigger) and naturally very bright - to overcome high ambient light such as television lighting or direct sunlight. Let us look at the major large-screen display technologies in some detail.
Rear projection & video cubes
The limitation of video projectors is brightness. Even with the latest DLP, or LCOS type of projectors, ideally the environment needs to be low-brightness to achieve an acceptable viewing experience. High gain projection screens can help in low ambient brightness environments, but in most naturally lit, or bright artificially lit environments, a projector may not be the best alternative.
Rear projection and video cube's screens
A video-wall cube system, is made up of a small projector, with the image bounced off an internal mirror to appear on the rear of the video cube screen. This method keeps the profile of the units to a minimum, and allows them to be used as in-store large displays. The image is chopped up into parts by a special video scaler, and distributed to the cube projectors.
A thin, but visible dividing line, can be seen between the cubes. These displays also have low brightness (average only about 400 to 600 nits). It is very hard to adjust each cube to exactly the same color balance, and even harder to keep them this way.
CRT technology
This was the original big full color video screen system, and due to the costs from a difficulty in the manufacturing process, few companies ever made CRT. Now they are virtually extinct. The best known examples of CRT screens were made by Mitsubishi (Diamond Vision), Panasonic (Astro Vision), and Sony (JumboTron).
Video CRT screen JumboTron
The image from the video feed is divided up into a number of dots called pixels. Each pixel is made up of at least three tiny CRT's (cathode ray tubes) - one red, one green, and one blue. By varying the brightness of each of these, any color can be created.
Each of these CRT's is like a tiny television picture tube, except that it is producing only the intensity of one picture dot, and the entire picture is made up of hundreds of thousands of CRT's, rather than one. The end result is a large, bright video image. The horizontal viewing angles on these systems were poor in comparison to current LED screens, not to mention the fact that were very power hungry.
CRTs and CRT's modules Diamond Vision by Mitsubishi
Lamp screens
Inside lamp screen
In lamp screens, similar to video cubes, the video image consisted of pixels. Pixels were made of separate incandescent lamps covered with color filters of red, green and blue. Lamp screens boasted high brightness and contrast. The downside was low resolution and high energy consumption. Our magazine wrote a lot about this technology a few years ago.
LED technology
In the late 1990's, with the discovery of the stable and bright blue LED, video screen technology using LEDs was born. These LED video screens rapidly advanced beyond CRT's for resolution and brightness, for significantly less cost.
Add this to the fact that LED displays consume far less power, and are considerably lighter than their CRT-based counterparts, and they occupy less volume (they are less than half as deep). All of these aspects made them very attractive in the AV rental and fixed installation market. CRT technology had been limited to three principal vendors primarily due to the complexity of the manufacturing process.
LED technology is much more accessible - resulting in many more manufacturers (one industry report cites as many as 50 manufacturers although there may be this many in China alone!). An unfortunate side effect of this diverse manufacturing base is the proliferation of some poorly designed product and some short-term manufacturers who may sell only a few systems before vanishing.
One key to choosing an LED screen is to select a manufacturer with a long track in full color LED screen, and who is committed to the industry. If you wind up owning an unsupported “orphan” product, you can't say you weren't warned!
In particular, beware of a new LED video product from a company that has only previously done animated LED signs, and has no video experience. Video demands very high speed processing, currently beyond the capabilities of some PC based processor, and the results are often very disappointing.
