Inexpensive LED Video Wall
Stephen Hitchcock and Matt Lathrop
We created a large, modular, LED video display to be used in a variety of activities from concerts, to theatrical productions, to art installations. The wall is made up of 50 4’ x 4’ panels for a total assembled size of 20’ x 40’ and an effective resolution of 200 x 100 pixels.
LED technology has always been expensive, primarily due to the high costs associated with producing batches of quality LEDs to create a uniform image. This video wall was made for roughly 1/10th the cost of a professional product with similar pixel density by using inexpensive LEDs and then imaging our panels with a dSLR to measure relative luminance. Furthermore, we used a color spectrometer to record the gamut, white point, and gamma of the LEDs. With this data we mapped the sRGB color space into the color space of the LED wall allowing us to produce content then display it on the wall while preserving the colors in the final image.
These techniques, combined with the hardware and software design, produced a professional looking video wall for a fraction of the cost of alternatives.
Background
Although LEDs were invented in 1927, when O. V. Lossev of Russia constructed the first LEDs in his paper Luminous Carborundum Detector and Detection Effect and Oscillations with Crystals, it is only within the past 25 years that they have become useful for displays. Many professionally made displays are available today; however, our constrained budget necessitated a search for affordable components adequate to accomplish our goals.
LED Display Technology
The first major LED display was unveiled by James P. Mitchell at 29th International Science and Engineering Exposition in 1978. Though only monochromatic due to the poor performance of blue LEDs at the time, the display was an important both as a prototype and as a demonstration of LED capabilities. Unlike Cathode Ray or Liquid Crystal technologies, LEDs serve as both the source and control on a per pixel level which allows their displays to be both incredibly thin and incredibly large. Furthermore, their vibrant color rendering and low power draw make them a clear candidate for large scale projects, as they are both visible at long ranges and can be reasonably powered with existing infrastructure.
To understand our methodology, it is important to note that in commercial LED display production, individual LEDs are sampled after manufacturing and matched with other, similar performing LEDs. This way, when a large number of LEDs are used in parallel, such as in a display, color rendering and luminance is consistent across the surface. As a result, the manufacturing process is extremely expensive, as the vast majority of LEDs fail to match performance and subsequently cannot be used in a commercial display.
Specifications
The unique qualities of LEDs made them the obvious choice when designing our large scale project. We knew from the outset that our display would consist of fifty 4' x 4' modular panels with a pixel pitch of 2.4 inches. This created a 20 x 20 pixel per panel resolution, allowing all fifty panels to be configured in a single 40' x 20', 200 x 100 pixel display. A commercially available product at this size and resolution would cost in the neighborhood of $100,000 and was therefore well beyond our limited budget of approximately $10,000. Therefore, we also needed to devise a strategy for building a display at 1/10th of normal cost, all while fulfilling our previous requirements.
Methods
In order to meet our specifications, we devised a number of processes and investigations that served the overall processes of sourcing, manufacturing, and controlling our display. Unfortunately, detailing all of these is beyond the scope of this article, and as such, we will be focusing primarily on our methodology for color calibration and control.