The goal of a tile on the NASDAQ sign is to manage the 16x16 pixels on the surface of the tile. In order to do its thing, a tile has two requirements. First, it needs data to tell it how to light up the 256 pixels. The data contains an intensity level for the red, green and blue for each of the pixels. In other words, 30 times each second, all 256 pixels on the tile need to get intensity information. The controller on the tile decodes this information and drives transistors that send electricity to the LEDs. The tiles all chain together, one to the next, and pass the data from tile to tile.
The second thing a tile needs is power. Each tile uses about 60 watts when all the LEDs are lit at full intensity. The power comes from a set of 700 power supplies that are housed behind the sign.
The entire sign contains about 1,800x1,200 pixels, or roughly 9,000 tiles. That's about the same number of pixels on an HDTV screen (although, on an HDTV screen, the pixels are arranged as 1,920x1,080 pixels). Holding those tiles requires a huge framework of steel that is bolted to the building. In addition, there is a series of catwalks and ladders that let maintenance personnel access and repair the sign, as needed.
The transistors and chips on the tiles all produce heat. So do the 700 power supplies. There's also solar heating when the sun hits the sign during the day. To handle all this heat, 12 large air-conditioning compressors chill a glycol solution that circulates behind the sign.
If those air conditioners were ever to fail while the sign was running, it would be a big problem, especially if someone was working on the catwalks. It's estimated that it would only take a few minutes for the heat to build to 200 degrees or more behind the sign. Anyone working in the tower would bake to death.