NASDAQ Quick Fact Tens of millions of dollars have been spent on the NASDAQ sign; just the electricity for the sign costs more than $1,000 per day.

When you think about Times Square in New York City, probably one of the first things you imagine are the megascreen billboards there. The NASDAQ MarketSite Tower sign is the biggest one of all. Let's explore it to find out how these megascreens work. First we'll start with the smallest part of the sign – the tiny light bulbs. Each tiny, colored bulb is a single light emitting diode, or LED. You see these little lights everywhere – like on your DVD player for example. LEDs have three big advantages when it comes to making a gigantic TV screen. First, they are bright. Second, they are efficient, meaning that they turn most of the electricity they receive into light. Third, they last a long time. A typical LED might last 100,000 hours before it burns out.

The NASDAQ sign during the day

On any large LED sign like this, you use clusters of LEDs to make one pixel. For example, a small sign uses a red LED, a green LED and a blue LED to make one pixel. By changing the brightness of the three LEDs, you can create any color in the rainbow. Turn all three LEDs off, and that part of the sign will be black. Turn them all on at full brightness, and that part of the sign will be white. And you can create any color in between.

In a big sign like the NASDAQ MarketSite Tower, you need even more LEDs in each pixel because the sign is so large. This sign uses two red LEDs, three blue LEDs and three green LEDs to make a single pixel. Since the sign has 1,800 by 1,200 pixels that means that there are about 17 million LEDs in the sign. These LEDs are wired onto boards called tiles. A tile has 256 pixels, arranged in a 16 x 16 grid. A tile also has its own computer to control the LEDs on the tile. The NASDAQ sign has 9,000 of these tiles.

The NASDAQ sign at night

The tile needs data to tell it how to light up the 256 pixels. This data comes from a main control computer that knows how the whole screen should look. The data for the tile contains an intensity level for the red, green and blue LEDs for each of the pixels. In other words, 30 times each second, all 256 pixels on the tile need to get intensity information. The computer 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 along the data from the main computer from tile to tile.

NASDAQ sign LED pixel

The other 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. If you multiply 9,000 tiles by 60 watts, you can see that this sign needs 540,000 watts - enough to power several hundred houses. The problem is, all those tiles and power supplies generate a lot of heat. To handle all this heat, 12 large air-conditioning compressors chill a glycol solution that circulates behind the sign. The air conditioners can use about as much power as the sign itself.