Today is the day in the United States that Television broadcasts officially switch over from Analog signals to Digital signals.  For those who haven't bought and installed the proper converter box so they can view the new channels (*if* they can get the new channels), an analog "nightlight" will be transmitted essentially informing them to buy the converter box.  http://news.cnet.com/8301-1035_3-10262022-94.html?tag=newsLeadStoriesArea.1?cnn=yes
In Canada, the deadline is August 31, 2011.