fasttruck says it like it is , we were taught a similar jingle about cat eyes except ours was 4 is fine .. blackout was not just for air defense. It also was to be effective against land-based OPFOR weaponry beyond a certain distance.. ya can't hit a target you can't see .. blackout lighting could not be seen by the naked eye out very far, especially in vegetated terrain.
I cannot count on one hand the number of times somebody could get killed during BO-tactical moves in my former armor BN. I think the one that takes the biggest cake was when when our fifteen or so M52's and M54's were about halfway into a 60-minute non-stop move and I get a white BO brake lit up ahead of me. He moves up, white again, moves up, white again .. WTF, over? I get going again only to catch the quick bouncing flash of a BO-drive lite in the corner of my eye way out to my right. I stop just in time to find there are columns of M48 tanks zipping by in front of us in the dust of an unknown crossroads we were apparently at. Apparently one unit CO did not communicate with the other. It was one of those blackest of black nights, nobody could see anything. You couldn't see shapes of the tanks but could hear them over the noise of a truck only when they passed in front of you. I ran back to warn the next truck and told them to send the news down the column. Fun! Oh, and then the time some yahoo read the map wrong and led a small section of trucks into the fire lane (alongside a bunch of target vehicles) on a tank range conducting BO-tactical night fire in the days of barrel-mounted xenon searchlights. I wasn't in on that one but sure heard about it the next morning. They were out doing a BO-tactical refuel to one of the tank companies. I guess you could say they found them!