Here's a fun little thing to try. Turn on a TV in a room with the volume off and leave the door open. Next, stand down the hall and watch the flicker rates. Also notice the hue changes. Sometimes flickers when red and solid blue with no flicker and sometimes blue hue with flicker and solid red. Now have someone in the room watching the TV and after a while ask them if they noticed it. Then change positions so it becomes understood by both what is happening without direct perception. Let the learning begin...