Cut 8 small holes with scissors above the brim on the front side of an old baseball cap. Make two rows of four lights, stacked on top of one another. Poke the scissors through the fabric, and make a hole no larger than the diameter of the LED lights.
Solder 8 inch long lead wires onto each of the IR LED lights. Make sure you use electrical solder, otherwise the connection will not conduct electricity. The metal leads on the lights are labeled with a positive and negative sign. Connect one color (red) to all the positive leads, and another color (green or black) to all the negative leads using two colors of bell wire.
Poke each of the IR LEDs through the holes in the front of the cap, and then glue them in place with the adhesive GOOP.
Strip 1/2 inch of the insulation off the ends of the wires attached to the LEDs after the glue sets, using wire cutters. Twist all the wires which are the same color together, and solder the wire bundles to the terminals on a 9V battery harness. Connect the red wires to the positive terminal, and connect the black or green wires to the negative lead on the battery harness.
Connect a new 9V battery to the harness after the solder cools, and then tuck the battery into the hat, or tape the battery to the top of the cap with a bit of duct tape. The IR LEDs are now lit, even though they are invisible to the naked eye.
Turn on the camera feature of a cell phone or smart phone. Point the phone at the hat. By using the camera as the “goggles,” you will see the light emitted from the IR LEDs. In a dark room, the light emitted from the LEDs on the hat will be visible in the viewfinder of the cell phone camera. Children can play in a dark basement, or outside after sunset, and use the camera and hat together to play hide and seek, or explore the darkened neighborhood via the homemade night vision system.