Simple Halloween Trick - Invisible Glowing Eyes

Want to confuse or impress your Halloween visitors this year? This 'glowing eyes' ghost proves that you can't always believe your eyes.

If you build it as shown below and apply power - you won't see anything happen, but looking at it through a phone or camera will reveal ghostly glowing eyes. This is because phone cameras are sensitive to infra-red light that is not visible to the naked eye.

1. A sheet of paper and a printer - or impressive drawing skills.
2. A cardboard backing - an old double-walled box should be fine, it's just to add rigidity to the paper.
3. A couple of infrared LEDs. You can harvest these from old remote controls.
4. A couple of resistors - anything around 47-1000 ohms should be OK, depending on how bright you want it, and how bright your LEDs are.
5. An AA or AAA dual battery box.
6. A couple of short lengths of wire.
7. A glue gun to anchor the LEDs in place.
8. A glue stick or double sided tape to paste the drawing onto the cardboard backing.
9. Wire cutters to trim the LEDs and strip the wires.
10. A soldering iron and solder - you could also use crocodile clip wires for a younger audience, or to make it reusable.

You need a forward-facing ghost or ghoul with big prominent eyes, try to scale the picture so that the eyes are about the same size as your LEDs. I printed a couple on one page in case I made a mess on the first attempt.

Pretty self-explanatory. Use the glue stick or double sided tape to paste the image flat onto the backing cardboard, then cut it out.

Stab it in the eyes using a pencil or other sharp implement, try to make a nice even and round hole just large enough for the LEDs to fit through.

Poke the LEDs through the holes, and apply hot glue to the back, allowing the legs of the LEDs to stick through.

Solder the resistors on to each LED negative lead (generally the shorter of the two leads, when they're new). Salvaged LEDs may have already had the leads trimmed, so you will need to test these.

Hot-glue your battery box onto the back of the cardboard, and wire it up to the LEDs as shown. By careful placement of the battery box it will also double up as a stand to keep it upright.

Insert the two batteries and flip it over. Use your phone camera to check they both light up.