You aren’t’ likely to see a lot of geocaches that use infra-red clues. Caches that use infra-red (IR) light are harder to create and require special equipment to find them. With UV enabled caches your eyes can pick up the interaction between the UV light source and the UV reactive material. An IR cache needs two components, an infra-red light source and an infra-red capable camera. Any remote control that requires line-of-sight to your TV uses an infra-red LED. You can either take apart an old remote control or you can buy IR LEDs for about 50 cents each. We opted to buy them for our Lunar Lander BFL Boot Camp cache.
Now that we have an IR light source we need to figure out what to do about a camera. I learned a while ago that webcams will pick up IR light but those aren’t too convenient to take into the field. I suppose if you had a little netbook with a built in webcam that might do the trick but I’ve never tried it. I discovered that my BlackBerry makes for a decent enough IR camera for what we had planned. The facetime camera on an iPhone might work if you are patient. Many cameras have a built in IR filter. You can test your camera by viewing the front of a remote control through your camera as you push the buttons. If you see a light then your
camera will work to view IR light. You can also use cameras that have a “night vision” mode. As you can tell it’s not easy finding a way to view infra-red light. If you choose to build and IR cache it will be important to provide sufficient details in the description relative to your difficulty rating to allow people to find the cache. If you set your difficulty rating at 5 then you might not need to provide too many clues on how to solve the cache.
The trick to making an IR cache is finding plastic that is opaque to white light but easily transmits IR light. Black or smoked plastics work best. I used multiple layers of a red plastic. It is very hard to pass white light through multiple layers but the IR easily passes. Remember that light can pass in both directions. Determined geocachers will try and shine a light through your materials. You should always block at least one side so that light cannot be place under the clue and shine up through the blocking material.
Some cameras, mostly older video cameras, come with a built in IR illuminator. If your camera has a “Night Shot” or “Night Mode” you might have the features you need. Infra-red caches work at night because of darkness. There tends to be too much infra-red light during the day thus washing out weak IR sources used in a geocache. If you’ve ever tried to use your “night shot” setting during the day you’ll know what I mean. Many modern cameras, including those in the iPhone have a built in IR filter that blocks IR light. These cameras are not the best for finding IR clues.
These are just a couple of ways that you can use infra-red in the creation of your night cache. Be creative!