It has long been speculated that if ghosts do manifest, they do so slightly within the infrared spectrum.  This is a possibility considering that infrared is a longer wavelength of the electromagnetic spectrum and requires less energy than light that is visible to our eyes.
We can see from about 400 nanometers to about 700+ nanometers.  Infrared extends past this.  Near infrared is what we are working with.  It ranges from just over 700 nanometers to past 1500 nanometers. 
We get orbs of light that are not visible to our eyes when the photo is taken.  Many of these can be explained away as dust or moisture, but a few may not be dust or moisture.  If we can’t see them, then why do they show up on our photos?  This is possibly due to the fact that film and digital cameras can “see” longer into the infrared spectrum than the human eye can.  This is easy to prove with a digital camera.  Point any remote control from a TV or VCR toward the lens of the camera.  Push any button on the remote and if you see a light in the view screen, your camera is sensitive to the near infrared spectrum.
If the supposition were true that some of these orbs are visible in the infrared spectrum, then it would stand to reason that infrared photography would be useful in capturing images of apparitions.   While there is no hard and fast data to prove this, it would stand to reason that this is an area for exploration. 
Infrared photography, however, is fraught with problems.  Infrared film is expensive.  I have found it on Amazon.com for $11.49-$11.99 per 36 exposure roll.  There is no guarantee that it will be in good condition when it arrives.  It is difficult to handle, as it must be kept cool at all times.  It must be loaded and unloaded in complete darkness.  Much experimentation is necessary to find what works best in your camera.  Unless you have your own darkroom, finding a lab that will develop it is very difficult.
  All of these problems make the practical use of infrared film very difficult for the average person.  Infrared photography did hold promise, however.  There are two photographs that proved that there was merit to the concept.
Paranormal investigator Dale Kaczmarek and his team captured a photograph of a woman sitting on a bench in Bachelor’s Grove cemetery in August of 1991.  The team that caught the photograph was using black and white infrared film.  This image is unusually clear and defined.  This photograph has been the subject of much debate, but to date no one has offered a “rational” explanation for this photograph.
In 1978, an unlikely haunting was happening in Sunnyvale, California.  A Toys-R-Us store was experiencing a great deal of paranormal phenomena.  Finally they contacted psychic Sylvia Brown who attempted to contact the entity there that she called “Yohan.”  She brought with her, on the night of the séance, a videographer and a still photographer using infrared film.  The resulting photograph shows what appears to be a person standing in the aisle looking toward the group that was present.  There are many differing opinions on the photograph, some supportive, some critical.  If this photograph is genuine, then it is one of the best shots ever taken of a supposed apparition.
All of this was running through my mind as I considered the dilemma of how to use infrared photography in our work as paranormal investigators.  I was further frustrated by the fact that one of my favorite sites, the Gettysburg National Military Park, was being restricted for nighttime photography.  Night access is very restricted on the field and most investigators take their photos at night.  At Gettysburg, this leaves only about an hour of darkness during the summer and slightly more during the off-season.
Most investigators use infrared cameras such as a Sony NightShot to film at night.   They can shoot infrared video and poor quality infrared stills with this camera, but what about day video and higher quality infrared shots?  We see moving orbs at night on the video cameras that we use because the NightShot is specifically designed to record in infrared when switched to the NightShot mode.  Again, there are many explanations for these orbs and you are entitled to your own opinion.  But, how do we film this phenomenon during the day?  Those images were still only possible with the use of standard infrared film, or were they?
My thought was that if a digital camera is infrared sensitive, I could possibly block out the visible light and leave only infrared.  I looked over literally hundreds of websites on photography and discovered that it is possible to take infrared photos in daylight without having to buy and process expensive infrared film.  The solution was simple, use an infrared filter on a digital camera.  How did I arrive at this conclusion?
Digital cameras use CCDs, or charged couple devices to record the image instead of film.  They are sensitive to the infrared spectrum.  If you place an infrared filter such as a Wratten 87B or Hoya R72 on the camera, you can filter out most visible light.  By doing this, you are now able to take infrared photos in broad daylight. 
There are some drawbacks to this system, however.  With digital still infrared photography, you need bright sunlight and a tripod.  The filter (I use a Hoya R72) requires a time exposure of ½ to 1 second.  This is too long for taking a freehand photo.  If your camera does not support the threads on the filter, simply use plumber’s Teflon tape to secure the filter in front of the lens.  It will not leave any adhesive residue when it is removed.
In addition to placing the camera on a tripod, it is necessary to take multiple photos from the same angle in order to compare them with others in the series.  It is also imperative to have at least one other person with you while you are taking photographs, that way; there is verification that no one was in the frame when the photo was taken.  Because of the distances involved, anyone in your frame, even at a distance will be visible.  Anyone moving in the distance will appear as a blur.  This is where multiple observers are a great asset to the session.
If you set a video camera next to your still camera, you can have a record of everything that transpired during your photography session.  This will also serve as verification of the events in front of the camera.
The first person outside of the Ghost Research Foundation to evaluate this new technique was Mark Nesbitt.  Mark is an author, historian, paranormal investigator and the foremost authority on the history and hauntings in Gettysburg.  I had taken a photo at Devil’s Den in Gettysburg that showed two apparitions that were not visible in the frame at the time the photo was taken.  Mark was kind enough to give us his opinion and permission to use it.

“No longer are ghost investigators limited to time restraints placed by historical sites; paranormal photographs can be taken in broad daylight and results can be seen practically instantaneously. The technique more than doubles the amount of time an investigator can work a site, increasing the odds of capturing the elusive full apparition, and proving, as we all know, that ghosts don’t just come out at night.”

Mark Nesbit

I have not been the only person to use this technique successfully.  Craig Rupp took a photograph on Little Round Top that shows an apparition looking over the rock that is home to General Warren’s statue.  A comparison photograph taken later, shows that the ground is currently too high to reproduce a similar effect.
Still cameras are not the only way to work with infrared in the daylight.  There are filters available for video cameras as well.  Most video cameras will accept a threaded filter.  I personally use a Sony TRV-480 with an M&K 1000 filter.  This allows me to use the NightShot feature in broad daylight without damage to the camera. 
Using infrared filters now gives paranormal investigators the ability to conduct investigations during the day at sites that are normally inaccessible at night.  Once more investigators start using these methods, I believe we will see some surprising results.
I would like to thank Mark Nesbitt for his support and professional opinion as well as his vast knowledge of the history and hauntings of Gettysburg.  I do believe that as researchers, if we share our knowledge, the field will definitely benefit from it.  Of course, as with any new methodology, more use and testing will be required to see what the full capabilities are.