The fact is that most of UFOs are invisible. In the 1950s Trevor James Constable photograped invisible UFOs using infra-red film. By using infra-red film in his cameras he discovered UFOs that exist in a light spectrum that cannot be seen to the naked eye...
Here is the movie:
A short video excerpt from the documentary, "UFO: Greatest Story Ever Denied". This video introduces startling evidence that suggest most UFO are actually invisible to the naked eye, but are only visible in the Infrared Light Spectrum. Ga naar deze website (onderaan): http://www.disclose.tv/viewvideo/1099/Invisible_UFOs/">http://www.disclose.tv/viewvideo/1099/Invisible_UFOs/">http://www.disclose.tv/viewvideo/1099/Invisible_UFOs/