Infrared goggles, or IR goggles, are devices that allow the wearer to view the infrared radiation, also called thermal or heat radiation, emitted by or reflected by objects. They allow individuals to see beyond the usual visual spectrum that the human eye can perceive. IR goggles are binocular, meaning they have two eyepieces. They are available in a number of styles, from simple elastic-banded goggles to the complex and expensive night-vision devices (NVDs) used by military and police forces around the world.
The electromagnetic radiation, or light, referred to as infrared has a longer wavelength than the visible light that humans can see. On the electromagnetic spectrum, it lies between visible light and microwave radiation. The infrared light that is closest in wavelength to visible light is called "near infrared" while the infrared wavelengths that lie closer to microwaves are called "far infrared."
Thermal radiation, or what humans experience as heat, is far infrared radiation. Near infrared cannot be seen or touched and is commonly used in remote controls. The most important feature of thermal infrared is that it is emitted by an object.
IR goggles take advantage of ambient infrared radiation. This allows the wearer to see objects that emit in the infrared or reflect it. Infrared goggles can detect infrared radiation even in a room that may seem completely dark to the unaided human eye.
The more expensive and complex NVDs use a power source to intensify ambient infrared and visible light as they pass through a series of lenses and filters. Their use of an image intensifier differentiates NVDs from other types of night vision and infrared devices. These particular night vision goggles contain two eyepieces, a power source, a photocathode tube, or image intensifier, and a lens. The image intensifiers, using chemical and electrical processes, amplify the infrared and visible light passing through the lenses by thousands of times.
Less expensive IR goggles only use filters and a lens. They are not electrically powered as there is no intensifier tube that requires a power source. As a result, inexpensive IR goggles are not capable of amplifying the infrared light to the same degree as a night-vision device. A pair of IR goggles can be crafted using welding goggles with removable lenses and sheets of filter gel. Different types of filters can be used, some of which allow a little bit of visible light to pass through, others, which block it completely.