Early 19th-century photography was only able to record light falling in the blue and the ultraviolet portion of the electromagnetic spectrum. This very limited spectral range is best seen in the blank white skies in landscape photography in the mid-19th century.  By the 1880s and following the addition of sensitizing dyes to silver gelatin dry plates, improvements to photographic emulsions permitted photographers to record subjects from the ultraviolet into the green portions of the visible light spectrum. By the early 20th century, panchromatic emulsions appeared on the market. These new emulsions were sensitive to the entire visible light spectrum, improvements that ushered in the first viable color photographs, and the epic landscapes of Ansel Adams, as seen towering cloudscapes over Yosemite National Park.  Both achievements are the direct result of the introduction of panchromatic emulsions.
The advent of advanced digital imaging tools has expanded photographers’ ability to visually explore greater portions of the electromagnetic spectrum. The electromagnetic spectrum is the range of all types of electromagnetic radiation that travels and spreads. Visible light is just a small part of the electromagnetic spectrum and refers to the light that we can see. Other types of radiation include radio waves microwaves, infrared light, visible light ultraviolet light and X-rays.
Photographers and artists are experimenting with photographing subjects that are literally beyond human sight, recording scenes in “false colors” that are not grounded in human perception.  In most cases, photographers are using traditional digital cameras which are modified to remove UV and Infrared filters from the sensors, or using external infrared filters mounted on their lenses. The unusual and unpredictable colors achieved through these experiments are fascinating.
In the two slide shows presented above and below, a Panasonic Lumix G-9 mirrorless camera modified for full-spectrum capture was fitted with an external mounted LifePixel Enhanced Color Infrared 665 nm filter over a Pansonic Lumix F2.8 lens. Each photograph was color corrected and intuitively adjusted using Adobe Photoshop.
Digital camera sensors are inherently sensitive to infrared light, visible light ultra-violet light. Infrared radiation can make conventional digital photographs pink or fuzzy because infrared focuses on a slightly different point than visible light wavelengths. To improve visible-light imaging, digital camera manufacturers insert an infrared-blocking filter or IR-cutoff filter in front of the digital camera sensor to block most infrared light and improve image quality. The IR-cutoff filter does not block all infrared wavelengths, and most digital cameras can still record infrared radiation with the use of a filter—typically a deep red Hoya R72 or a true IR-passing filter such as an 87-series opaque filter. Because so much light is blocked with this method, long exposure times (sometimes approaching 30 seconds) are required.
With the removal of the infrared-blocking filter, digital camera sensors will record into the infrared spectrum and allow handheld photography with normal metering and focusing functions. Some early digital cameras such as the Olympus 2020z and C-3000 series, the Nikon 800 and 950 Coolpix, the Canon S10, the Kodak 260, and the Minolta Dimage 7 have become prized for their high infrared sensitivity. After 2004, IR-blocking filters became much more effective and typically cameras now require the removal of the IR-blocking filter in order to use them for infrared photography.  Several companies specialize in infrared conversion and provide prices and information for specific models. 
You can test the infrared sensitivity of your camera by pointing a remote control toward the lens and see if the beam registers in the camera’s LCD monitor. Next, you may want to test your camera by shooting with a Hoya R72 filter. You will know very quickly if your camera will record enough of the infrared spectrum to be serviceable for IR photography. IR radiation is highly unpredictable, varying with altitude and weather conditions.
In addition to modifying digital cameras to capture the portions of the infrared spectrum, cameras can be modified to replace the IR cut filter with a clear filter making the sensor sensitive to ultra-violet, visible, and infrared light, or what is referred to as full spectrum photography. Because of the increased sensitivity, full-spectrum modified cameras are useful with astrophotography and low light applications. In addition, once the camera is converted to full-spectrum recording, external filters can be placed over the lens to narrow the sensitivity to experiment with recording in specific segments of light.
Infrared Full-Spectrum Examples
In the examples shown below, external IR filters were placed over the lens of a Panasonic Lumix G-9 mirrorless camera converted to a full-spectrum recording. These examples were created at Washoe Lake near Carson City, Nevada in the early afternoon on a haze day. Each set of exposures include a raw, jpeg, and white balanced example. Several examples demonstrate post-processing with Silkpix Developer Studio 8 SE, a Panasonic camera raw processor, and further image adjustments using Adobe Photoshop. In addition, several examples include “channel swap” processing, a post-processing technique that switches the red and blue channels to achieve a distribution of blue light in the sky.
Full Spectrum Exposure (no external filter): Panasonic Lumix G-9 with Lumix F/2.8 12-60mm lens. The Lumix G-9 was modified to pass ultraviolet, visible, and infrared light (300nm – 1000nm).
Visible Light Exposure: LifePixel External Mounted Visible Bandpass Filter, Panasonic Lumix G-9 with Lumix F/2.8 12-60mm lens. This filter mounted on the lens blocks infrared and ultraviolet light.
Infrared Exposure: LifePixel Standard Infrared External Mounted 720nm filter, Panasonic Lumix G-9 with Lumix F/2.8 12-60mm lens.
Infrared Exposure: LifePixel Enhanced Color Infrared, equivalent to 665 nm filter Panasonic Lumix G-9 with Lumix F/2.8 12-60mm lens. This filter transmits more visible light than the LifePixel Standard Infrared filter.
Infrared Exposure: LifePixel Hyper Color 470nm filter, Panasonic Lumix G-9 with Lumix F/2.8 12-60mm lens. This filter combines visible and infrared light.
Infrared Exposure: LifePixel Super Blue External Mounted Filter, Panasonic Lumix G-9 with Lumix F/2.8 12-60mm lens. This filter passes Infrared (500—705nm) in addition to UV, and blue visible light.
Infrared Exposure: LifePixel Super Color External Mounted 590nm filter, Panasonic Lumix G-9 with Lumix F/2.8 12-60mm lens. This filter passes visible red light along with Infrared light. 
Infrared Exposure: Kolari Vision 550nm filter, Panasonic Lumix G-9 with Lumix F/2.8 12-60mm lens. This filter passes infrared (550nm) and visible light. 
Infrared Exposure: Runshuangyu Circular Infrared X-Ray Adjustable IR Pass Filter, 530nm (approximate), Panasonic Lumix G-9 with Lumix F/2.8 12-60mm lens. Similar in concept to a polarizing filter, this externally mounted filter marries a neutral density filter with a red long pass infrared filter and passes the infrared of wavelengths from 530nm, 590nm, 600nm, 630nm, 680nm, 720nm.
Infrared Exposure: Runshuangyu Circular Infrared X-Ray Adjustable IR Pass Filter, 600nm (approximate), Panasonic Lumix G-9 with Lumix F/2.8 12-60mm lens.
Infrared Exposure: Runshuangyu Circular Infrared X-Ray Adjustable IR Pass Filter, 720nm (approximate), Panasonic Lumix G-9 with Lumix F/2.8 12-60mm lens.
Working with either infrared film or digital camera infrared invites experimentation!
-  Carleton Watkins, Yosemite Valley From Inspiration Point, 1865-66 ; Mike Ware, “Light Sensitive Chemicals,” The Encyclopedia of 19th Century Photography, p. 857.
-  Ansel Adams, Yosemite Valley, 1934, [at Inspiration Point] https://www.sfmoma.org/artwork/57.941/
-  Infrared False Color photography (IRCP), Cultural Heritage Science Open Source, https://chsopensource.org/infrared-false-color-photography-irfc/
-  “IR and Digital Cameras, DP Answers.com. http://dpanswers.com/content/irphoto_sensors.php
-  IR and Full Spectrum Camera Conversions: Life Pixel, Spencers Camera, Kolari Vision.
-  Filter Choices, LifePixel, https://www.lifepixel.com/infrared-filters-choices
-  Kolari Vision, “Choosing an Infrared Filter, https://kolarivision.com/articles/choosing-a-filter/
- See Digital Infrared Photography. LifePixel.com, https://www.lifepixel.com/infrared-photography-primer