IR-Cut, UV-Cut or UV/IR-Cut: Choosing a Filter for Your Camera

A camera does not necessarily see the same spectrum as your eyes. Its sensor, lens, internal filters and illumination work together to determine the recorded image. Adding a filter can change that response, but first you need to know which wavelengths are causing trouble.

Choose what to block by first deciding what you want to measure. Infrared may be unwanted in one camera and the useful signal in another.

Three names, three filtering tasks

IR-cut means reducing infrared transmission while retaining the intended shorter-wavelength band. It is commonly relevant when a visible-light camera responds to infrared that affects the image.

UV-cut means reducing ultraviolet transmission while retaining the intended longer-wavelength band. It does not automatically remove infrared.

UV/IR-cut combines lower- and upper-wavelength limits around a transmitted region, often the visible band. Check the actual curve: these names do not define identical edges or blocking levels across all products.

For visible color imaging, inspect the complete camera

If color accuracy is the objective, start with the camera manufacturer's information about the installed optical stack. Many cameras already include infrared control. Adding another filter without checking the first can reduce useful light or alter the response unnecessarily.

If you compare filtered and unfiltered images, keep illumination and camera settings consistent. A filter may improve an unwanted spectral contribution, but it cannot substitute for an appropriate color-calibration workflow.

For near-infrared imaging, do not block your own signal

A system illuminated at 850 nm needs that light to reach a compatible detector. A suitable bandpass or longpass may help select it. An infrared-cut filter in the optical path can work against that goal.

Check internal camera filters as well as external ones. A filter placed on the front of a lens cannot recover wavelengths that another component rejects. Any camera modification also needs an assessment of focus and the manufacturer's requirements.

“UV-cut” is not a general cure for poor image quality

Haze, flare, blur and low contrast have several possible causes. Before choosing UV filtering, establish that ultraviolet light reaches the detector and contributes to the problem. Lighting geometry, surface reflections, lens performance or contamination may be more relevant.

Similarly, a UV/IR-cut filter will not remove visible background that overlaps the useful visible signal. The spectral response needs to match the specific task.

Four checks for a shortlist

• Useful band: what wavelengths should the camera record?
• Unwanted band: what reaches the system that you want to reduce?
• Operating geometry: does the stated curve apply at your working angle and ray cone?
• Coverage: do the measurements extend across the detector's relevant response?

For filtering that redirects rather than absorbs infrared, also consider where the reflected light goes. High-power operation requires its own thermal and optical assessment.

Browse KUPO hot mirror and UV/IR-cut designs, or explore wavelength-selection filters for other pass and cut functions. Send your camera model, illumination and an example of the image problem if you are unsure which function you need.