Choosing the Right Optical Filters for Flawless Security Camera Images

Better Vision, Day or Night: A Guide to Security Camera Optical Filters

Modern security cameras are powerful, but their digital sensors see the world differently than our eyes do. They can detect light beyond the visible spectrum, like near-infrared (NIR) and ultraviolet (UV). While this is great for night vision, it can ruin daytime color, add hazy noise, and cause unwanted flare.

The solution is precise spectral management. As we say at KUPO Optics: Enhance surveillance systems with IR-cut filters for daytime color accuracy; Long-pass filters for superior night vision; and UV-cut filters to protect sensors and reduce noise.

This guide breaks down how each filter works, what to look for, and how to choose the perfect one for your system.

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What Do Optical Filters Actually Do?

Optical filters act as gatekeepers for light, shaping what reaches the camera sensor. By controlling the spectrum, you create a camera that delivers sharp, consistent, and reliable images no matter the lighting conditions.

• IR-Cut Filters: These are for daytime use. They pass the visible light we see while blocking the invisible near-infrared light that would otherwise make colors look washed out and unnatural.
• Long-Pass (IR-Pass) Filters: These are for nighttime use. They do the opposite: they block visible light and only let near-infrared light pass through, perfect for cameras using IR LEDs for illumination.
• UV-Cut Filters: These block harmful ultraviolet light, which can cause a blue haze in images and degrade a camera's internal components over time.
• Switchable Systems: Many "day/night" cameras use a mechanical system to place an IR-cut filter in front of the sensor during the day and remove it (or swap it for a long-pass filter) at night.

The bottom line: By managing the light spectrum, you get stable white balance, higher contrast, and better image quality in every scene.

IR-Cut Filters: For True-to-Life Daytime Color

Goal: To capture accurate, vibrant colors during the day by stopping invisible IR light from corrupting the image.

Without an IR-cut filter, your camera's sensor gets confused. Reds can look pink, greens appear muddy, and human skin tones are completely unnatural. An IR-cut filter solves this by preserving the visible spectrum while cutting out the problematic IR.

Key Benefits:

• Accurate Color: Prevents the reddish or pinkish color cast that plagues cameras without proper IR filtering.
• Natural Scenery: Keeps foliage, skies, and skin tones looking the way they should.
• Reduced Glare: When combined with our anti-reflection (AR) coatings, they minimize ghosting and reflections for a crisper image.

What to consider: When specifying an IR-cut filter, you’ll want to define the cut-off wavelength (typically around 650 nm) where it starts blocking IR light. We also account for your lens's f-number and viewing angle, as these can slightly shift how the filter performs.

Long-Pass (IR-Pass) Filters: For Crystal-Clear Night Vision

Goal: To maximize night vision performance by blocking distracting visible light and focusing the sensor only on IR illumination.

This filter is the key to powerful night vision. It works hand-in-hand with the camera’s IR LEDs (often 850 nm or 940 nm). By filtering out all visible light from streetlights or other sources, the camera can produce a high-contrast, low-noise monochrome image using only its own invisible light source.

Key Benefits:

• Boosted Night Sensitivity: Greatly improves the signal-to-noise ratio (SNR) for a cleaner, brighter image in the dark.
• Higher Contrast: Eliminates "light pollution" from visible sources, making it easier to identify subjects.
• Enhanced Covert Surveillance: Using a filter matched to a 940 nm LED makes the camera's illumination source nearly invisible to the human eye.

What to consider: The most important spec is the cut-on wavelength, which should be matched to your IR illuminator (e.g., an 850 nm cut-on for an 850 nm LED).

UV-Cut Filters: To Protect Your Sensor and Sharpen Your Image

Goal: To block invisible UV light that can reduce image quality and damage camera components.

UV light is everywhere, and while we can't see it, your camera's sensor can. This unwanted light can create a hazy blue fog, especially with wide-angle lenses, and can slowly damage the adhesives and coatings inside the lens assembly over time.

Key Benefits:

• Reduced Haze: Improves image clarity and contrast by cutting out atmospheric blue haze.
• Component Protection: Helps protect sensitive internal adhesives and coatings from UV-induced yellowing and degradation.
• Versatility: Can be combined with an IR-cut filter to create a single "UV-IR cut" filter that only allows visible light to pass.

What to consider: For applications requiring high durability, fused silica is an excellent substrate choice due to its superior thermal stability and resistance to UV degradation.

How to Specify the Perfect Filter (Without the Guesswork)

Defining a filter doesn't have to be complex. Here are some typical starting points we use to build a custom solution for our clients.

• For a typical IR-Cut Filter (Day Mode): You would look for a filter that passes light from roughly 420 nm to 650 nm with high transmission (90-95%). It should then strongly block IR light from 700 nm to 1100 nm. A common material is B270/BK7 glass with anti-reflection coatings on both sides.
• For a typical 850 nm Long-Pass Filter (Night Mode): You would specify a cut-on wavelength around 850 nm±10 nm. It should strongly block visible light to prevent interference and transmit light well into the IR spectrum to match the sensor's sensitivity.
• For a typical UV-Cut Filter: You'd want it to block everything below about 390 nm±10 nm while allowing all visible light from 400 nm to 700 nm to pass through with minimal reflection.

Note: These values are examples. We tune the final specifications to your exact sensor, lens, LED, and housing.

Coatings and Durability Make All the Difference

A filter is only as good as its coatings and construction.

• Anti-Reflection (AR) Coatings: These are critical. Our dual-side AR coatings can boost light transmission to over 95% and slash distracting ghost images and flare.
• Environmental Robustness: For outdoor cameras, we offer designs that are tested against humidity, salt-fog, abrasion, and temperature changes.
• Hydrophobic/Oleophobic Coatings: These optional coatings keep water, oil, and fingerprints off the lens, reducing maintenance needs.

We Make Integration Easy

KUPO Optics can deliver filters in whatever form factor you need to simplify your assembly process.

• Custom Shapes and Sizes: Round, square, rectangular, or completely custom silhouettes.
• Mounting Solutions: We offer filters with adhesive frames, in retaining rings, or as part of an integrated sensor window assembly.
• Matched Sets: For day/night cameras, we can provide kitted filter sets to ensure perfect performance.

Summary

Getting your camera's spectral mix right is one of the most cost-effective ways to guarantee high performance.

• IR-cut filters deliver daytime color accuracy.
• Long-pass filters raise night sensitivity.
• UV-cut filters improve contrast and protect your hardware.

With the right specifications for wavelength, materials, and coatings, your surveillance system can achieve consistent, field-ready performance.

If you’re ready to see the difference the right filter can make, send us your requirements. We’ll help you design a production-ready solution with the data to back it up.

[Request a sample or custom size today!]

FAQs

1) What’s the practical difference between IR-cut, long-pass, and UV-cut? An IR-cut passes visible light and blocks NIR for accurate daytime color. A long-pass blocks visible and passes NIR for night vision with IR LEDs. A UV-cut blocks ultraviolet to reduce blue haze and help protect materials. Many cameras use an IR-cut by day and a long-pass or no filter at night.

2) How do I pick a cut-on/cut-off wavelength? Match the filter to your illumination source and sensor's sensitivity. For daytime color, a cut-off around 650 nm is common. For use with 850 nm IR LEDs, an 850 nm cut-on is typical. We can help you verify the ideal choice with a transmission curve analysis.

3) Will an IR-cut filter reduce low-light performance? By definition, yes—it attenuates the near-infrared light that sensors use in low light. That’s why day/night cameras are designed to remove the IR-cut filter at night. During the day, however, it is essential for good color.

4) How much does the light's angle (AOI) matter? It matters quite a bit. Filters can behave differently depending on the angle at which light strikes them. This effect is more pronounced in lenses with a wide aperture (low f-number). We test and design filters based on your specific optical setup to ensure performance is consistent across the entire image.

5) Which glass material is best? B270 and BK7 are excellent, cost-effective choices for general-purpose visible and NIR applications. Fused silica is preferred when superior UV durability and thermal stability are critical.

6) Do anti-reflection (AR) coatings really matter? Absolutely. A good dual-side AR coating can reduce reflections from over 4% per surface to less than 1%. This significantly improves contrast, boosts light transmission, and eliminates ghost images, especially in compact camera modules.

7) Can KUPO machine custom shapes or pre-mount filters? Yes. We provide custom glass machining, edge treatments, adhesive frames, and complete sensor window assemblies to reduce your assembly time and improve reliability.