BH-A21 UV-Cut Longpass Filter
60 % colour-neutral transmission from 400 – 700 nm, < 1 % UV below 320 nm—BH-A21 keeps every hue bright while dumping harmful ultraviolet.
- Passband: ≈ 60 % T (flat) 400 – 700 nm
- UV block: < 1 % T below 320 nm (cut-on ≈ 345 nm)
- Warm-IR lift: ~70 % T @ 800 nm adds gentle warmth
- Angle range: < 5 nm spectral shift up to 45 ° AOI
- Wavefront: λ/10 P-V @ 632 nm (1″ aperture)
- Durability: Dense IBS stack, ≥ 10 H pencil; humidity & solvent resistant
- Formats: 5 – 450 mm, 0.5 – 3 mm on Borofloat®, Eagle XG, D 263 T, fused silica
Learn more
BH-A21 is KUPO’s go-to UV-cut filter for venues that demand
true-to-life colour and UV safety. The dielectric stack rejects
hazardous near-UV—holding transmission below 1 % to roughly 320 nm—then
accelerates past 40 % by 350 nm and flattens into a smooth 60 ± 2 % plateau
right across the visible rainbow. Beyond 650 nm the curve lifts toward
70 % at 800 nm, adding a subtle warmth that film and stage designers
often appreciate.
The coating’s angular stability keeps spectra tight even when optics are
tilted to 45 °, making BH-A21 equally at home in compact light engines,
architectural fixtures and off-axis machine-vision rigs. Dense
ion-beam-sputtered oxides shrug off heat, humidity and aggressive
cleaning, while λ/10 substrates protect image sharpness in
high-resolution systems.
Typical uses: UV-safe stage & architectural lighting,
colour-critical photography or broadcast, fluorescence and bio-imaging
setups requiring low-UV backgrounds, machine-vision lines where UV noise
fogs sensors, and outdoor luminaires that must meet safety regs without
colour distortion.
Need a different cut-on edge, ultra-thin glass, or dual-side AR?
KUPO’s in-house IBS chambers can tweak BH-A21 and ship prototypes in as
little as one week.
Description
BH-A21 is KUPO Optics’ workhorse filter when you need every colour of the rainbow—yet none of the stray ultraviolet that fogs images, fades gels, or irritates eyes. Transmission climbs steeply at roughly 345 nm, rockets past 40 % by 350 nm, and levels into a smooth ~60 % plateau all the way across the visible band. Beyond 650 nm the curve lifts again, topping out near 70 % at 800 nm, adding a touch of warmth without distorting white balance. This neutral, ripple-free profile makes BH-A21 a natural fit anywhere “true-to-life” colour and UV safety have to coexist.
Key Advantages
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Full-Spectrum Neutrality – ≈60 % flat transmission from 400-700 nm preserves accurate colour rendition for cameras, spectrometers, and the human eye.
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Aggressive UV Rejection – <1 % below ~320 nm safeguards sensors, biological samples, and operators from harmful near-UV.
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Angle-Friendly Coating – Spectral shift stays minor all the way to 45 °, perfect for compact optical paths, tilted fixtures, or off-axis illumination.
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Optical-Grade Build – λ/10 flatness and low scatter on polished glass keep wave fronts tight in laser or high-resolution imaging tasks.
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Fast Stock, Easy Custom – Standard diameters and square cuts ship quickly from Taipei; special sizes, thicknesses, or AOI-tuned versions can be engineered within days.
Typical Applications
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Stage & Architectural Lighting – Pass the full visible output while stripping UV that degrades fabrics, gels, and finishes.
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Cinema, Broadcast & Photography – Maintain colour consistency across mixed light sources; prevent UV spill that can haze lenses or over-expose sensors.
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Fluorescence & Bio-Imaging – Capture excitation and emission bands with minimal UV background, improving signal-to-noise.
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Machine Vision & Robotics – Ensure colour-true inspection under LED or mixed illumination without UV-induced sensor noise.
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Outdoor & Industrial Fixtures – Dielectric stack shrugs off heat, humidity, and cleaning solvents, delivering long-term reliability.
Need a different cut-on wavelength, special substrate, or unique form-factor? Reach out to KUPO Optics—our engineering team can tweak BH-A21 to match your design, often delivering prototypes the same week.
