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What is a Longpass Coated Optical Filter? A Complete Guide for Buyers

May 15,2026 | JINGYU OPTOELEC

What is a Longpass Coated Optical Filter

A Longpass Filter acts like a gatekeeper for light. It allows light waves longer than a specific wavelength (e.g., 640nm) to pass through freely, while blocking or reflecting shorter wavelengths (e.g., blue or UV light).

Think of it as a “optical sieve.” If you want only red or infrared light for hair removal or a red stage effect, a longpass filter gives you that pure, targeted light.

How Does It Work? The Magic of Optical Coating

The secret lies not in the glass itself, but in the **thin-film coating** applied to its surface.

The Process: Using vacuum deposition technology, dozens of nano-scale layers are coated onto high-quality glass (e.g., Schott glass or K9 optical glass).
The Principle (Interference): These layers are precisely designed to create light interference – canceling out unwanted short wavelengths while boosting the transmission of the desired long wavelengths.
The Result: A filter with>95% peak transmittance and sharp cut-off characteristics, ensuring high brightness and purity of light.

✅ No advanced coating process = no reliable longpass filter.

Key Specifications You Must Know (For Custom Orders)

When choosing or customizing a longpass filter, focus on these 4 parameters:

Specification What It Means in Plain English
Cut-On / Cut-Off Wavelength The “dividing line.” e.g., 640nm longpass = allows light longer than 640nm (orange/red) to pass.
Transmittance How much useful light gets through. >90%-95% is excellent for bright, efficient devices.
Blocking / Cut-Off Depth How well it blocks the short, unwanted light. OD2 (1% transmission) to OD4 (0.01%) are common.
Surface Quality (Scratch/Dig) The smoothness of the glass surface (e.g., 40/20 or 60/40). Affects clarity and lifespan.

Top 5 Filter Applications

They are not just lab equipment; they are key components in everyday devices.

1. Beauty & Aesthetic Devices (IPL/Hair Removal)
Goal: Remove hair, acne, or vascular lesions.
How it works: LP640nm / LP690nm longpass filters allow deep-penetrating infrared light to target hair follicles while blocking harmful UV/short blue light.

2. Stage & Entertainment Lighting
Goal: Create vivid, pure colors (red, orange, deep amber).
How it works: Moving heads, pattern projectors, and laser lights use longpass filters to cut off blue/green light, leaving only saturated reds and warm tones.

3. Laser Systems (e.g., 10.6µm CO2 lasers, 1064nm)
Goal: Combine or clean up laser beams.
How it works: Longpass filters can reflect a 532nm green aiming beam while passing a 1064nm infrared cutting beam – critical for safety and precision.

4. Machine Vision & Industrial Inspection
Goal: Enhance contrast for defect detection.
How it works: A longpass filter blocks ambient light but allows the specific color of a laser or LED signal to reach the camera sensor.

5. Security & Surveillance (Night Vision)
Goal: See clearly in darkness.
How it works: During the day, the filter blocks IR light for true colors. At night, it passes IR light from illuminators for clear black-and-white images.

Available Materials & Customization

Depending on your application (power, heat, wavelength range), you can choose the base glass:

Glass Material Best For Key Benefit
K9 (Optical Glass) Stage lights, general instruments Cost-effective, good optical performance
Schott Glass High-end medical/beauty devices Superior clarity and thermal stability
Fused Silica High-power lasers, UV to IR applications Extremely wide transmission range, very low thermal expansion
Sapphire Extreme environments (military, high-power) Very hard, scratch-resistant, high thermal conductivity

Custom Options:

  • Thickness: 0.21mm to 2.0mm (ultra-thin available)
  • Size: Any diameter or square shape (e.g., D20mm, 25x25mm)
  • Coating: AR coating on non-filter side to reduce reflection (up to 98% transmission)
  • Color & Logo: Custom silk-screen printing or UV ink logos

Why Choose a Professional Manufacturer

To ensure stable quality and reliable performance, choose a supplier with:

  • In-house coating machines (not just cutting/assembling)
  • Complete process chain: Cutting → Grinding → Polishing → Cleaning → Coating → Assembly → Inspection → Packaging
  • Testing equipment: Spectrophotometer to provide transmission curve reports with each batch
  • Cleanroom environment: Class 1000 or better for coating and assembly
  • Low MOQ and custom service: Flexible for prototypes or mass orders

A supplier without in-house coating cannot control the most critical part of a longpass filter.

Quick Summary

Question Answer
What does a longpass filter do? Allows long wavelengths (e.g., red/IR) through; blocks short ones (blue/UV).
Where is it used? IPL hair removal, stage lights, lasers, machine vision, night vision.
What specs matter most? Cut-on wavelength, transmittance (>90%), blocking depth.
Can I customize size/wavelength? Yes, most suppliers offer full customization with low MOQ.

Contact Us for Your Custom Longpass Filter

Whether you need a 640nm longpass filter for an IPL beauty device, a high-power laser beam combiner, or a stage lighting color filter, we can manufacture to your exact specifications.

✅ OEM/ODM Welcome  
✅ ISO Certified Facility  
✅ Free Technical Support  
✅ Fast Sample Delivery

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