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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