Longpass Filters
A filter that transmits wavelengths above a defined cut-on point and blocks shorter wavelengths.
Share requirements, quantities and a drawing if available. Specifications and supply terms require confirmation.
Overview
A longpass filter transmits light above a defined 'cut-on' wavelength while blocking shorter wavelengths, the opposite behavior of a shortpass filter. This one-edge design (versus a bandpass filter's two edges) makes it a common choice where the goal is simply to block visible or UV light while letting infrared through, or vice versa, rather than isolating one narrow band. Procurement review should center on transmitting wavelengths above a cutoff while rejecting the shorter band.
Key Selection Points
- Single cut-on edge design, simpler than a two-edge bandpass filter for applications that only need one cutoff
- Common in IR imaging, fluorescence emission filtering and UV/visible blocking applications
Applications
Longpass filters are used in IR imaging systems to block visible light, in fluorescence microscopy to pass emitted light while blocking the excitation wavelength, and generally wherever an application needs everything above one wavelength and nothing below it.
Spectral Performance
This module explains which spectral variables must be defined before measured performance can be reviewed. For Longpass Filters, the module focuses on transmitting wavelengths above a cutoff while rejecting the shorter band.
- Review measured performance against supplier or test-lab data tied to the exact configuration.
- Record wavelength region, angle of incidence and polarization with the measurement context.
- Confirm transmission, reflectance and blocking requirements against approved evidence for the selected configuration.
- Product-specific review: connect cut-on wavelength with long-wavelength pass region and document the trade-off against a bandpass filter.
Prepare a product-specific enquiry
Include the requirements you know and identify any points that need confirmation.
| RFQ input | What to provide |
|---|---|
| Input 1 | Define the buyer objective for Longpass Filters: transmitting wavelengths above a cutoff while rejecting the shorter band. |
| Input 2 | Optical inputs: cut-on wavelength; transition slope. |
| Input 3 | Geometry and interface: long-wavelength pass region; short-wavelength blocking region and AOI. |
| Input 4 | Special review note: state cut-on definition, usable pass region, blocking interval and AOI. |
| Input 5 | State quantity and project stage without assuming MOQ, inventory or delivery timing. |
| Input 6 | Name the drawing revision and acceptance evidence required for review. |
Frequently Asked Questions
What is the difference between a longpass and a shortpass filter?
A longpass filter transmits everything above its cut-on wavelength and blocks shorter wavelengths; a shortpass filter does the reverse, transmitting everything below its cutoff and blocking longer wavelengths.
Is a longpass filter the same as an IR filter?
An 'IR longpass filter' is simply a longpass filter with its cut-on wavelength set in the infrared range — it is the same product category, described by its application band rather than a separate product.
Which specification should be fixed first for Longpass Filters?
Begin with cut-on wavelength. It determines how transition slope and long-wavelength pass region should be evaluated before the mechanical details are finalized.
When is Longpass Filters a better fit than a bandpass filter?
Choose between them by testing the requirement for transmitting wavelengths above a cutoff while rejecting the shorter band. If that requirement is absent, the comparison product may provide a simpler procurement path.
What should an RFQ for Longpass Filters include?
State cut-on definition, usable pass region, blocking interval and AOI. Also include quantity, drawing revision and the required acceptance evidence. Final availability is confirmed during quotation.
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