Working Principle of Optical Filters-Knowledge Encyclopedia-Shenzhen Kai Mo Rui Electronic Technology Co. LTD

Working Principle of Optical Filters

Source：Shenzhen Kai Mo Rui Electronic Technology Co. LTD2026-06-29

An optical filter operates by selectively transmitting light of specific wavelengths while absorbing or reflecting light at other wavelengths. Its core working mechanism relies on the optical properties of materials: different substances and structural designs exhibit distinct transmittance and absorbance for light across various wavelengths.

Which Wavelengths Do Filters Transmit, and Which Do They Block?

✅ 1. Transmission: Permit light of designated wavelengths to pass through

Filters are engineered to only allow a targeted segment of the light spectrum (such as red, green, blue, infrared, etc.) to pass:

Red Filter: Primarily transmits red light band (approx. 620–750 nm), absorbs or blocks green and blue light.
Blue Filter: Transmits blue light band (approx. 450–495 nm), absorbs or blocks red and green light.
Green Filter: Transmits green light band (approx. 495–570 nm), absorbs light of other colors.
Bandpass Filter: Only transmits a narrow wavelength range, e.g., 530–550 nm.
Long-pass Filter: Allows only wavelengths longer than a threshold value to pass (e.g., >600 nm).
Short-pass Filter: Allows only wavelengths shorter than a threshold value to pass (e.g., <400 nm).

❌ 2. Absorption / Blocking: Restrict unwanted wavelengths

Light wavelengths not transmitted will be disposed of in two ways:

Absorbed and converted into thermal energy (typical for colored glass filters);
Reflected (especially interference filters with multi-layer film structures).

Example: Green Filter

Transmitted light: 495–570 nm (green spectrum)
Absorbed/reflected light: Red light (>620 nm), blue light (<495 nm)

Cameras or human eyes can only perceive green tones through this filter, with all other colors filtered out.

If you need to select filters for image processing or machine vision applications, share your application goal (such as red defect inspection or ultraviolet response detection), and I can recommend the matching filter solution for you.

Polarizers

A polarizer functions to regulate and screen the polarization direction of light: it only permits polarized light vibrating along a specific axis to pass, while absorbing or reflecting light oscillating in all other directions.

Simple Explanation

Unfiltered natural light (sunlight, indoor lamp light, etc.) is unpolarized light, meaning its electromagnetic waves vibrate in all orientations.A polarizer acts as a directional sieve to filter the vibration plane of light waves.

Core Functions of Polarizers

Eliminate reflected light and glareWidely applied in cameras, polarized sunglasses, vehicle windows, screen protective films, etc.Reflections off water surfaces, glass, metal and other surfaces are mostly polarized light; polarizers can effectively suppress such reflections and improve overall image clarity.In photography, circular polarizing (CPL) filters remove reflections on water or glass, revealing clearer underwater or indoor details.

Application case 1: Shooting a lake in direct sunlight; a polarizer enables clear visibility of fish and stones beneath the water surface.
Application case 2: Shooting vehicles to eliminate distracting reflections on windshields.

Boost image contrast and color saturationAfter removing scattered and reflected stray light, colors appear deeper, richer and purer.Commonly used in outdoor photography, remote sensing imaging, medical imaging and other fields.
Light modulation for display and optical systemsLiquid Crystal Displays (LCDs) rely on polarizers to control the brightness of individual pixels; an LCD cannot form visible images without polarizer components.In scientific instruments, polarizers are used for light intensity adjustment and material property analysis (stress distribution, crystal orientation identification, etc.).
Stress analysis and material inspectionUnder polarized illumination, internal mechanical stress inside transparent materials (e.g., plastic) alters light polarization states, generating visible color variations in captured images for analysis. This technique is known as polarized light interference stress testing.

Brief Working Principle of Polarizers

Polarizers are fabricated from stretched polymer materials (e.g., polyvinyl alcohol, PVA), which possess directional light absorption/conductive properties along one axis.This structural design allows light vibrating along a designated orientation to transmit through, while absorbing or reflecting light waves with other vibration angles.