What light does a filter transmit, and what light does it absorb?

• Red filter: Mainly transmits red wavelength band (approximately 620–750 nm), and absorbs or blocks green and blue light.
• Blue filter: Transmits blue wavelength band (approximately 450–495 nm), and absorbs or blocks red and green light.
• Green filter: Transmits green wavelength band (approximately 495–570 nm), and absorbs light of other colors.
• Band-pass filter: Transmits only a narrow range of wavelengths, for example, 530–550 nm.
• Long-pass filter: Only allows light with wavelengths longer than a specific value to pass through (e.g., >600 nm).
• Short-pass filter: Only allows light with wavelengths shorter than a specific value to pass through (e.g., <400 nm).

• Absorbed and converted into thermal energy (e.g., colored glass filters);
• Or reflected (especially interference filters with multi-layer film structures).

Example

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

If you are selecting filters for image processing or machine vision analysis, please clarify your application goals (such as detecting red defects or ultraviolet response), and I can recommend the appropriate filter for you.

Polarizer

The function of a polarizer is to control and screen the polarization direction of light. It only allows polarized light in a specific direction to pass through, while light in other directions is absorbed or reflected.

Simple explanation

Unfiltered natural light (such as sunlight and lamplight) is unpolarized light, whose electromagnetic waves vibrate in all directions.A polarizer performs directional filtering on the vibration direction of light waves.

Main functions of polarizers

✅ 1. Eliminate reflected light and glareWidely used in cameras, polarized glasses, vehicle windows, screen protective films and other products.The reflected light generated on the surface of water, glass, metal and other objects is mostly polarized light. A polarizer can effectively filter out such reflected light and improve image clarity.

In photography, a CPL polarizing lens removes reflections on water surfaces and glass, making underwater scenes and indoor views clearer.

Application cases:Shooting lake surfaces in sunny conditions — a polarizer helps observe fish and stones at the bottom of the water;Shooting vehicles — eliminate glare and reflections on the windshield.

✅ 2. Enhance contrast and color saturationAfter removing scattered light and reflected light, colors appear deeper, brighter and purer.Commonly applied in outdoor photography, remote sensing imaging, medical imaging and other fields.

✅ 3. Light control in display and optical systemsLCD screens rely on polarizers to adjust the brightness of each pixel. Without polarizers, LCDs cannot display images normally.In precision optical instruments, polarizers are used for light intensity adjustment and material property analysis (stress, crystal orientation, etc.).

✅ 4. Stress detection and material inspectionUnder polarized light, internal mechanical stress of transparent materials (plastics, glass) will change the polarization state of light, presenting distinct color differences in images for intuitive analysis.This detection method is defined as polarized light interference stress inspection.

Working principle

Polarizers are generally made of stretched polymer materials (e.g. PVA). This special structural feature endows the material with directional absorption characteristics.It selectively transmits light waves vibrating in a fixed direction, and absorbs or blocks all light waves with other vibration angles.

Application Summary:

Polarized sunglasses: Eliminate glare from water and glass surfaces