LP675 롱패스 필터(T>85%@685-1750nm, OD5@200-665nm)

Chlorophyll Fluorescence Imaging (Plant Health)

This is one of the most common uses for a cut-on wavelength of 675nm.

• The Science: Chlorophyll $a$ absorbs blue and red light and re-emits (fluoresces) faint light at approximately 685nm (peak 1) and 730nm (peak 2).
• How the Filter Works: The filter blocks the powerful red excitation light (usually <660nm) used to drive the photosynthesis but passes the faint fluorescence emission (>680nm) to the detector.
• Why OD5 is needed: The fluorescence signal is very weak. You need Optical Density 5 (100,000x blocking) to ensure the bright excitation light does not overwhelm the sensor.

Compatible Light Sources

A. Excitation Sources (Light the filter MUST BLOCK)

• Deep Red LEDs (630nm - 650nm): This is the ideal match. A high-power 640nm LED is perfect for exciting Chlorophyll or Alexa Fluor 660. The filter will block the LED light, leaving only the fluorescence.
• Helium-Neon Laser (633nm): Standard gas laser. The filter blocks this line effectively (OD5).
• Red Diode Lasers (635nm - 640nm): Common in pointers and industrial modules.
• Warning on 660nm LEDs: A standard "660nm" LED often has a spectral width of ±20nm. This means the "tail" of the LED emission could bleed past 665nm and leak through the filter. If you use a 660nm source, you need a Shortpass Excitation Filter (e.g., SP660) in front of the light source to "clean up" the tail.

B. Transmissive Sources (Light the filter MUST PASS)

If you are using this for machine vision (surveillance, sorting) or backlighting:

• NIR LEDs (730nm, 850nm, 940nm): The filter will pass >90% of this light.
• 1064nm Nd:YAG Laser: The filter passes this wavelength (up to 1750nm limit), making it useful as a "laser line clean-up" filter that removes visible flashlamps or aiming beams while passing the infrared laser.

Application: Deep Red / NIR Fluorescence Microscopy

In life sciences, this filter serves as an Emission Filter for dyes that fluoresce in the far-red/Near-Infrared (NIR) window.

• Target Fluorophores:Cy5.5: Excitation ~675nm / Emission ~694nm. (Note: This filter is tight for Cy5.5 excitation; see light sources below).Alexa Fluor 660: Excitation ~663nm / Emission ~690nm.Alexa Fluor 680: Excitation ~679nm / Emission ~702nm.IRDye 680: Excitation ~680nm / Emission ~694nm.

Recommended Light Sources

• High-Power 640nm LED: This is the industry standard for this region. It is safely blocked by the LP675 filter (which blocks up to 665nm).
• 635nm - 640nm Laser: Lasers have a very narrow spectral line, ensuring no light "leaks" past the 665nm blocking edge.