Technical Reference 5. Optics WETStar s optical path begins with the 2 blue LED light sources located near the top of the flow tube. The LEDs are directly across from each other, providing a uniform excitation light field. The LEDs emit wideband output light centered at approximately 460 nm. This light is channeled through blue interference filters, which reject any red light emitted by the LEDs.
Fluoresced light is detected by a silicon photodiode detector.
This voltage is proportional to the chlorophyll concentration of the sample measured. WETStar is primarily designed to measure the concentration of chlorophyll containing phytoplankton which absorb light of wavelengths between 400 and 520 nm and emit light between 670 and 730 nm. These filters are used to discriminate against scattered blue light, allowing only the red fluoresced light to pass through to the detector. A mirror and lens help optimize the detector performance. A sketch of the optical light path is provided in Figure 2.