In the 1980s I worked for marine biologists who used fluorometers to measure chlorophyll in the open ocean at concentrations of micrograms per litre in seawater. The lab instuments used a photomultiplier tube detector -which was impractical to package for conducting chlorophyll profiles of the water column using an instument package the was to measure down to 200 meters or so. So, the instrument we used made by Sea-Tech which used xenon flash excitation and a large photodiode along with optical filters to limit the excitation band to around 425nm and the receiver band to 685nm. The receiver had a sample and hold/peak detector to capture the received 685nm energy flourescing from any chlorophyll bearing biomass in the water.
It worked but it was noisy. It was difficult to eliminate noise emmitted by the flash circuit, and the sample and hold - not to mention the clumpy nature of chlorophyll bearing criters distributed in the water column.
These were hand built, expensive instruments. I made an attempt to build a cheapo instrument that used blue LEDs as emmitters and a red LED as a detector. The red LED was used as a photo generated current source meant to drive a current-to-frequency converter (Op Amp + 7555 timer chip). Frequency variation was to offer some measure of chlorophyll content. The setup would be calibrated against the lab fluorometer. I never got past a protoype. It sort of worked but was probably not sensitive enough.
In the 1980s I worked for marine biologists who used fluorometers to measure chlorophyll in the open ocean at concentrations of micrograms per litre in seawater. The lab instuments used a photomultiplier tube detector -which was impractical to package for conducting chlorophyll profiles of the water column using an instument package the was to measure down to 200 meters or so. So, the instrument we used made by Sea-Tech which used xenon flash excitation and a large photodiode along with optical filters to limit the excitation band to around 425nm and the receiver band to 685nm. The receiver had a sample and hold/peak detector to capture the received 685nm energy flourescing from any chlorophyll bearing biomass in the water.
It worked but it was noisy. It was difficult to eliminate noise emmitted by the flash circuit, and the sample and hold - not to mention the clumpy nature of chlorophyll bearing criters distributed in the water column.
These were hand built, expensive instruments. I made an attempt to build a cheapo instrument that used blue LEDs as emmitters and a red LED as a detector. The red LED was used as a photo generated current source meant to drive a current-to-frequency converter (Op Amp + 7555 timer chip). Frequency variation was to offer some measure of chlorophyll content. The setup would be calibrated against the lab fluorometer. I never got past a protoype. It sort of worked but was probably not sensitive enough.
I'm sure you know this, but peanut butter phosphoresces (relatively) strongly