Optical cannabinoid UV measurement

So this is probably more for the nerdiest among us, but I found a paper that shows absorbance of different cannabinoids. I was looking it over and I think building an inexpensive detector would be feasible:


275-280nm LEDs are easy to find, but it seems like all the cannabinoids have a similar absorbance, and all of the acid forms do as well. Without a two color measurement, I’m not sure how useful it would be. It seems that the acid forms have at least 10x higher absorbance than non-acid forms, and finding LEDs in the range of 300-350nm doesn’t seem as simple.

What do you think? Can you see anything useful in this data that could be turned into an inexpensive measurement?

Also, if not LEDs, does anyone know of inexpensive broadband UV sources that might be useful with filters? Arc lamps seem to cost a fortune.


hmmm… nice paper, it has put all of the methods of testing cannabinoid potency, including TLC and HPLC… Spectrophotometry… Sounds tempting… But… They used cannabinoid isolates, not flower material… AFAIK it would be impossible to detect potency of each cannabinoid together from a flower sample… Maybe with some heavy, 11-dimensional topology mathematic formulas, i sure hope there is a formula… You would need UV spectrophotometer… They used this one:

Varian Cary 1e CARY1E Uv-visible Spectrophotometer System With Manuals for sale online | eBay

" A spectrophotometer is a color measurement device that is used to capture and evaluate color on just about anything, including liquids, plastics, paper, metal and fabrics." - Difference Between a Spectrometer and a Spectrophotometer | X-Rite Blog

There is a project for DIY spectrophotometer:

A Simple DIY Spectrophotometer : 8 Steps (with Pictures) - Instructables

but you would need uv spectra diffraction grating and a reliable UV source, or at least such a software that can account for spectre of UV lamp and some diy difrraction grate… Do you have any other resource about this method? Ill go for a hunt, ill report when i find something that can be of use to us… Peace…


Ill post here what i find, so that i dont spam the thread…

How plotting of data is done:

The Spectrophotometer: A demo and practice experiment - YouTube

Spectrophotometry Experiment - Full Explanation & Analysis by Mr Pauller - YouTube

Difference Spectrum–Deconvoluting a Mixture - YouTube

What is spectrophotometry

2.1.5: Spectrophotometry - Chemistry LibreTexts

Hmmm… It seems it should be possible to determine each cannabinoid in a mixture, but we would have to know measured extinction (absorption) coefficient on each wavelenght to have precise data… Something like its shown in 3. YT video, not just ext. coeff. at peaks… Quest goes on!

*edit nr. 2:

ok, i found an online tool to convert graph to number data:

WebPlotDigitizer - Extract data from plots, images, and maps (automeris.io)

i wont play with it yet, as it is morning christmas where i am, and i want to be with my family… but im definetly chasing this one!! if this works, only thing left to do is to make our own and test, test, test!!! <3 good job on finding this one mate! it may be of great usefulness to us…


edit nr. 3:

it seems there is a good diy solution for spectrophotometer found here:

(129) Building a Nanodrop Style UV/Vis Spectrometer - YouTube

but it measures only from 400nm… for anything below that, you need another sensor and special laser source, or deuterium bulb… im not giving up yet, but ill stop for today… ill report when i find something useful by the sunday… peace…

edit nr. 4:

couldnt rest, had to search for parts… so far, nothing useful… deuterium lamp is used as light source, which cost around 150$ to 200$ as for sensor, there are cameras that could pick >= 200nm wavelengths that cost around 500$… imo its better then to aim for cheap chinese uv/vis spectrophotometer, i inquired for some looking more professional, but it can be found for 2000 usd… if you buy your own lamp and camera, you need to account for spectrum curve of emitter and sensor, finished products have that accounted for… there are cameras with removed uv sensors, but i couldnt find any data on spectrum they detect… done as much as i could, hope youll have more luck… peace…


I tend to agree with @Wiener_Demeanor, great technical resource but I believe this would not be as straight forward in practice. You’d need to be able to de-correlate the response in some manner. Unfortunately, all of the different chemistries are responding across the same wavelength and with similar patterns. Since, for example, CBG, CBD, and THC have practically the same response, it would be difficult to tell the two apart using just a spectrometer. Perhaps you’d be able to detect presence but more difficult for individual quantity.

This is why we have HPLC and MS, they de-correlate chemistries by molecular weight such that there is a time component introduced. Different masses travel at different rates. At the end of sample, they do the spectral analysis.

Even more complicated systems exist that are able to differentiate isomers. These systems are able to differentiate chemistries that have the same mass but with slight differences in the molecular bonding.

So, if you dissolve the matter into a solvent and then measure the spectral response, you’ll get all of the present compounds measured all at once. Much of which will be overlapping. You’ll be able to differentiate between groups of compounds: (CBG, CBD, THC-9) vs (THC-A, CBD-A, CBG-A, CBN) with the note that you may be able to tease out CBN. It is also uncertain if any other compounds present in the solvent carrier will also absorb or fluoresce across similar wavelengths.

I think what you have here is something to provoke a thought exercise. Along with some other tools and procedures, you’ll have a technique to be able to detect individual chemistries. But, it may end-up looking like LC or MS in the end. The value ends-up determining a way to do this without using high pressure or high temperatures with complicated control systems. Or, how to do it cheaply but with accuracy. For instance, if one we’re able to strictly control sample temperature to some precision and then evacuate a vapor for analysis, you might be able to differentiate across different compounds with varying degrees of accuracy (this’ll look like a very simple MS).

But, but, but, trying it is always worth the experience and knowledge. Perhaps, we can decarb while realtime measuring the sample over a time span within the sample chamber. Maybe we can detect differences over time to sufficient precision, idk.


Well, total cannabinoids is still a valuable measurement IMO. I don’t think you’d necessarily need to have a detector for each one in order to have a useful piece of instrumentation.

The main problem I see is that the acid forms of cannabinoids have a much higher extinction than the non-acid. So they’ll provide too much of a difference in weighting a single measurement around 275nm. One idea I had was that a 2 color measurement, 1 at 275-280nm for a total and 1 around ~330nm for a measure of cannabinoid acids might plausibly be something that you could calibrate to give you a decent approximation of total cannabinoids.

I think if there’s any hope of making something inexpensive enough and chemical-free enough for a home grower/breeder to use, it would have to be an optical measurement, which is why I’m looking into this. TLC is feasible, but to me, the low cost and availability of the materials are not compelling compared to paying a lab to test samples.

I’m not sure convinced there’s anything compelling from the data, but I’m not discounting that there could be clever ways to make an optical measurement that would be meaningful… either in the chemistry of preparing a sample for measurement, or in the measurement itself.

Spectrometers are pricey, and UV light sources are as well. To use a prism or grating, you need to have focused or collimated light. It would be very hard to use a fluorescing source like a reptile lamp to do a spectroscopy measurement with that kind of broadband source. A UV prism would probably be very expensive as well. Most glass is not transparent toward UVC wavelengths.

Monochrome sources are optically easier to implement, but of course then we only get a single measurement instead of a spectrum, unless we added other colors of UV to the measurement as well.


Inexpensive? No. lol

I like the way you think though. There are people developing a device to use light to measure nutrition content in vegetables. This seems like a job a proper computer program and a pallet of money could definitely solve

I haven’t looked over the link yet but I’m pretty sure these are the people I’m talking about.
Addendum; Dan Kittredge is the dudes name, if you want to look him up on YouTube


That’s pretty sweet. I know that you can measure skin carotenoids using raman spectroscopy, and that it can tell you if you’ve been eating a lot of fruit. I wonder if that is something similar.


yea, reptile light bulbs and uv diffraction is a no go, i wrote that before i researched what this machine is and how you take measurements… i went into full adhd mode of researching how to make this device, not seeing until now it would be impossible to measure each cannabinoid separately… as i said, i was hoping for some exotic math to make this possible, like subtracting each of the graph from your spectrophotometer result, but that wont work, maybe it could be benefitial to see difference of extraction method and drying/curing times for total cannabinoid number… with only 2 diodes, you could use cheap arduino UV sensor and correct that with its sensitivity, altough, you would then need to make clear extract like you make with qwiso or something better not to have other plant material in your way… there is also this:

altough, you need 3 known samples… ill read the research paper to see if its meaningful for us…


Is production of cannabinoids in plants dependent on the wavelength? Would it follow those graphs? If so best production should be in the ~200-220 wavelength and in the ~260-280 range? iirc supplement I have seen was in the latter range.


were discussing measuring ammount of final product… for production, you would want to hit UVR8 protein… i dont have enough knowledge or data about it, and it isnt part of this subject…

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hmmm… tlc method with comparison of known substance seems doable… you would need to test extract in a lab, to get precise ammount of each cannabinoid… then have 3 different dilutions of it, and 1 you want to compare, as seen here:

then the result looks like this:

looks rather interesting… too bad you need mix of hexane and diethyl ether for clear test… even then, ive seen blobs of thc and cbd overlap… :confused: i have such need to test end products, i was really hoping for something good and cheap…


I share your need; fortunate to live in a legal area. So lab testing may be the answer for me today. In the future though, I much prefer self reliance.

I don’t understand 80% of this thread; just wanted to mention I too really am quite interested. Reading along and sounding out the words, good stuff boys.


btw there is this thing called tCheck, which measures total cannabinoid ammount of flowers and extract for 400usd, 3%± accuracy:

At Home Cannabis Potency Device | Thc & Cbd Potency Test | Weed Test Kit (tcheck.me)

which is also uv spectrophotometer, and it is cheap (so far UV sensor for >=200nm i found costed around 500 bucks, deuterium lamps for >=200 nm light source around 200 bucks)…

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right ROI should include at least some thought when time is an investment. :slight_smile: Exploring new stuff is nice and so is brainstorming and working toward a common goal.

was aware.


if no production nothing to measure…but leaving it there and the name is aptly chosen or living up to it?

Nice find! I wonder if that is a spectrophotometer or a monochrome absorption measurement. If a company can make money selling those at $300, I just think it must be simple like a 280nm UV LED and a photodetector.

It focuses the UV light sources through the oil and onto the detector

I was thinking of doing something fancier than that, using a differential amplifier between two cells to get better accuracy. Maybe I’ll try something simple first and just use a small quartz cuvette, a UV LED and photodetector.


hmmm, me like that… i cant wait to see what youll make!! watching you carefully :eyes: :heart_eyes:

hmmm i found this:

The spectrophotometric analysis of mixtures with overlapping absorption bands

i didnt read it, as ive moved on to another subject, but i know it must be possible to use spectrophotometry to measure even overlaping absorbance materials with some spicy math, many of handheld cannabinoid measuring devices use them… purl pro uses ir band to measure thc and cbd, maybe you can find a hint there… you can always use google scholar and sci hub to access other research materials for method of process of your data… peace…

Some additional reference material that might be useful for your research:

Fluorescence Spectroscopy in Biology Advanced Methods and their Applications to Membranes, Proteins, DNA, and Cells (Springer Series on Fluorescence) ( PDFDrive ).pdf (3.5 MB)
Fluorescence of cannabinoids dionyssiou-asteriou1975.pdf (272.6 KB)

Chemical fingerprinting of single glandular trichomes of Cannabis sativa by Coherent anti-Stokes Raman scattering (CARS) microscopy_s12870-018-1481-4.pdf (2.5 MB)
ORIGINAL PAPERDirect detection ofΔ9-tetrahydrocannabinol in aqueoussamples_tan2010.pdf (261.0 KB)
Ultraviolet absorption and luminescence properties of some cannabis constituents_bowd1971.pdf (448.1 KB)
Raman Spectroscopy Study of Delta-9-Tetrahydrocannabinol and Cann.pdf (3.4 MB)


Funny enough, I have a few raman spectrometers of my own. One day, while looking at surplus lab equipment, I found a lot of devices. They were used as skin carotenoid detectors. Looking at the pictures, I realized they were probably raman spectrometers.

For $20 a pop, I scored a few of them. They came in a bare metal frame with 5mW fiber pigtail 405nm lasers, low noise power supplies, USB spectrometers and notch filters. I never set it up, because the absorption seems to be almost non-existent… but maybe I should give it a try. That fluorescence was done with a 395nm light.