Detecting UV marks using a UV sensor

How can i detect from a distance of 1-2cm, in a low light environment, a line drawn on paper by a UV marker such as the following UV markers:

  1. ... _s/108.htm ... 2749.l2649

What UV sensor should i use? Do UV sensors have an internal UV LED or would i need to add a LED that lights the paper? If i need to add a LED, what kind of LED should i use?


I am confused! Are you wanting to detect UV light or visible light when something is excited by UV light?


Any visible light camera will work to detect the lines, when they are illuminated by UV light.

1 Like

How can i detect from a distance of 1-2cm, in a low light environment, a line drawn on paper by a UV marker

If the background "white" is rather uniform, you "may" be able to get by with something like this:

UV LEDs are not all uniform, different wavelengths will cause the dyes to produce different intensities as well different UV intensities. Getting a project calibrated may be more hit-n-miss.

Investing in a Raspberry Pi and camera running AI may be more reliable as the system is trainable:

I want to find the simplest analog output sensor, that can detect the UV mark, when iluminated by UV light.

Please be more forthcoming with the environment you are suggesting. Dark room? Normally light room? Outside at night? Outside in sunlight? You just mention low light, but what does that mean? Your low light is not my low light,
Have you tested any sensors for your project?


Test several and choose the simplest that actually works under a variety of conditions. We can't do that for you.

Your choices for analog are only a photo diode or a photo-multiplier tube. Are you willing to make the required lens system or the parabolic mirror?

Yes, i found out today by testing, that a photo-transistor is able to detect the difference, between a UV marker line reflection over paper, when a UV LED is pointed at the UV marker line and a blank area on the paper, that the UV LED is pointing at, where there is no UV mark.

You can see it with your eyes, its not UV!

Fluorescent dyes emit visible light when lit with UV light, so you only have to detect visible light. But you do need to illuminate it with UV light. Some fluorescent dyes work even with blue light in fact, and these will appear coloured under normal light.

Fluorescent dyes invisible in normal light are often used to secretly mark objects, which I think is the application here?

Note that the actual wavelength of UV light needed varies between dyes, and that the harder UV wavelengths require precautions to be taken as they can harm your eyes and skin.

Thanks, yes, it took me some time to discover that what you describe about detecting the UV markers, in the visible spectrum, is correct.

BTW, i suspect that a red UV marker i got only a few days ago, reflects UV light into the visible spectrum, even stronger than the blue and yellow UV markers i have, but i still need to make the temt6000 sensor measurments, to be sure about it.

Its not reflection, that's different! Fluorescence is when the (typically blue or UV) light is absorbed and converted into chemical energy, then later the chemical energy is released as light of a different (longer) wavelength. 'Later' can be anything from picoseconds to millions of years depending on the material involved.

1 Like

The temt6000 coupled to a UV LED, differentiates a paper with a flourescent marker line (3mm thick) and a blank paper with no line on it, by a value of only 30-40 out of 1024 AtoD conversion.

This small difference results in too many situations of false poitive and false negative.

Is there another LUX sensor model, that is simple to use with an Arduino and can give a better result or are there any code changes, that can be done for that purpose?

It seems that a difference of at least 150 (out of 1024) is required.

As an example of a good difference i will describe the following:

In detecting black lines, using an IR sensor, as in line tracker robot projects, the difference of sensing results, between a black line drawn on the paper and a blank area on the paper, goes up all the way to a value of 700 out of 1024 !!

To increase the signal to noise ratio, reduce the noise. You need very good color filters to remove the irrelevant background light.

Another approach is to use modulated UV light and detect only a modulated fluorescence emission of the appropriate wavelength.

Where can such a filter be found and how do i apply it on a temt6000 sensor?

Edmund Scientific, among many others, sells narrow bandwidth color filters. Of course you have to know what wavelength range is appropriate, and they aren't cheap.

What about the modulation approach? How is it implemented on the UV LED side and on the sensor side?

You could use PWM to switch the UV LED on and off at around 38 kHz (typical of IR remote controls), and use a bandpass filter with a photodiode and color filter to detect fluorescence emission at 38 kHz.

Expensive components are a problem in this case (regarding the filters at Edmund Scientific).

Detecting weak signals amid background is always expensive, unless you can take advantage of some large scale consumer technology.