Test For UVc Light, Verification of Wavelength

Thread Starter

MrAl

Joined Jun 17, 2014
7,666
Hello there,

A question came up as to whether or not a UVc light 'bulb' i have is really UVc or some other UV grade. The 'bulb' says on the side, "UV Germicidal Lamp".
Now i know that sounds good, but wavelengths other than 265nm also kill some germs but to get more of them you really need 265 or thereabouts, or shorter (180nm for example). UV also covers 405nm but hat's not as effective.

So i was thinking of a way to test this light. If it was a tube i might not think about it as much but it is made of a lot of LEDs that are supposed to be UVc LEDs. When i look all over the web i cant find one UVc LED that looks like these though. A test would tell me right away.

Now from what i understand, the forward voltage of a 265nm is quite a bit higher than for a 406nm LED. The voltage is around 7v with a 5v minimum for lower current, and for 405nm it could be as low as 3v to maybe 5v as a maximum.
So UVc 265nm has roughly 5v to 7v or so, while the 405nm has roughly 3v to 5v. That is enough to measure.
However, measuring the voltage is not that easy because of the mounting of the SMD parts, which would either require soldering to the ends of the LED or trying to hold two probes on the bulb while someone else turns it on.
Either of which i dont want to do.

So i looked into this, and you can buy 'cards' that test for UV light, but i think the ones that test for UVc are quite a bit expensive while the regular UV ones are only around 9 dollars USD. Looking up a few other things like UV activated epoxy, i found that the epoxy hardens with a lower frequency light (longer wavelength like 400nm) and it should not react much to 265nm.
So, putting a dab of the epoxy on a stick and holding up to the 60watt LED 'bulb' and turning it on with eyes blocked completely, i exposed the dab of epoxy for about 10 seconds. Amazingly, it did not harden or even seem to change consistancy. To be sure, i then exposed the dab to a UV light that normally is used to harden the epoxy in around 3 seconds. Holding the light above the dab, it harden rock hard leaving it exposed for about 5 seconds.

So what do you think. You think this is a good enough test? I suppose the light wavelength could be longer than 405nm but then i would think it would be a total fake, and might appear too visible. However, the lamp does appear to be a bight blue white color when turned on.
Also, when i price the UVc LEDs on the web they run 8 to 12 dollars USD or more, while the 405nm LEDs are only about 2 dollars USD, and i only paid 35 dollars for one of these bulbs and they have at least 100 LEDs on the sides and bottom.

So you think that was a good enough test or do you know of a cheap reliable UVc measuring card or device?
 

jpanhalt

Joined Jan 18, 2008
9,718
Simple. All you need is a fluorescent dye that is excited at 200 nm or lower and has a Stokes shift of at least 200 nm or greater. Or, put it though a monochrometer and do photon counting on the output.
 

Papabravo

Joined Feb 24, 2006
13,926
Hello there,

A question came up as to whether or not a UVc light 'bulb' i have is really UVc or some other UV grade. The 'bulb' says on the side, "UV Germicidal Lamp".
Now i know that sounds good, but wavelengths other than 265nm also kill some germs but to get more of them you really need 265 or thereabouts, or shorter (180nm for example). UV also covers 405nm but hat's not as effective.

So i was thinking of a way to test this light. If it was a tube i might not think about it as much but it is made of a lot of LEDs that are supposed to be UVc LEDs. When i look all over the web i cant find one UVc LED that looks like these though. A test would tell me right away.

Now from what i understand, the forward voltage of a 265nm is quite a bit higher than for a 406nm LED. The voltage is around 7v with a 5v minimum for lower current, and for 405nm it could be as low as 3v to maybe 5v as a maximum.
So UVc 265nm has roughly 5v to 7v or so, while the 405nm has roughly 3v to 5v. That is enough to measure.
However, measuring the voltage is not that easy because of the mounting of the SMD parts, which would either require soldering to the ends of the LED or trying to hold two probes on the bulb while someone else turns it on.
Either of which i dont want to do.

So i looked into this, and you can buy 'cards' that test for UV light, but i think the ones that test for UVc are quite a bit expensive while the regular UV ones are only around 9 dollars USD. Looking up a few other things like UV activated epoxy, i found that the epoxy hardens with a lower frequency light (longer wavelength like 400nm) and it should not react much to 265nm.
So, putting a dab of the epoxy on a stick and holding up to the 60watt LED 'bulb' and turning it on with eyes blocked completely, i exposed the dab of epoxy for about 10 seconds. Amazingly, it did not harden or even seem to change consistancy. To be sure, i then exposed the dab to a UV light that normally is used to harden the epoxy in around 3 seconds. Holding the light above the dab, it harden rock hard leaving it exposed for about 5 seconds.

So what do you think. You think this is a good enough test? I suppose the light wavelength could be longer than 405nm but then i would think it would be a total fake, and might appear too visible. However, the lamp does appear to be a bight blue white color when turned on.
Also, when i price the UVc LEDs on the web they run 8 to 12 dollars USD or more, while the 405nm LEDs are only about 2 dollars USD, and i only paid 35 dollars for one of these bulbs and they have at least 100 LEDs on the sides and bottom.

So you think that was a good enough test or do you know of a cheap reliable UVc measuring card or device?
Do you have enough spare change for a UV spectrograph?
 

Thread Starter

MrAl

Joined Jun 17, 2014
7,666
Hello,

Well i did not want to spend much money because it will be a one time use.
1000 USD+ is out of the question, but even 100 USD is more than i wanted to spend, same reason.
I saw tests cards for 8 bucks but they dont do UVc. If i could find one that did UVc i might get one.

But John you said that there was a special dye i could use so i guess you have faith in a chemical test. I think the UV activated epoxy/glue test was somewhat conclusive then. I'd still like another test though to back that up.
The glue cures with a 395nm source, and the 'bulb' that is supposed to be 265nm did not cure it even after 3 times longer than is needed with the correct 395nm source.
 

jpanhalt

Joined Jan 18, 2008
9,718
I didn't say there was such a dye; I suggested that if you could find one as described, you could use it. Maybe the makers of the 200 nm sources have a solution to the problem.

You have said that 200 nm light is far less damaging to humans than 254 nm light is. If that is the case by whatever mechanism, I suspect it will not be very effective with the resins you mention. Of course, if the 200 nm lamp also emits longer wavelength light, that light could be the catalyst and also damaging to you. If you can see that the lamps are even on, then they also produce visible light.
 

Janis59

Joined Aug 21, 2017
1,187
Take a piece of crushed kinescope type TV screen (front part), it is well fluorescent at high energy excitation.
 

jpanhalt

Joined Jan 18, 2008
9,718
The problem is not finding something that is fluorescent/phosphorescent with short wavelength excitation, but in finding something that does not emit light when excited with longer wavelengths too. MrAl wants to know how much light is produced at 200 nm.

From Wikipedia (https://en.wikipedia.org/wiki/Mercury-vapor_lamp )
In low-pressure mercury-vapor lamps only the lines at 184 nm and 254 nm are present. Fused silica is used in the manufacturing to keep the 184 nm light from being absorbed. In medium-pressure mercury-vapor lamps, the lines from 200–600 nm are present. <snip> Low-pressure mercury-vapor lamps usually have a quartz bulb in order to allow the transmission of short wavelength light. If synthetic quartz is used, then the transparency of the quartz is increased further and an emission line at 185 nm is observed also. Such a lamp can then be used for ultraviolet germicidal irradiation. The 185 nm line will create ozone in an oxygen containing atmosphere, which helps in the cleaning process, but is also a health hazard.
Emission by low-pressure mercury sources is mostly at 254 nm (https://www.tandfonline.com/doi/abs/10.1080/01919510802341012?scroll=top&needAccess=true&journalCode=bose20#:~:text=The efficiency (conversion of electrical,approximately 10% at 185 nm. ):
The efficiency (conversion of electrical energy into UV-emission) of the low pressure mercury discharge itself (not lamp!) is rather high: approximately 35–40% at the wavelength of 254 nm and approximately 10% at 185 nm.
When one considers practical aspects, including loses from absorption by the envelope, air, and solvents/suspending matrix, we considered such lamps in fused silica or quartz envelops to be relatively pure 254 nm. There are other technologies, of course.
 

Thread Starter

MrAl

Joined Jun 17, 2014
7,666
Yes a regular fluorescent lamp tube will fluoresce with a UV light source but probably has too wide of a bandwidth to be able to detect just one narrow band or just lower than say 280nm.
The wave lengths i need to detect are around 275nm or lower. 320nm is probably getting too high.
 
Last edited:

KMoffett

Joined Dec 19, 2007
2,883
We have a mineral display in the Geology Department at a local college. It's lit sequentially by white light, 356nm, and 254nm UV bulbs. Some minerals fluoresce at one wavelength and not at the other. Several are really strong at 254nm. If there is a College or University near you they might be able to help you determine if you have UVc output.
 

Marc Sugrue

Joined Jan 19, 2018
133
Hello there,

A question came up as to whether or not a UVc light 'bulb' i have is really UVc or some other UV grade. The 'bulb' says on the side, "UV Germicidal Lamp".
Now i know that sounds good, but wavelengths other than 265nm also kill some germs but to get more of them you really need 265 or thereabouts, or shorter (180nm for example). UV also covers 405nm but hat's not as effective.

So i was thinking of a way to test this light. If it was a tube i might not think about it as much but it is made of a lot of LEDs that are supposed to be UVc LEDs. When i look all over the web i cant find one UVc LED that looks like these though. A test would tell me right away.

Now from what i understand, the forward voltage of a 265nm is quite a bit higher than for a 406nm LED. The voltage is around 7v with a 5v minimum for lower current, and for 405nm it could be as low as 3v to maybe 5v as a maximum.
So UVc 265nm has roughly 5v to 7v or so, while the 405nm has roughly 3v to 5v. That is enough to measure.
However, measuring the voltage is not that easy because of the mounting of the SMD parts, which would either require soldering to the ends of the LED or trying to hold two probes on the bulb while someone else turns it on.
Either of which i dont want to do.

So i looked into this, and you can buy 'cards' that test for UV light, but i think the ones that test for UVc are quite a bit expensive while the regular UV ones are only around 9 dollars USD. Looking up a few other things like UV activated epoxy, i found that the epoxy hardens with a lower frequency light (longer wavelength like 400nm) and it should not react much to 265nm.
So, putting a dab of the epoxy on a stick and holding up to the 60watt LED 'bulb' and turning it on with eyes blocked completely, i exposed the dab of epoxy for about 10 seconds. Amazingly, it did not harden or even seem to change consistancy. To be sure, i then exposed the dab to a UV light that normally is used to harden the epoxy in around 3 seconds. Holding the light above the dab, it harden rock hard leaving it exposed for about 5 seconds.

So what do you think. You think this is a good enough test? I suppose the light wavelength could be longer than 405nm but then i would think it would be a total fake, and might appear too visible. However, the lamp does appear to be a bight blue white color when turned on.
Also, when i price the UVc LEDs on the web they run 8 to 12 dollars USD or more, while the 405nm LEDs are only about 2 dollars USD, and i only paid 35 dollars for one of these bulbs and they have at least 100 LEDs on the sides and bottom.

So you think that was a good enough test or do you know of a cheap reliable UVc measuring card or device?
Be careful with UV & Especially UVC it can damage your eyes and burn your skin if viewed directly
 
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