Important info for new Solarmeter 6.5 owners

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Re: Important info for new Solarmeter 6.5 owners

Postby Taterbug » Mon Jun 19, 2017 5:52 am

I'm not sure if Fran gets notified on this thread or not, hopefully she does cause she is way better at explaining the nuances than I am. ( http://www.uvguide.co.uk/usinguvmeter.htm )

In short though a big part of why she recommends the 6.5 is that most people are looking for one device to use, "simple arithmetic" can be inconvenient or confusing to have to manage and that for most users total flux isn't very meaningful. Sticking with a trusted band and measuring output is going to be a lot easier for many folks. Having multiple devices is great if you really want to analize the performance and quality of the lights, but at $250 a pop not many people have the resources.

As described, UVI is weighted based on the photo-biologically active portion of the spectrum, so it is good for judging the effectiveness of trusted lamps. Just know how much total radiation you are seeing doesn't tell much about how useful it is to the body.
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Re: Important info for new Solarmeter 6.5 owners

Postby lilacdragon » Mon Jun 19, 2017 7:04 am

Hi, KingofNobbys. ( Hi, Taterbug ;) )

King of Nobbys, I'm afraid I have to contradict you here, because although you clearly have a detailed understanding of the way in which the UV Index was devised, using a spectrometer which of course responds to, and integrates the UVA + UVB +UVC, the broadband UV Index meter works in an entirely different way. It is simply a SiC photocell responding to the wavelengths which reach it through a rather costly filter cap which selectively blocks out all UVA and most UVB above 315nm. Its sensitivity response can be seen here: http://www.solarmeter.com/media/wysiwyg/model65response1.gif
This curve approximates the erythemal response (hence its use as a UV Index meter) but it is also very similar to the action spectrum for vitamin D3 synthesis - it is a >90% match in the UVB wavelengths.
This is what makes the readings from this meter a very good proxy for the ability of a light source to synthesise vitamin D3 - the best one, in fact, that I've ever found apart from a spectrometer, which is of course an extremely impractical tool for a hobbyist!
And yes, the UV Index is a very easy scale to understand, which is why we adopted it for the Ferguson Zone system (see http://www.reptilesmagazine.com/An-In-Depth-Look-At-UV-Light-And-Its-Proper-Use-With-Reptiles/
I also own a Solarmeter 5.7 UVA+UVB meter, but I don't find it useful, for one reason - its sensitivity response curve: http://www.solarmeter.com/media/wysiwyg/Solarmeter_Model_5.7_Graph_2.pngIt is only about 50% as sensitive to UVB as to UVA. This isn't such a problem with a spectrum close to sunlight, in which UVB is only a small fraction of the total UVA+UVB, so its under-estimation is not so critical. But most of our lamps have a higher percentage of their output in the UVB range; so this meter is likely to underestimate, possibly seriously, the amount of UVB present. I've seriously considered fitting a filter to block all UVB, so it can act as a purely UVA meter; but there are no filters with a perfect 320nm cut-off, so that means I'd need to calibrate it myself, which I don't have the means to do. So a bit pointless :)
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Re: Important info for new Solarmeter 6.5 owners

Postby kingofnobbys » Wed Jun 21, 2017 1:47 am

lilacdragon wrote:Hi, KingofNobbys. ( Hi, Taterbug ;) )

King of Nobbys, I'm afraid I have to contradict you here, because although you clearly have a detailed understanding of the way in which the UV Index was devised, using a spectrometer which of course responds to, and integrates the UVA + UVB +UVC, the broadband UV Index meter works in an entirely different way. It is simply a SiC photocell responding to the wavelengths which reach it through a rather costly filter cap which selectively blocks out all UVA and most UVB above 315nm. Its sensitivity response can be seen here: http://www.solarmeter.com/media/wysiwyg/model65response1.gif
This curve approximates the erythemal response (hence its use as a UV Index meter) but it is also very similar to the action spectrum for vitamin D3 synthesis - it is a >90% match in the UVB wavelengths.
This is what makes the readings from this meter a very good proxy for the ability of a light source to synthesise vitamin D3 - the best one, in fact, that I've ever found apart from a spectrometer, which is of course an extremely impractical tool for a hobbyist!
And yes, the UV Index is a very easy scale to understand, which is why we adopted it for the Ferguson Zone system (see http://www.reptilesmagazine.com/An-In-Depth-Look-At-UV-Light-And-Its-Proper-Use-With-Reptiles/
<<< I hadn't seen this report but had seen other detailed studies done in the UK , which this report is based on. Interesting read nonetheless so ta to you.
I also own a Solarmeter 5.7 UVA+UVB meter, but I don't find it useful, for one reason - its sensitivity response curve: http://www.solarmeter.com/media/wysiwyg/Solarmeter_Model_5.7_Graph_2.pngIt is only about 50% as sensitive to UVB as to UVA. This isn't such a problem with a spectrum close to sunlight, in which UVB is only a small fraction of the total UVA+UVB, so its under-estimation is not so critical. But most of our lamps have a higher percentage of their output in the UVB range; so this meter is likely to underestimate, possibly seriously, the amount of UVB present. I've seriously considered fitting a filter to block all UVB, so it can act as a purely UVA meter; but there are no filters with a perfect 320nm cut-off

<<< actually there are suitable filters
Long Pass Filters
LP Cutoff 320nm see https://www.newport.com/p/5CGA-320
LP Cutoff 400nm see https://www.newport.com/p/5CGA-400
Short Pass Filters
SP Cutoff 400nm see https://www.newport.com/p/05SWF-400-B

, so that means I'd need to calibrate it myself, which I don't have the means to do. So a bit pointless :)


Yes. I was trying to avoid being very technical .... keeping the physics minimal , mostly because few keepers will follow the detailed physics and associated calculus.

I personally prefer an actual measurement of the UVB flux , IMO it's a superior approach to trying to infer something meaningful from the UVI to get an estimate of UVB performance (of a globe or tube)..

As stated, it's a matter of the keeper's choice.
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Re: Important info for new Solarmeter 6.5 owners

Postby lilacdragon » Wed Jun 21, 2017 4:50 am

Those interference filters are very nice (thanks for the link :) ) but they do not have sharp enough cut-off to eliminate (for example) a UVB response from a UVB+UVA broadband meter.
For example, the specs for the CGA-320:
"Cut-on Wavelength at 50% Absolute Transmittance 320 ± 5 nm
Cut-on Wavelength at 90% Absolute Transmittance ≤340 nm
Cut-on Wavelength at OD5 ≥300 nm"
That means there is transmission from 300nm upwards, and 50% gets through at 320nm; only 90% gets through at 340nm! So that means it would still be necessary to re-calibrate a UVB+UVA meter if you wanted to convert it to a UVA-only meter.
With both meters ( 6.2 and 5.7 ) , it is simple arithmetic to get the microwatts UVA / sq-cm from the readings from the model 5.7 ( UVA + UVB) MINUS the readings from model 6.2 (UVB) = UVA.

Unfortunately, this won't give you anything resembling an accurate readout unless you happen to be measuring the irradiation from a specific type of low-UVB human tanning lamp (to which both meters are calibrated).
This is because neither of these broadband meters have "clean" cut-off; both have tail-offs into out-of-bandwidth wavelengths. The 6.2 meter responds to UVA up to around 335nm (as well as all UVB and some long-wavelength UVC). The 5.7 meter only responds to UVB with about 50% of the response it has to an equivalent UVA irradiance. So the reading from a reptile UVB lamp, with a 6.2 meter, is idiosyncratic (depends on how much UVA the lamp emits) - which is one reason I don't rely on mine for checking lamp safety any more. And the reading from the 5.7 vastly under-estimates the UVB, so if you subtract the 6.2 reading from the 5.7 reading, it's anybody's guess as to whether your reading is approaching the truth... :(
The other problem with relying upon total UVB (µW/cm²) is a serious one. (see: http://www.uvguide.co.uk/phototherapyphosphor-tests.htm#photoactivity )
Because biological responses to UV are wavelength-dependent, with shorter wavelengths being much more hazardous, it does not help knowing the total UVB, if you don't know what percentage of this is in the shorter, more hazardous wavelengths.
Some cheap Chinese lamps are still around with a great deal of short-wavelength UVB, bordering on UVC. This type of lamp can do serious damage at irradiances of as little as 50µW/cm² - which is a really, really safe, very low irradiance if the spectrum is like ordinary sunlight.

Yes of course, it is the keeper's choice as to what meters (if any) you choose. As long as the spectrum of the lamps you choose is known to be sunlike, a Solarmeter 6.2 will do good service.
Nothing's perfect. But the UV Index meter only responds to shorter wavelengths, so it is a better instrument for detecting possibly hazardous irradiation levels. That's why I use mine for day-to-day work, and out in the field.
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Re: Important info for new Solarmeter 6.5 owners

Postby Jcarey » Wed Oct 04, 2017 7:32 am

I'm looking to rent a Solarmeter for one time use. I have searched the internet high and low and can't find a source. Well, did find one rental source... the manufacturer of the Solarmeter. They have a rental program but unfortunately they no longer rent the 6.5.
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