Thursday, January 19, 2017

Solarmeter Model 6.2 Sensitive UVB Meter

Solarmeter Model 6.2 Sensitive UVB Meter


Compact, Handheld, and Durable

Simple Single-Button Operation

NIST Traceable Accuracy

LCD Display

Made In USA


Monitoring Reptile Lamp Intensity and Aging (Peak sensitivity is 295nm, the point required  to induce Vitamin D3 synthesis.)

Monitoring UV Lamp Intensity & Aging

Testing Acrylic Shield Transmission

Testing Eyewear UV Block Capabilities

Measuring Outdoor Shady Area UVB

Testing Window Film / Tint Transmission

Choose Sensitive Model 6.2 For Indoor / Low Intensity Applications

Choose Standard Model 6.0 For Outdoor / High Intensity Applications

Fig.1 shows the range of UVB meters we use in all our tests. These meters are easy to use and we have found the readings to be consistent and reliable. The UVB meters are of two types: the "UVB Meter" which measures the total UVB across the entire wavelength range (280 - 320nm) in microwatts per square centimetre (µW/cm²), and the "UV Index Meter" which gives a reading with greater sensitivity to the shorter UVB wavelengths, responsible for vitamin D3 synthesis in the skin.

The UVB meters are sold by Solartech under the brand name Solarmeter 6.2, and by ZooMed under their own label as the ZooMed Digital UVB Radiometer. (These models are identical apart from their branding.)

The UV Index meters are sold by Solartech as the Solarmeter 6.5, and by ZooMed as the ZooMed Digital UV Index Radiometer. (These models are also identical apart from their branding.)

To make life a lot simpler, the meters will simply be referred to as "Solarmeter 6.2" or "Solarmeter 6.5" in the following discussion.

A little more detail...

The Solarmeter Model 6.2 UVB /ZooMed Digital UVB Radiometer

The Solarmeter 6.2 UVB meter, designed and made by Solartech, Inc. was the first meter ever sold to reptile keepers that was reasonably accurate, yet still affordable. ( 
This meter was used in all our earlier tests, and is still claimed to be the most accurate hand held UVB meter on the market. This very instrument has been used in research into vitamin D3 synthesis at the Vitamin D, Skin and Bone Laboratory at Boston University Medical Center 19 and in numerous other research projects worldwide.
This meter estimates the total UVB radiation falling on its sensor (it responds to wavelengths from UVC right up to and including a little short-wavelength UVA at about 330nm). It has very high precision - 1µW/cm² - so it is extremely useful for the monitoring of decay in any one lamp, and in measuring very low levels of UVB both in the field and in the vivarium.

Its broadband response (typical of all UVB meters) to the entire UVB waveband, however, causes a problem if we want to compare the ability of different lamp brands to enable vitamin D3 synthesis, or to match up sunlight and lamp UV levels. Solar Vitamin D3 synthesis almost all occurs between 290 - 315nm, but the shorter the wavelength, even within this small range, the greater the effect. 
In theory, if one lamp had most of its UVB in the shorter wavelengths, e.g., below 305nm, whereas another had most of its UVB in the longer wavelengths, e.g., above 315nm, they could both give identical readings with a Solarmeter 6.2, but the first lamp would be much better at producing vitamin D3 than the second one.... it might even have unwanted UVB from below 290nm or even UVC, and cause skin or eye damage....... 
This is also why UVB readings from natural sunlight cannot be used as guides to "suitable" readings from a lamp in a vivarium. Natural sunlight has a far greater proportion of its UVB in the longer wavelengths. Most reptile UVB lamps have the exact opposite to this, with a higher percentage of their UVB in the more photo-reactive, shorter wavelengths. To put it crudely, their UVB is "stronger". This problem was highlighted when in 2006-7, certain fluorescent lamps with quite low UVB readings caused eye and skin damage in many reptiles 4. These lamps emitted extremely short-wavelength UVB; only small doses of radiation from these lamps could burn living skin very quickly.

For these reasons, a few years ago several researchers started looking away from broadband UVB meters and concentrating on finding something to measure just the wavelengths responsible for vitamin D3 synthesis (and, in excess, cause harm to skin and eyes). A spectrometer is ideal for laboratory work, but extremely unlikely to be available to reptile keepers or herpetologists out in the field.... a handheld meter was still needed....
Fortunately for us, Solartech had launched the Solarmeter 6.5 UV Index meter.

The Solarmeter Model 6.5 UV Index Meter/ZooMed Digital UV Index Radiometer

The UV Index meter created by Solartech ( performed extremely well in comparison trials with other UVI meters and a research-grade spectrometer 72.

The UV Index (UVI) is an internationally-recognised, unitless measurement of the intensity of the photoreactive part of the spectrum of sunlight (or any light containing ultraviolet). It is often included in weather forecasts. It is based upon an integration of the spectrum of the sunlight (or lamp) with the action spectrum for human erythema, ie., sunburning 73. 
Of course this is totally irrelevent for reptiles and amphibians! ...but that action spectrum is very close to the action spectrum for vitamin D3 synthesis, which of course we ARE interested in. It's not a perfect overlap, but interestingly, the response curve of the Solarmeter 6.5 meter appears to follow the D3 action spectrum even more closely than it does the erythema action spectrum. It provides a good enough match, in fact, for the readings from Solarmeters with this sensor/filter combination to act as a proxy for the vitamin D3-producing ability of the light source 74.

The match is very good indeed. We have calculated that the 6.5 meter's sensor response from two different years of manufacture (when inevitable differences between batches of sensors/ filters occur) were 96.0% and 93.2% matches, respectively, to the CIE pre-vitamin D3 spectrum from 290 - 400nm. This is impressive for a relatively inexpensive instrument. What this means is that although Solarmeter 6.5 UV Index meters are still broadband meters with, of course, the previously described disadvantages still applicable, the very specific sensitivity response negates most of their effects. Hand-held meters can never be "accurate" in the same way that a spectrometer can be. From a practical point of view, however, we believe that a Solarmeter 6.5 is more than adequate for matching the output of a lamp with a known, safe spectrum with that of sunlight, when setting up a UV gradient in a vivarium indoors.

New recommendations for suitable UVB gradients in vivaria are being developed based upon field studies recording the UV Index in the microhabitat of numerous species in the wild. The pioneering work in this field was done by Dr. Gary Ferguson and his research team from Texas Christian University 75. This paper has been used as the basis for establishing what have been named the "Ferguson Zones" - a simple division of reptile and amphibian species into 4 "Zones" or "UVI ranges" based upon their basking behaviours and microhabitat, which together determine their daily UV exposure. 
The Ferguson Zones have been used by the British and Irish Association of Zoos and Aquaria's Reptile and Amphibian Working Group's UV guide, now published in the Journal of Zoo and Aquarium Research 76 and have been added to the labelling and the instruction leaflet for the ZooMed UV Index meter 77. They are also appearing on some manufacturer's instructions for UV lighting products.

Each of our new lamp test result files (coming soon) will contain a page with a simple guide to the Ferguson Zones.

Measuring UVB with the UVB and UVI meters

The meter is small, fitting easily in one hand, and is powered by an ordinary 9v battery. The sensor is at the top of the meter, and to take a reading, the operator simply aims the meter directly at the UV source and presses a button on the front of the unit. The amount of UV reaching the sensor at that moment is displayed on the LCD panel. 
In the case of the Solarmeter 6.2, the readout is in microwatts per square centimetre (uW/cm²). If, for example, the reading was 023 uW/cm², this would mean that a square centimetre of reptile skin would be getting 23 microwatts of UVB at that point.
The Solarmeter 6.5 readings are of the unitless UV Index scale. If, for example, the reading was 03.5, this means that the reptile skin would be getting UVI 3.5 at that point.

The sensor is extremely sensitive, with minute changes in the angle between sensor and source causing variations in the readings. Logically, the highest readings will be seen when the sensor is most accurately aligned in the beam of light; when taking hand-held recordings, it is adviseable to "scan" for the best alignment with very slow, very small movements. With practice, lining up the sensor can be done fairly quickly and very accurately. When taking recordings, we always use the highest readings obtained consistently (i.e. on at least 2 to 3 "scans") on each occasion.

What we have been able to do, with our hand-held radiometers, is to look at the UV output of the sun, and of any light source, and investigate in detail the initial output of a new lamp; the decay in the output of a lamp with time; and the characteristics of the UV "beam" for each type of lamp - how far the UVB light extends from the lamp and in what directions. 

Between us we have taken many thousands of readings both outdoors in natural sunlight and shade, and indoors from a wide range of UV products. 

There's more detail about our project, the accuracy of our readings and comparisons with other work in this field in the Introduction to the Lighting Survey  (coming soon)

The sections below describe the methods of recording we have found the most useful when using the meter outdoors (for solar recording), indoors in the vivarium, and on a simple "test bench".

The page concludes with a short section on comparing different UVB meters, and a discussion of one or two problems which might be encountered when using the Solarmeters, along with their solutions.

Solar Recordings

The readings collected for our studies on UV light in nature are mainly direct readings, for which the meter is aimed directly at the sun. These give a picture of the maximum UV which a reptile could obtain if it was fully exposed to sunshine at that location. (However, it's important to remember that most wild reptiles only bask in full sun for any length of time in the early morning, when the UV is not very strong.)

When taking solar recordings, never look directly at the sun. It is easiest to align the meter whilst facing the sun. Hold the meter out at a comfortable distance at just below shoulder level and "scan" carefully by tipping the meter towards the sun, searching for the highest reading.

Fig.3:  Direct Solar RecordingReadings need to be taken out in the open, where trees or buildings do not block a clear view of the sky. The sensor's field of view is a full 180° with a cosine response curve - this means that although it is most sensitive to whatever is directly in line with it (in this case, the sun), it will include diffused UVB from the sky around the sun in the reading. If this "sky" includes the dark silhouette of a building or tree, a lower reading will be obtained. Conversely, if there are large reflective surfaces such as water or snow beneath the sky, reflected and scattered UV from these may result in a higher meter reading.

Close to sunrise and sunset, readings from the sky above the sun may be slightly higher than those from the sun itself. This is because light from closer to the horizon must pass through a thicker layer of atmosphere. Water vapour in the air scatters light of shorter wavelengths more strongly than longer wavelengths; close to the horizon this thicker layer scatters enough short-wavelength light to remove most of the ultraviolet and blue. (This is why, of course, the rising or setting sun appears only red or orange.)

If taking a series of readings throughout a single day, ideally all the readings should be taken from the same spot, so that the readings are comparable one with another. It is also important to record the exact time of each recording. As the sun rises in the sky, the reduction in the thickness of atmosphere through which the light is passing causes an extremely rapid increase in UVB. We have recorded changes of a microwatt a minute. For example, between 7.30am and 8am on June 10th 2005, in Wales, UK, under a clear sky, the reading climbed from 40 to 70uW/cm². By 8.30am it was 105uW/cm² and by 9am it was 135uW/cm².

When taking solar recordings, it's useful to note the weather conditions; in particular, if the sun is shining, is it in a clear, deep blue sky or is there high cloud or haze? The increase in water vapour in the sky due to these will reduce the UVB levels reaching the ground.

If there is total cloud cover, direct solar recordings may not be possible. So-called "global" recordings usually give the highest readings with 100% overcast skies. To obtain these, the meter is held vertically, to record from the zenith (directly above the observer).

When recording for a database, you may also wish to record the location (latitude and altitude) at which the recording was made. If your country is using Daylight Saving Time this too needs adding to your report; and remember, if so, the sun will reach its highest point in the sky, and UVB its maximum level, around 1.00pm Local Time rather than at noon.

Fig.4 shows recordings made with a Solarmeter 6.2 during the course of one clear day in August in Wales, UK. Faint high cloud and haze in front of the sun has caused slight "dips" in the graph at various times but the pattern is distinctive. More details on solar recordings, and the ongoing Solar Recording Project, are in our feature UV light in nature and in the files section of the UVB_Meter_Owners internet mailing group.

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